Project description:Acute myeloid leukemia (AML) is characterized by a block in myeloid differentiation the stage of which is dependent on the nature of the transforming oncogene and the developmental stage of the oncogenic hit. This is also true for the t(8;21) translocation which gives rise to the RUNX1/ETO fusion protein and initiates the most common form of human AML. To understand the molecular principles governing this differential action, we used the differentiation of mouse embryonic stem cells expressing an inducible RUNX1/ETO protein into blood cells as a traceable model combined with genome-wide analyses of transcription factor binding and gene expression. We found that RUNX1/ETO interferes with both the activating and repressive function of its normal counterpart, RUNX1, at early and late stages of blood cell development. However, the response of the transcriptional network to RUNX1/ETO expression is stage-specific, highlighting the molecular mechanisms determining specific target cell expansion after an oncogenic hit. High throughput sequencing data have been used to study RUNX1/ETO role in hematopoietic system
Project description:Most B cell lymphomas arise in the germinal center (GC), where humoral immune responses evolve from potentially oncogenic cycles of mutation, proliferation, and clonal selection. Although lymphoma gene expression diverges significantly from GC-B cells, underlying mechanisms that alter the activities of corresponding regulatory elements (REs) remain elusive. Here we define the complete pathogenic circuitry of human follicular lymphoma (FL), which activates or decommissions transcriptional circuits from normal GC-B cells and commandeers enhancers from other lineages. Moreover, independent sets of transcription factors, whose expression is deregulated in FL, target commandeered versus decommissioned REs. Our approach reveals two distinct subtypes of low-grade FL, whose pathogenic circuitries resemble GC-B or activated B cells. Remarkably, FL-altered enhancers also are enriched for sequence variants, including somatic mutations, which disrupt transcription factor binding and expression of circuit-linked genes. Thus, the pathogenic regulatory circuitry of FL reveals distinct genetic and epigenetic etiologies for GC-B transformation. Molecular profiling of follicular lymphoma, resting peripheral blood and tonsillar B cells using Formaldehyde-Assisted Isolation of Regulatory Elements (FAIRE) and chromatin immunoprecipitation (H3ac and H3K27ac).
Project description:Pericentric heterochromatin silencing at mammalian centromeres is essential for mitotic fidelity and genomic stability. Defective pericentric silencing is observed in senescent cells, aging tissues, and mammalian tumors, but the underlying mechanisms and functional consequences of these defects are unclear. Here, we uncover a pivotal role of the human SIRT6 enzyme in pericentric transcriptional silencing, and this function protects against mitotic defects, genomic instability, and cellular senescence. At pericentric heterochromatin, SIRT6 promotes deacetylation of a new substrate, histone H3 lysine K18 (H3K18), and inactivation of SIRT6 in cells leads to H3K18 hyperacetylation and aberrant accumulation of pericentric transcripts. Strikingly, RNAi-depletion of these transcripts rescues the mitotic and senescence phenotypes of SIRT6-deficient cells. Together, our findings reveal a new function for SIRT6 and H3K18Ac regulation at heterochromatin, and demonstrate the pathogenic role of de-regulated pericentric transcription in aging- and cancer- related cellular dysfunction. H3K18ac, H3K9ac, H3K9me3, H3K56ac and Input ChIP-seq for U2OS cell
Project description:Mammalian development is regulated by the interplay of tissue-specific and ubiquitously expressed transcription factors, such as Sp1. Sp1 knock-out mice die in utero with multiple phenotypic aberrations, but the underlying molecular mechanism of this differentiation failure has been elusive. Here we used conditional knock-out mice as well as the differentiation of mouse ES cells as a model to address this issue. To this end we examined differentiation potential, global gene expression patterns and Sp1 target regions in Sp1 wild-type and deficient cells representing different stages of hematopoiesis. Sp1-/- cells progress through most embryonic stages of blood cell development but cannot complete terminal differentiation. For most Sp1 target and non-target genes, gene expression is unaffected by Sp1 inactivation. However, Cdx and multiple Hox genes are stage-specific targets of Sp1 and are down-regulated at an early stage. As a consequence, expression of genes involved in hematopoietic specification are progressively deregulated, highlighting the regulatory hierarchy of hematopoietic specification. Our work demonstrates that the early absence of active Sp1 sets a cascade in motion that culminates in a failure of terminal hematopoietic differentiation and emphasizes the role of ubiquitously expressed transcription factors for tissue-specific gene regulation. Two ChIP-Seq data from Sp1 transcription factor obtained from FLK+ and progenitor cells
Project description:Eukaryotic RNA polymerase II (Pol II) has evolved an array of heptad repeats with the consensus sequence Tyr1-Ser2-Pro3-Thr4-Ser5-Pro6-Ser7 at the carboxy-terminal domain (CTD) of the large subunit (Rpb1). Differential phosphorylation of Ser2, Ser5, and Ser7 in the 5’ and 3’ regions of genes coordinates the binding of transcription and RNA processing factors to the initiating and elongating polymerase complexes. Here, we report phosphorylation of Thr4 by Polo-like-kinase-3 in mammalian cells. ChIPseq analyses indicate an increase of Thr4-P levels in the 3’ region of genes occurring subsequently to an increase of Ser2-P levels. A Thr4/Ala mutant of Pol II displays a lethal phenotype. This mutant reveals a global defect in RNA elongation, while initiation is largely unaffected. Since Thr4 replacement mutants are viable in yeast we conclude that this amino acid has evolved an essential function(s) in the CTD of Pol II for gene transcription in mammalian cells. In this study, we investigated the function and ChIPseq genome-wide profiling of Thr4P residue (using the 6D7 antibody) of the Pol II CTD in Raji human B cells in comparison with either total Pol II profiling (N20 antibody, santa-cruz sc-899x), Ser5P CTD (3E8) or Ser2P (3E10) profiling in WT Raji cells. In another set of experiments, we also analysed total Pol II profiling (using an HA tag at the N-terminus of RPB1 and HA antibody Abcam ab9110) when endogenous enzyme is shut down by alpha-amanitin and replaced by either a recominant Pol II with 48 consensus repeats of the CTD (con48) or a mutated version where Thr4 residues were replaced by Ala (Thr4-Ala).In total 6 experimental sets (Pol IIt, Ser5P, Ser2P, Thr4P, con48, Thr4-Ala) were generated for our analysis and for each a biological replicate was performed. Biological replicates were merged when the data showed comparable signal noise ratio. Otherwise a unique replicate, showing the best noise ratio, was chosen for further analysis although the second replicate (for Ser2P and Thr4-Ala experiments). An input control (genomic DNA extracted after reverse crosslinking of the nuclear chip extracts) was performred and used for substraction to the ChIP experiments. One specific input material was used for wt cells, one for con48 and one for Thr4-Ala. Our data were processed to generate final wig files using our in house analysis pipeline essentially as described in Koch et al, (2011) NSMB 18 (8) p956.In brief, after alignment, sequence tags are: (i) artefact removed, (ii) elongated to an in silico optimized actual size of the initial fragments , (iii) input substracted, (iv) merged if applicable, (v) scaled for all experiments to correct for variation of tag number in between experiments. Several of the raw data files were no longer available.
Project description:We determined genome-wide nucleosome occupancy in mouse embryonic stem cells and their neural progenitor and embryonic fibroblast counterparts to assess features associated with nucleosome positioning during lineage commitment. Cell type and protein specific binding preferences of transcription factors to sites with either low (e.g. Myc, Klf4, Zfx) or high (e.g. Nanog, Oct4 and Sox2) nucleosome occupancy as well as complex patterns for CTCF were identified. Nucleosome depleted regions around transcription start and termination sites were broad and more pronounced for active genes, with distinct patterns for promoters classified according to their CpG-content or histone methylation marks. Throughout the genome nucleosome occupancy was dependent on the presence of certain histone methylation or acetylation modifications. In addition, the average nucleosome-repeat length increased during differentiation by 5-7 base pairs, with local variations for specific genomic regions. Our results reveal regulatory mechanisms of cell differentiation acting through nucleosome repositioning. For chromatin immunoprecipitation, for each sample, 1 x 106 cells were cross-linked with 1% PFA and cell nuclei were prepared using a swelling buffer (25 mM Hepes pH 7.8, 1 mM MgCl2, 10 mM KCl, 0.1% NP-40, 1 mM DTT). Chromatin was sheared to mononucleosomal fragments. After IgG preclearance the sheared chromatin was incubated with 4 µg of either a H3K9ac (Abcam, ab4441), a H3K27ac (Abcam, ab4729), or a H3K9me3 (Abcam ab8898) antibody over night. After washes with sonication (10 mM Tris-HCl, pH 8.0, 200 mM NaCl, 1 mM EDTA, 0.5% N-lauroylsarcosine, 0.1% Na-deoxycholate), high-salt- (50 mM Hepes pH 7.9, 500 mM NaCl, 1mM EDTA, 1% Triton X-100, 0.1% Na-deoxycholate, 0.1% SDS), lithium- (20 mM Tris-HCl pH 8.0, 1mM EDTA, 250 mM LiCl, 0.5% NP-40, 0.5% Na-deoxycholate) and 10 mM Tris-HCl, chromatin was eluted from the protein G magnetic beads and the crosslink was reversed over night. After RNase A and proteinase K digestion, the DNA was purified and subsequently cloned into a multiplexed Illumina library according to standard protocols. Sequenced 50 bp reads were mapped with bowtie and subsequently clustered with MACS 55 implemented in the Genomatix software suite (Genomatix, Munich, Germany) using a p-value of 10-5.
Project description:Rag1 and Rag2 gene expression in CD4+CD8+ double positive (DP) thymocytes depends on the activity of a distant anti-silencer element (ASE) that counteracts the activity of an intergenic silencer. However, the mechanistic basis for ASE activity is unknown. Here we show that the ASE physically interacts with the distant Rag1 and Rag2 gene promoters in DP thymocytes, bringing the two promoters together to form an active chromatin hub. Moreover, we show that the ASE functions as a classical enhancer that can potently activate these promoters in the absence of the silencer or other locus elements. In thymocytes lacking the chromatin organizer SATB1, we identified a partial defect in Tcra gene rearrangement that was associated with reduced expression of Rag1 and Rag2 at the DP stage. SATB1 binds to the ASE and Rag promoters, facilitating inclusion of Rag2 in the chromatin hub and the loading of RNA polymerase II to both the Rag1 and Rag2 promoters. Our results provide a novel framework for understanding ASE function and demonstrate a novel role for SATB1 as a regulator of Rag locus organization and gene expression in DP thymocytes. Sequencing of Satb1-ChIP and input control from 6 wk old thymus
Project description:Sequencing DNA fragments associated with proteins following in vivo cross-linking with formaldehyde (known as ChIP-seq) has been used extensively to describe the distribution of proteins across genomes. It is not widely appreciated that this method merely estimates a protein’s distribution and cannot reveal changes in occupancy between samples. To do this, we tagged with the same epitope orthologous proteins in Saccharomyces cerevisiae and Candida glabrata, whose sequences have diverged to a degree that most DNA fragments longer than 50 bp are unique to just one species. By mixing defined numbers of C.glabrata cells (the calibration genome) with S.cerevisiae samples (the experimental genomes) prior to chromatin fragmentation and immunoprecipitation, it is possible to derive a quantitative measure of occupancy (the occupancy ratio – OR) that enables a comparison of occupancies not only within but also between genomes. We demonstrate for the first time that this “internal standard” calibration method satisfies the sine qua non for quantifying ChIP-seq profiles, namely linearity over a wide range. Crucially, by employing functional tagged proteins, our calibration process describes a method that distinguishes genuine association within ChIP-seq profiles from background noise. Our method is applicable to any protein, not merely highly conserved ones, and obviates the need for the time consuming, expensive, and technically demanding quantification of ChIP using PCR, which can only be performed on individual loci. As we demonstrate for the first time in this paper, calibrated ChIP-seq represents a major step towards documenting the quantitative distributions of proteins along chromosomes in different cell states, which we term biological chromodynamics. Develop a method for quantitative ChIP-seq
Project description:Cohesin stably holds together the sister chromatids from S phase until mitosis. To do so, cohesin must be protected against its cellular antagonist Wapl. Eco1 acetylates cohesin’s Smc3 subunit, which locks together the sister DNAs. We used yeast genetics to dissect how Wapl drives cohesin from chromatin and identified mutants of cohesin that are impaired in ATPase activity but remarkably confer robust cohesion that bypasses the need for the cohesin protectors Eco1 in yeast and Sororin in human cells. We uncover an unexpected functional asymmetry within the heart of cohesin’s highly conserved ABC-like ATPase machinery and show that an activity associated with one of cohesin’s two ATPase sites drives DNA release from cohesin rings. This key mechanism is conserved from yeast to humans. We propose that Eco1 locks cohesin rings around the sister chromatids by counteracting an asymmetric cohesin-associated ATPase activity. Effect of mutations in Smc1 and Smc3 on cohesin loading onto chromosomes