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Xist exploits three-dimensional chromosome architecture to spread across the X-chromosome

ABSTRACT: Many large noncoding RNAs (lncRNAs) regulate chromatin, but the mechanisms by which they localize to genomic targets remain unexplored. Here we investigate the localization mechanisms of Xist during X-chromosome inactivation (XCI), a paradigm of lncRNA-mediated chromatin regulation. During the maintenance of XCI, Xist binds broadly across the X-chromosome. During initiation of XCI, Xist initially transfers to distal regions across the X-chromosome that are not defined by specific sequences. Instead, Xist identifies these regions by exploiting the three-dimensional conformation of the X-chromosome. Xist initially accumulates on the periphery of actively transcribed regions and requires its silencing domain to spread across active regions. This suggests a model where Xist coats the entire X-chromosome by searching in three dimensions, modifying chromosome structure, and spreading to newly accessible locations. We examined the genomic localization of the Xist lncRNA using RNA Antisense Purification (RAP) in multiple cell contexts: 1) differentiated female cells (MLFs); 2) a time-course of Xist localization in male embryonic stem (ES) cells where the endogenous Xist promoter is replaced by a tet-inducible one (pSM33); 3) a time-course of Xist localization in differentiating female ES cells (F1 2-1); and 4) wild-type (delXF6) and A-repeat deletion (delSXC9) Xist transgenes incorporated into the Hprt locus under the control of a tet-inducible promoter.

ORGANISM(S): Mus musculus

SUBMITTER: Jesse Engreitz

PROVIDER: E-GEOD-46918 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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High-resolution chromosomal maps of Xist RNA reveal a two-step spreading mechanism during X-inactivation

Project description:The Xist long noncoding RNA (lncRNA) is essential for X-chromosome inactivation (XCI), the process by which mammals compensate for unequal numbers of sex chromosomes. During XCI, Xist coats the future inactive X (Xi) and recruits Polycomb Repressive Complex 2 (PRC2) to the X-inactivation center (Xic). Currently unclear is how Xist spreads silencing on a 150 Mb scale. Here we generate high-resolution maps of Xist binding across a developmental time course using CHART-seq. In female cells undergoing XCI de novo, Xist follows a two-step mechanism in which it initially targets gene-rich islands before spreading to intervening gene-poor domains. Xist is depleted from genes that escape XCI but frequently concentrates near escapee boundaries. Xist binding was linearly proportional to PRC2 density and H3 lysine 27 trimethylation (H3K27me3), suggesting co-migration of Xist and PRC2. Interestingly, when the Xi is acutely stripped of Xist in post-XCI cells, Xist recovers quickly within both gene-rich and -poor domains on a time scale of hours instead of days, suggesting a previously primed Xi chromatin state. We conclude that Xist spreading takes on distinct stage-specific forms: During initial establishment, Xist follows a two-step mechanism, but during maintenance, Xist spreads rapidly to both gene-rich and -poor regions. Capture hybridization analysis of RNA targets (CHART) and input samples of (differentiating) mouse embryonic stem (ES) cells and immortalized mouse embryonic fibroblasts (MEF) using paired-end 75 nt reads on Illumina HiSeq2500, with 2 replicates per sample (# of samples). RNA-seq of the same cell lines with 50 nt reads on Illumina HiSeq2000, with 2 replicates per sample (2 samples, 4 datasets total). CHIP-seq: Data from GSE36905 was aligned and processed as CHART-seq samples. Resulting coverage tracks (EZH2/K27me3) are linked directly to GSE48649 (bedGraphs linked below).

2013-11-04 | E-GEOD-48649 | biostudies-arrayexpress

RNAseq in Dppa2 knockout or wildtype TX1072 ESC during and after Xist over-expression

Project description:To understand the role of DPPA2 in epigenetic memory during X-Chromosome reactivation (XCR) we employed inducible Xist hybrid female embryonic stem cell line (TX1072, hybrid Bl6/Cast). Wild type or Dppa2 knockout TX1072 cells were cultured, in three or two independent biological replicates, respectively, in presence of DOX (1ug/ml) for 6 days to induce Xist overexpression and X-Chomosome inactivation (XCI) on the Bl6 allele. DOX was then washed out to silence Xist and XCR was followed in a time-series at 1, 3 or 7 days after DOX removal. Cell pellets were harvested at the following timepoints: -DOX, +DOX, 1d D-wo, 3d D-wo and 7d D-wo. RNA was extracted and 250 ng used for PolyA mRNA library preparation and Next generation sequencing.

2021-11-23 | E-MTAB-11183 | biostudies-arrayexpress

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Project description:We developed a general method based on RNA Antisense Purification (RAP) to identify the intermolecular RNA-RNA interactions of a target RNA (RAP-RNA). RAP-RNA identifies endogenous RNA-RNA complexes through in vivo crosslinking, RNA capture with antisense oligonucleotides, and high-throughput RNA sequencing. This approach provides a systematic view of other RNAs that interact with a target RNA, and furthermore can distinguish between direct and indirect RNA-RNA interactions through the use of crosslinking reagents with different reactivities with proteins and nucleic acids. We applied this method to numerous small and large noncoding RNAs, including U1 snRNA, Malat1 lncRNA, Xist lncRNA, U3 snoRNA, U17/Snora73a snoRNA and U12 snRNA. We examined the RNA and chromatin interactions of ncRNAs in mouse embryonic stem cells. We developed and applied three related protocols: RAP-RNA[AMT], RAP-RNA[FA], and RAP-RNA[FA-DSG]. In the RAP-RNA[AMT] protocol, we fixed direct RNA-RNA hybrids in mouse embryonic stem (ES) cells with 4'-aminomethyltrioxalen (AMT), a psoralen-derivative crosslinker; AMT generates inter-strand crosslinks between uridine bases in RNA but does not react with proteins. In the RAP-RNA[FA] protocol, we used a different crosslinking strategy to capture both direct and indirect RNA-RNA interactions: we fixed ES cells using formaldehyde (FA), which crosslinks protein-RNA and protein-protein interactions and thus can capture both indirect interactions as well as direct interactions that are caged or flanked by proteins. In the RAP-RNA[FA-DSG] protocol, we fixed with both FA and disuccinimidyl glutarate (DSG), a strong protein-protein crosslinker, to more efficiently capture RNAs linked indirectly through multiple protein intermediates.

2014-09-01 | E-GEOD-55914 | biostudies-arrayexpress

RNA-seq of mouse ES cells depleted of MOF, MSL1, MSL2 or KANSL3

Project description:We have studied the regulatory potential of MYST1-(MOF)-containing MSL and NSL complexes in mouse embryonic stem cells (ESCs) and neuronal progenitors. We find that both complexes influence transcription by binding to promoters as well as TSS-distal enhancer regions. In contrast to flies, the MSL complex is not enriched on the X chromosome yet it is crucial for mammalian X chromosome regulation as it specifically regulates Tsix ncRNA, the major repressor of Xist lncRNA. MSL depletion leads to severely decreased Tsix expression, reduced REX1 recruitment, and consequently accumulation of Xist RNA in ESCs. The NSL complex provides additional, Tsix-independent repression of Xist by maintaining pluripotency. MSL and NSL complexes therefore act synergistically by using distinct pathways to ensure a fail-safe mechanism for the repression of X inactivation in ESCs. We have performed ChIP-seq of KANSL3, MCRS1, MOF, MSL1 and MSL2 in mouse ESCs, and KANSL3, MOF and MSL2 in NPCs, in duplicate and normalised against their inputs. We have also performed RNA-seq following knockdown of Kansl3, Mof, Msl1 and Msl2 mouse embryonic stem cells in triplicate. NB: Kansl3 and Mof knockdown-RNAseq are analyzed against their own scrambled controls, and Msl1 and Msl2 against another scrambled control triplicate.

2014-06-03 | E-GEOD-57698 | biostudies-arrayexpress

SPEN is a molecular integrator that bridges Xist with transcriptional and epigenetic control of X-chromosome inactivation

Project description:Xist represents a paradigm for long non-coding RNA function in epigenetic regulation, although how it mediates X-chromosome inactivation (XCI) remains largely unexplained. Multiple Xist-RNA binding proteins have recently been identified, including SPEN/SHARP, whose knockdown has been associated with deficient XCI at multiple loci. Here we demonstrate that SPEN is a key orchestrator of XCI in vivo and unravel its mechanism of action. We show that SPEN is essential for initiating gene silencing on the X chromosome in preimplantation mouse embryos and embryonic stem cells. On the other hand, SPEN is dispensable for maintenance of XCI in neural progenitor cells, although it significantly dampens expression of genes that escape from XCI. During initiation of XCI, we show by live-cell imaging and CUT&RUN approaches that SPEN is immediately recruited to the X chromosome upon Xist up-regulation, where it is targeted to enhancers and promoters of actively transcribed genes. SPEN rapidly disengages from chromatin once silencing is accomplished, implying a need for active transcription to tether it to chromatin. We define SPEN’s SPOC (SPEN paralog and ortholog C-terminal) domain as a major effector of SPEN’s gene silencing function, and show that artificial tethering of SPOC to Xist RNA is sufficient to mediate X-linked gene silencing. We identify SPOC’s protein partners which include NCOR/SMRT, the m6A RNA methylation machinery, the NuRD complex, RNA polymerase II and factors involved in regulation of transcription initiation and elongation. We propose that SPEN acts as a molecular integrator for initiation of XCI, bridging Xist RNA with the transcription machinery as well as nucleosome remodelers and histone deacetylases, at active enhancers and promoters.

2021-04-19 | PXD015699 | Pride

Xist recruits the X chromosome to the nuclear lamina to enable chromosome-wide silencing

Project description:Xist orchestrates X chromosome inactivation, a process that entails chromosome-wide silencing and remodeling of the 3-dimensional structure of the X chromosome. Yet, it remains unclear whether these changes in nuclear structure are mediated by Xist and whether they are required for silencing. Here we show that Xist directly interacts with the Lamin B Receptor (LBR), an integral component of the nuclear lamina, and that this interaction is required for Xist-mediated silencing. We show that this interaction recruits the inactive X to the nuclear lamina and by doing so enables Xist to spread to actively transcribed genes across the X. Our results demonstrate that lamina recruitment changes the accessibility of DNA thereby enabling Xist, and its silencing proteins, to spread across the X to silence transcription. We examined the genomic localization of the Xist lncRNA using RNA Antisense Purification (RAP) in male mouse ES cells where the endogenous Xist promoter is replaced by a tet-inducible one (pSM33) containing 1) wild-type Xist (WT), 2) A-repeat deletion Xist (dA), 3) LBR binding site deletion Xist (dLBS), 4) dLBS-Xist rescued with LMNB1 (LMNB1Res), 5) LBR CRISPRi knock down (LBRKD), or 6) SHARP CRISPRi knock down (SHARPKD).

2016-07-24 | E-GEOD-80510 | biostudies-arrayexpress

The efficiency of Xist-mediated silencing of X-linked and autosomal genes is determined by the genomic environment

Project description:Xist is indispensable for X chromosome inactivation (XCI) in female mammalian cells. However, how Xist RNA directs chromosome-wide transcriptional inactivation of the X chromosome is largely unknown. Here, to study chromosome inactivation by Xist, we generated a system where ectopic Xist expression can be induced from several genomic contexts in aneuploid mouse ES cells. We found that ectopic Xist expression from any location on the X chromosome faithfully recapitulated endogenous XCI, showing the potency of Xist to initiate XCI. Genes that escape XCI remain consistently transcriptionally active upon ectopic XCI, regardless of their position relative to Xist transgenes, and the enrichment of CTCF at their promoters is implicated in directing XCI escape. Xist expression from autosomes facilitates their transcriptional silencing to different degrees, and gene density in proximity of the Xist transcription locus plays a central role in determining the efficiency of gene inactivation. We also show that the enrichment of LINE elements together with a specific chromatin environment facilitates Xist-mediated silencing of both X-linked and autosomal genes. These findings provide new insights into the epigenetic mechanisms that mediate XCI and identify genomic features that promote Xist-mediated chromosome-wide gene inactivation

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Derivation of pre-X inactivation human embryonic stem cells under physiological oxygen concentrations

Project description:The presence of two active X chromosomes (XaXa) is a hallmark of the ground state of pluripotency specific to murine embryonic stem cells (ESCs). Human ESCs invariably exhibit signs of X chromosome inactivation (XCI) and are considered developmentally more advanced than their murine counterparts. We describe the establishment of the first XaXa hESCs derived under physiological oxygen concentrations. Using these cell lines we demonstrate that (1) differentiation of hESCs induces random XCI in a manner similar to murine ESCs, (2) chronic exposure to atmospheric oxygen is sufficient to induce irreversible XCI with minor changes of the transcriptome, (3) the Xa exhibits heavy methylation of the XIST promoter region, and (4) XCI is associated with demethylation and transcriptional activation of XIST along with H3K27-me3 deposition across the Xi. These findings indicate that the human blastocyst contains pre-X-inactivation cells and that this state is preserved in vitro through culture under physiological oxygen. Examination of 2 different histone modifications (H3K4me3 and H3K27me3) in 3 ES cell lines in 5% and 20% oxygen.

2010-05-28 | E-GEOD-21141 | biostudies-arrayexpress

The role of early chromatin changes in X chromosome inactivation

Project description:During development, transcriptional and chromatin modification changes co-occur but the order and causality of events often remain unclear. We explore the interrelationship of these processes using the paradigm of X-chromosome inactivation (XCI). We initiate XCI in female, mouse embryonic stem cells by inducing Xist expression and monitor changes in transcription and chromatin by allele-specific TT-seq and ChIP-seq respectively. An unprecedented temporal resolution enabled identification of the earliest chromatin alterations during XCI. We demonstrate that HDAC3 interacts with both NCOR1 and NCOR2 and is pre-bound on the X chromosome where it deacetylates histones to promote efficient gene silencing. We also reveal the choreography of polycomb accumulation following Xist RNA coating, with PRC1-associated H2AK119Ub preceding PRC2-associated H3K27me3. Furthermore, polycomb-associated marks accumulate initially at large, intergenic domains and then spreads into genes but only in the context of gene silencing. Our results provide the hierarchy of chromatin events during XCI and demonstrate that some chromatin changes play key roles in mediating transcriptional silencing.

2019-01-17 | PXD011344 | Pride

ChIP-sequencing (ChIP-seq) experiments on female ESCs expressing V5-tagged REX1 and control wild-type Embryonic stem cells (ESCs)

Project description:Evolution of the mammalian sex chromosomes has resulted in a heterologous X and Y pair, where the Y chromosome has lost most of its genes. Hence, there is a need for X-linked gene dosage compensation between XY males and XX females. In placental mammals, this is achieved by random inactivation of one X chromosome (XCI) in all female somatic cells. Up-regulation of Xist transcription on the future inactive X chromosome (Xi) acts against Tsix antisense transcription, and spreading of Xist RNA in cis triggers epigenetic changes leading to XCI. Previously, we have shown that the X-encoded E3 ubiquitin ligase RNF12 is up-regulated in differentiating mouse embryonic stem cells (ESCs) and activates Xist transcription and XCI. Here, we have identified the pluripotency factor REX1 as a key target of RNF12 in the XCI mechanism. RNF12 causes ubiquitination and proteasomal degradation of REX1, and Rnf12 knockout mouse ESCs show an increased level of REX1. Using ChIP-seq, REX1 binding sites were detected in Xist and Tsix regulatory regions. Over-expression of REX1 in female ESCs was found to inhibit Xist transcription and XCI, whereas male Rex1+/- ESCs showed ectopic XCI. From this, we propose that RNF12 causes REX1 breakdown through dose-dependent catalysis, thereby representing an important pathway to initiate XCI. Rex1 and Xist are present only in placental mammals, which points to co-evolution of these two genes and XCI. 2 (one control one pulldown) samples

2012-06-12 | E-GEOD-36417 | biostudies-arrayexpress

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