SMAD2/3 interactome in human pluripotent stem cells
ABSTRACT: This experiment was designed to determine the interactome of SMAD2/3 in human pluripotent stem cells (hPSCs). hPSCs were cultured in standard pluripotency-promoting conditions, or induced to differentiate towards the definitive endoderm lineage for 36h. Endogenous SMAD2/3 was immunoprecipitated from nuclear extracts in these two conditions using a specific antibody. Non-immune IgG immunoprecipitations were performed as negative controls. Three biological replicates per conditions were analyzed by quantitative label-free mass spectrometry.
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:While it has been clearly established that well positioned H2A.Z-containing nucleosomes flank the nucleosome depleted region (NDR) at the transcriptional start site (TSS) of active mammalian genes, how this chromatin-based information is transmitted through the cell cycle is unknown. We show here that in trophoblast stem (TS) cells, the level of H2A.Z at promoters decreases during S phase coinciding with homotypic (H2A.Z/H2A.Z) nucleosomes flanking the TSS becoming heterotypic (H2A.Z/H2A). Surprisingly, these nucleosomes remain heterotypic at M phase. At the TSS, we identify an unstable heterotypic H2A.Z-containing nucleosome in G1 which, strikingly, is lost following DNA replication. These dynamic changes in H2A.Z at the TSS mirror a global expansion of the NDR at S and M which, unexpectedly, is unrelated to transcriptional activity. Coincident with the loss of H2A.Z at promoters, it is targeted to the centromere when mitosis begins We performed ChIP-Seq experiments (on mouse Trophoblast Stem cells arrested at G1; S and M stages of thecell cycle) using antibodies against histone variant H2A.Z and sequentional ChIP-re-ChIP-Seq experiments using H2A.Z antibody and H2A antibody in sequence. Combining those data sets with microarray gene expression expression data allowed us to see H2A.Z distribution over promoters of mouse coding genes in cell cycle dependant manner. Interestingly, Input also showed cell-cycle dependent effects, but histone H3 could be used as a cell-cycle independent normalisation factor. We also performed ChIP-seq with a CTCF pull-down to investigate its cell-cycle dependent relationship with heterochromatin.
Project description:Recent studies have revealed a myriad of non-coding transcripts in different organisms. For instances, the presence of short bidirectional transcripts is a hallmark of active promoters in mammals, while upstream non-coding transcripts can be detected at most expressed genes in conditions where the RNA degradation machinery is inhibited. Here, we used RNA-seq with very high sequencing depth to characterize strand specific transcripts from primary mouse tissues. We found that a substantial fraction of gene promoters sustain expression of long non-coding antisense transcripts. These transcripts have an average size of 6 kb, have features of mature transcripts, but remain associated with the chromatin. We named this new class of non-coding RNAs Long Upstream Antisense Transcripts (LUAT). Strikingly, the LUAT and coding gene pairs are usually co-regulated, with the associated genes often/generally coding for transcriptional regulators functioning during development and cell differentiation. Indeed, these bidirectional promoters share several characteristic of developmental gene promoters, including large CpG islands and high degree of conservation, and display symetrical GC skews. Finally, we found that bidirectional promoters have enlarged platforms of Pol II initiation, associated with an intensified rate of early transcriptional elongation. We concluded that promoters of developmental regulators are characterized by a specialized mechanism of Pol II transcription, whereby Pol II poising is directly coupled to relaxed bidirectional transcription. H3K79me2 ChIP in CD4+,CD8+ double positive thymocytes from C57BL/6 mice was studied, using Illumina sequencer
Project description:Chromatin performs numerous functions during cellular differentiation, and therefore it must be capable of adopting a multitude of different structures. How these various structures are established is poorly understood, but we propose that specific histone H2A variants will have a key role in remodelling chromatin during differentiation. Structurally, we show here that the gain of just a single acidic amino acid residue has generated a new mouse H2A.Bbd-like histone variant, H2A.Lap1, and that when incorporated into nucleosomal arrays imparts on them unique biophysical properties that are distinct from arrays containing either H2A or human H2A.Bbd. Functionally, we identify H2A.Lap1 as a novel chromatin component of active genes that are expressed during spermatogenesis, and in combination with H2A.Z create a unique chromatin landscape at the start site of transcription. During round spermatid differentiation, H2A.Lap1 dramatically loads onto the inactive X chromosome enabling a subset of its genes to be transcriptionally activated Examination of 2 different histone variants in mouse spermatids.
Project description:Activin/Nodal signalling is necessary to maintain pluripotency of human Embryonic Stem Cells (hESCs) and to induce their differentiation towards endoderm. However, the mechanisms by which Activin/Nodal signalling achieves these opposite functions remain unclear. To unravel these mechanisms, we examined the transcriptional network controlled in hESCs by Smad2 and Smad3 which represent the direct effectors of Activin/Nodal signalling. These analyses reveal that Smad2/3 participate in the control of the core transcriptional network characterising pluripotency which includes Oct-4, Nanog, FoxD3, Dppa4, Tert, Myc and UTF-1. In addition, similar experiments performed on endoderm cells confirm that a broad part of the transcriptional network directing differentiation is downstream of Smad2/3. Therefore, Activin/Nodal signalling appears to control divergent transcriptional networks in hESCs and in endoderm. Importantly, we observed an overlap between the transcriptional network downstream of Nanog and Smad2/3 in hESCs while functional studies showed that both factors cooperate to control the expression of pluripotency genes. Therefore, the effect of Activin/Nodal signalling on pluripotency and differentiation could be dictated by tissue specific Smad2/3 partners such as Nanog, explaining the mechanisms by which signalling pathways can orchestrate divergent cell fate decisions. Identification of Smad2/3 binding sites in pluripotent hESCs. 5 ChIP-Seq samples including 1 input control sample and 4 ChIP samples (two conditions x two replicates).
Project description:Several lines of recent evidence support a role for chromatin in splicing regulation. Here we show that splicing can also contribute to histone modification, which implies a bidirectional communication between epigenetics and RNA processing. Genome-wide analysis of histone methylation in human cell lines and mouse primary T cells reveals that intron-containing genes are preferentially marked with H3K36me3 relative to intronless genes. In intron-containing genes, H3K36me3 marking is proportional to transcriptional activity, whereas in intronless genes H3K36me3 is always detected at much lower levels. Furthermore, splicing inhibition impairs recruitment of H3K36 methyltransferase HYPB/Setd2 and reduces H3K36me3, whereas splicing activation has the opposite effect. Moreover, the increase of H3K36me3 correlates with the length of the first intron, consistent with the view that splicing enhances H3 methylation. We propose that splicing is mechanistically coupled to recruitment of HYPB/Setd2 to elongating RNA Polymerase II. This experiment proposes to profile genome-wide binding profiles by ChIP-seq (Illumina, 36 bp tags) of RNA polymerase II (one biological replicate), the histone modification H3K36me3 (2 replicates) and a reference control input sample (genomic DNA after reverse cross-link, one replicate) in a human H1299 lung carcinoma cell line *** Raw data not provided for Samples GSM766322-GSM766324.
Project description:Despite the impact of bile duct disorders, treatment options remain very limited. Poor access to biliary tissue and restrictions in long-term culture or significant expansion of primary cholangiocytes have posed major challenges for research in the field. These limitations have so far precluded large scale experiments such as transcriptomic and genome-wide analyses which are urgently needed to better understand biliary physiology and pathophysiology. To address this issue, we have developed a novel system for the isolation and propagation of primary cholangiocytes from the extrahepatic bile ducts. The resulting Extrahepatic Cholangiocyte Organoids (ECOs) maintain their genetic stability, transcriptomic profile and function over long term culture and are compatible with regenerative medicine applications such as biliary reconstruction. We established a novel protocol for the isolation and propagation of primary cholangiocytes from the extrahepatic biliary tree in the form of extrahepatic cholangiocyte organoids (ECOs). The aim of this experiment was to provide in depth characterisation of the transcriptome of ECOs during long term culture. We compare the transcriptome of ECOs cultured for 1 passage (P1), 10 passages (P10) and 20 passages (P20) with freshly isolated primary cholangiocytes from the common bile duct. Embryonic Stem Cells (ES) cells are used as a negative control=
Project description:One clear hallmark of mammalian promoters is the presence of CpG islands (CGIs) at more than two thirds of genes whereas TATA boxes are only present at a minority of promoters. Using genome-wide approaches, we show that GC content and CGIs are major promoter elements in mammalian cells, able to govern open chromatin conformation and support paused transcription. First, we define three classes of promoters with distinct transcriptional directionality and pausing properties which correlate with their GC content. We further analyze the direct influence of GC content on nucleosome positioning and depletion, and show that CGIs correlate with nucleosome depletion both in vivo and in vitro. We also show that transcription is not essential for nucleosome exclusion but influences both a weak +1 and a well-positioned nucleosome at CGI borders. Altogether our data support the idea that CGIs have become an essential feature of promoter structure defining novel regulatory properties in mammals. Nucleosome density and positioning were studied by high-throughput sequencing of DNA previously treated with Mnase. In parallel, chIPseq for PolII and H3K27ac were performed in mouse and human with different conditions to assess a potential effect of transcription on nucleosomes properties.
Project description:Nucleosomes are barriers to transcription in vitro, however, their effects on RNA polymerase in vivo are unknown. Here we describe a simple and general strategy to comprehensively map the positions of elongating and arrested RNA Polymerase II (RNAPII) at nucleotide resolution. Our results suggest that nucleosomes present significant, context-specific barriers to RNAPII in vivo that can be tuned by the incorporation of H2A.Z. 8 sets of two replicates each of paired-end and 3 sets of two replicates each of single-end samples were sequenced and analyzed.
Project description:Understanding the molecular mechanisms controlling early cell fate decisions in mammals is a major objective towards the development of robust methods for the differentiation of human pluripotent stem cells into clinically relevant cell types. Here, we used human embryonic stem cells (hESCs) to study specification of definitive endoderm in vitro. Using a combination of whole genome expression and ChIP-seq analyses, we established a hierarchy of transcription factors regulating endoderm specification. Importantly, pluripotency factors, namely NANOG, OCT4 and SOX2 have an essential function in this network by actively directing differentiation. Indeed, these transcription factors control the expression of EOMES, which marks the onset of endoderm specification. In turn, EOMES interacts with SMAD2/3 to initiate the transcriptional network governing endoderm formation. Together, these results provide for the first time a comprehensive molecular model connecting the transition from pluripotency to endoderm specification during mammalian development. ChIP-Seq of Eomesodermin binding in human embyonic stem cells, differentiated towards an endodermal fate for 48h in chemically-defined culture media. Includes an input DNA control. Supplementary file GSE26097_README.txt contains descriptions of the raw data files and processed data files.