Project description:X chromosome inactivation (XCI) compensates for differences in X-chromosome number between male and female mammals. XCI is orchestrated by Xist RNA, whose expression in early development leads to transcriptional silencing of one X-chromosome in the female. Knockout studies have established a requirement for Xist, with inviability of female embryos that inherit an Xist deletion from the father. Here, we report that female mice lacking Xist RNA can, surprisingly, develop and survive to term. Xist-null females are born at lower frequency and are smaller at birth, but organogenesis is mostly normal. Transcriptomic analysis indicates significant overexpression of hundreds of X-linked genes across multiple tissues. Therefore, Xist-null mice can develop to term in spite of a deficiency of dosage compensation. However, the degree of X-autosomal dosage imbalance was less than anticipated (1.14- to 1.36-fold). Thus, partial dosage compensation can be achieved without Xist, supporting the idea of inherent genome balance. Nevertheless, to date, none of the mutant mice has survived beyond weaning stage. Sudden death is associated with failure of postnatal organ maturation. Our data suggest Xist-independent mechanisms of dosage compensation and demonstrate that small deviations from X-autosomal balance can have profound effects on overall fitness. RNA-sequencing of tail-tip fibroblasts (TTFs), spleen, liver and heart tissue from Xist-null and control female mice. Sequencing performed with 50nt read length on Illumina HiSeq2000 or 2500. Data consists of 3 biological replicates for TTFs (6 datasets) and 2 biological replicates for tissues (12 datasets).
Project description:The inactive X chromosome (Xi) serves as a model to understand gene silencing on a global scale. Here, we perform identification of direct RNA interacting proteins? (iDRiP) to isolate a comprehensive protein interactome for Xist, an RNA required for Xi silencing. We discover multiple classes of interactors, including cohesins, condensins, topoisomerases, RNA helicases, chromatin remodelers and modifiers, which synergistically repress Xi transcription. Inhibiting two or three interactors destabilizes silencing. While Xist attracts some interactors, it repels architectural factors. Xist evicts cohesins from the Xi and directs an Xi-specific chromosome conformation. Upon deleting Xist, the Xi acquires the cohesin-binding and chromosomal architecture of the active X. Our study unveils many layers of Xi repression and demonstrates a central role for RNA in the topological organization of mammalian chromosomes. The RNA-seq data sets generated in this study provide a resource for examining the effects of knockdowns of various Xist-interacting proteins on gene expression. The ChIP-seq data sets provide a comprehensive set of data examining CTCF and cohesion binding the X-chromosome, and the effects of deleting Xist on CTCF and cohesion binding. The Hi-C data is an allele-specific contact map of the X-chromosome higher-order chromatin structure in mouse. RNA-seq in 3 control and 10 knockdown cell lines. ChIP-seq for CTCF, Rad21 and Smc1a in wild-type fibroblasts and Xist-deletion fibroblasts. Hi-C in wild-type and Xist-deletion fibroblasts.
Project description:Purpose: Compare the transcriptome of homogeneous XIST+ and XIST- hES cell populations. Methods: We isolated homogeneous XIST+ and XIST- cell populations. The XIST+ cells correspond to cells with a XIST cloud and one ATRX pinpoint. The XIST- cells correspond to cells with no XIST cloud and one ATRX pinpoint. Results: We took advantage of the clonal pattern of X-chromosome inactivation in H9 cells and analyzed the data in an allelic manner. By comparing the RNA-Seq data with known H9 SNPs, we identified genomic positions which were relaxed from XCI in XIST- cells compared to XIST+ cells. Conclusions: Genic as well as unannotated transcripts are massively relaxed from XCI in H9 cells when XIST expression is lost, however, this reactivation is only partial and a large region around the centromere is protected from relaxation of silencing. Total RNA (rRNA depleted) profiles of XIST+ and XIST- human embryonic stem cells
Project description:In this project, we have studied the role of Chd8 in Xist regulation and XCI initiation by means of Chd8 Knock-Downs (KD) and Knock-Out (KO).
Project description:Cloning mammals by somatic cell nuclear transfer (SCNT) is highly inefficient because of aberrant genomic reprogramming. In addition to random reprogramming errors, we hypothesized the presence of specific errors as evidenced by common anomalies among clones. We found that Xist, which normally inactivates one of the two X chromosomes in females, was ectopically expressed from the active X (Xa) chromosome in cloned mouse embryos of both sexes. Deletion of Xist on Xa normalized global gene expression and produced about a 10-fold increase in cloning efficiency. We also identified an Xist-independent mechanism that specifically downregulated a subset of X-linked genes through somatic-type repressive histone blocks. Thus, we have identified nonrandom reprogramming errors in mouse cloning, which provide promising targets for breakthroughs in SCNT cloning technology. Gene expression were measured in mouse in vitro fertilized and somatic cell cloned blastocysts. More than three biological replicates were performed in each group using defferent nuclear donor cells.
Project description: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.
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.
Project description:Purpose: Compare the transcriptome of homogeneous XIST+ and XIST- hES cell populations. Methods: We isolated homogeneous XIST+ and XIST- cell populations. The XIST+ cells correspond to cells with a XIST cloud and one ATRX pinpoint. The XIST- cells correspond to cells with no XIST cloud and one ATRX pinpoint. Results: We took advantage of the clonal pattern of X-chromosome inactivation in H9 cells and analyzed the data in an allelic manner. By comparing the RNA-Seq data with known H9 SNPs, we identified genomic positions which were relaxed from XCI in XIST- cells compared to XIST+ cells. Conclusions: Genic as well as unannotated transcripts are massively relaxed from XCI in H9 cells when XIST expression is lost, however, this reactivation is only partial and a large region around the centromere is protected from relaxation of silencing.
Project description:XIST is a long non-coding RNA (lncRNA) that mediates transcriptional silencing of X chromosome genes. Here we show that XIST is highly methylated with at least 78 N6-methyladenosine (m6A) residues, a reversible base modification whose function in lncRNAs is unknown. We show that m6A formation in XIST, as well as cellular mRNAs, is mediated by RBM15 and its paralog RBM15B, which bind the m6A-methylation complex and recruit it to specific sites in RNA. This results in methylation of adenosines in adjacent m6A consensus motifs. Furthermore, knockdown of RBM15 and RBM15B, or knockdown of the m6A methyltransferase METTL3 impairs XIST-mediated gene silencing. A systematic comparison of m6A-binding proteins shows that YTHDC1 preferentially recognizes m6A in XIST and is required for XIST function. Additionally, artificial tethering of YTHDC1 to XIST rescues XIST-mediated silencing upon loss of m6A. These data reveal a pathway of m6A formation and recognition required for XIST-mediated transcriptional repression. Three to four biological HEK293T replicates were used to perform iCLIP of endogenous YTH proteins, RBM15, and RBM15B. Crosslinking induced truncations were identified using CIMS-CITS pipeline.