This SuperSeries is composed of the SubSeries listed below.
Reprogramming factor expression initiates widespread targeted chromatin remodeling.
Specimen part
View SamplesDespite rapid progress in characterizing transcription factor-driven reprogramming of somatic cells to an induced pluripotent stem (iPS) cell state, many mechanistic questions still remain. To gain insight into the earliest events in the reprogramming process, we systematically analyzed the transcriptional and epigenetic changes that occur during early factor induction after discrete numbers of divisions. We observed rapid, genome-wide changes in the euchromatic histone modification, H3K4me2, at more than a thousand loci including large subsets of pluripotency or developmentally related gene promoters and enhancers. In contrast, patterns of the repressive H3K27me3 modification remained largely unchanged except for focused depletion specifically at positions where H3K4 methylation is gained. These chromatin regulatory events precede transcriptional changes within the corresponding loci. Our data provide evidence for an early, organized, and population-wide epigenetic response to ectopic reprogramming factors that clarify the temporal order through which somatic identity is reset during reprogramming.
Reprogramming factor expression initiates widespread targeted chromatin remodeling.
Specimen part
View SamplesConcerted efforts over past decades have established a thorough understanding of the canonical somatic DNA methylation landscape as well as its systematic misregulation across most human cancers. However, the underlying mechanism that directs this genome-scale transformation remains elusive, with no clear model for its acquisition or understanding of its potential developmental utility. Here we present base pair resolution analysis of global remethylation from the hypomethylated state of the preimplantation embryo into the early epiblast and extraembryonic ectoderm. We show that these two states acquire highly divergent genomic distributions: while the proximal epiblast establishes a canonical CpG-density dependent pattern found in somatic cells, the extraembryonic epigenome becomes substantially more mosaic. Moreover, this alternate pattern includes specific de novo methylation of hundreds of CpG island promoter containing genes that function in early embryonic development and are orthologously methylated across an extensive cohort of human cancers. From these data, we propose a model where the evolutionary innovation of extraembryonic tissues in eutherian mammals required cooption of DNA methylation-based suppression as an alternate pathway to the embryonically utilized Polycomb group proteins, which otherwise coordinate germ layer formation in response to extraembryonic cues at the onset of gastrulation. Moreover, we establish that this decision is made deterministically downstream of the promiscuously utilized, and frequently oncogenic, FGF signaling pathway and utilizes a novel combination of epigenetic cofactors. Recruitment of this silencing mechanism to developmental genes during cancer therefore reflects the misappropriation of an innate regulatory pathway that may be spontaneously sampled as an alternate epigenetic landscape within somatic cells. Overall design: Comparison of gene expression patterns in Extraembryonic Ectoderm and cancer
Epigenetic restriction of extraembryonic lineages mirrors the somatic transition to cancer.
Treatment, Subject
View SamplesDNA methylation is a mechanism of epigenetic regulation that is common to all vertebrates. Functional studies support its relevance for tissue homeostasis, but the global dynamics of DNA methylation during in vivo differentiation have not been worked out in detail. Here we report high-resolution DNA methylation maps of adult stem cell differentiation in mouse, focusing on 19 purified cell populations of the blood and skin lineages. Except for global demethylation in erythrocytes, observed DNA methylation changes were locus-specific and relatively modest in size. They frequently overlapped with lineage-associated transcription factors and their binding sites, suggesting that DNA methylation may protect cells from aberrant transcription factor activation. DNA methylation and gene expression provided highly complementary information, and combining the two enabled us to infer the blood lineage hierarchy directly from genomic data. In summary, our dataset and analysis demonstrate that in vivo differentiation of adult stem cells is associated with small but informative changes in the distribution of DNA methylation across the mouse genome.
DNA methylation dynamics during in vivo differentiation of blood and skin stem cells.
Specimen part
View SamplesThe developmental potential of human pluripotent stem cells suggests that they can produce disease-relevant cell types for biomedical research. However, substantial variation has been reported among pluripotent cell lines, which could affect their utility and clinical safety. Such cell-line specific differences must be better understood before one can confidently use embryonic stem (ES) or induced pluripotent stem (iPS) cells in translational research. Towards this goal we have established genome-wide reference maps of DNA methylation and gene expression for 20 previously derived human ES lines and 12 human iPS cell lines, and we have measured the in vitro differentiation propensity of these cell lines. This resource enabled us to assess the epigenetic and transcriptional similarity of ES and iPS cells and to predict the differentiation efficiency of individual cell lines. The combination of assays yields a scorecard for quick and comprehensive characterization of pluripotent cell lines.
Reference Maps of human ES and iPS cell variation enable high-throughput characterization of pluripotent cell lines.
Sex, Cell line
View SamplesRegulation of RNA levels is critical for the response to external stimuli and determined through the interplay between RNA production, processing and degradation. Despite the centrality of these processes, most global studies of RNA regulation do not distinguish their separate contributions and relatively little is known about how they are temporally integrated. Here, we combine metabolic labeling of RNA with advanced RNA quantification assays and computational modeling to estimate RNA transcription and degradation during the response of immune dendritic cells (DCs) to pathogens, a critical and tightly regulated step in innate immunity. We find that transcription regulation plays a major role in shaping most temporal changes in RNA levels, but that changes in degradation rate are important for shaping sharp ‘peaked’ responses. We find that transcription changes precede corresponding RNA changes by a small lag (15-30 min), which is shorter for induced than for repressed genes. Massively parallel sequencing of the entire RNA population – including non-polyadenylated transcripts – allows us to estimate RNA processing, and identify specific groups of transcripts, mostly cytokines and transcription factors, undergoing enhanced mRNA maturation. This suggests an additional role for splicing in regulating mRNA maturation. Our method provides a new quantitative approach to study key steps in the integrative process of RNA regulation. Overall design: Sequencing of 4sU-labeled RNA taken from a 7 samples time-series (one sample every 1 hour) during the response of DCs to LPS stimulation. 4-thiouridine was added 45 minutes prior to sample collection. Data presented here for six timepoints: 0, 1, 3-6 hrs. 2hr timepoint not included.
Metabolic labeling of RNA uncovers principles of RNA production and degradation dynamics in mammalian cells.
No sample metadata fields
View SamplesExpression profiles for Gfap-positive astrocytes obtained by in vitro differentiation of 129SvJae x C57BL/6 murine embryonic stem (ES) cells. Generated to examine the relationship between expression levels and DNA methylation patterns.
Genome-scale DNA methylation maps of pluripotent and differentiated cells.
No sample metadata fields
View SamplesRNA-Seq is an effective method to study the transcriptome, but can be difficult to apply to scarce or degraded RNA from fixed clinical samples, rare cell populations, or cadavers. Recent studies have proposed several methods for RNA-Seq of low quality and/or low quantity samples, but their relative merits have not been systematically analyzed. Here, we compare five such methods using a comprehensive set of metrics, relevant to applications such as transcriptome annotation, transcript discovery, and gene expression. Using a single human RNA sample, we constructed and deeply sequenced 10 libraries with these methods and two control libraries. We find that the RNase H method performed best for low quality RNA, and can even effectively replace oligo (dT) based methods for standard RNA-Seq. SMART and NuGEN had distinct strengths for low quantity RNA. Our analysis allows biologists to select the most suitable methods and provides a benchmark for future method development. Overall design: Examination of 9 different RNA-Seq libraries starting from total RNA from 5 distinct methods; also 3 control RNA-Seq libraries
Comparative analysis of RNA sequencing methods for degraded or low-input samples.
Specimen part, Cell line, Subject
View SamplesCancer evolution is fueled by genetic and epigenetic diversity, and intra-tumoral heterogeneity in DNA methylation has been shown to co-operate with genetic heterogeneity to empower evolutionary capacity of cancers such as chronic lymphocytic leukemia. Here, we show that epigenetic diversification leads to decreased coordination across layers of epigenetic information, likely reflecting an admixture of cells with diverging epigenetic identities. This manifests in incomplete gene silencing by the Polycomb complex, unexpected co-occurrence of typically mutually exclusive activating and repressing histone modifications, and greater cell-to-cell transcriptional heterogeneity. Overall design: Given the importance of histone modifications to lineage plasticity in cancer15-17, intra-leukemic epigenetic heterogeneity may extend to histone modifications, likely promoting lineage plasticity by enabling permissive chromatin states. To address this question, we complemented DNAme analysis with a chromatin immunoprecipitation sequencing (ChIP-seq) compendium of histone post-translational modifications (H3K4me3, H3K27ac, H3K4me1, H3K27me3, H3K9me3 and H3K36me3) and transcriptome sequencing (RNA-seq) in a cohort of primary CLL and healthy B lymphocytes samples (CLL IGHV unmutated, n = 12; CLL IGHV mutated, n = 10; peripheral blood NBCs [CD23+CD19+CD27-IgD+], peripheral blood memory B cells [GCBs; CD23+CD19+CD27+IgD-], peripheral blood CD20+ cells.
Corrupted coordination of epigenetic modifications leads to diverging chromatin states and transcriptional heterogeneity in CLL.
No sample metadata fields
View SamplesWe describe Hi-C, a method that probes the three-dimensional architecture of whole genomes by coupling proximity-based ligation with massively parallel sequencing. We constructed spatial proximity maps of the human genome with Hi-C at a resolution of 1Mb. These maps confirm the presence of chromosome territories and the spatial proximity of small, gene-rich chromosomes. We identified an additional level of genome organization that is characterized by the spatial segregation of open and closed chromatin to form two genome-wide compartments. At the megabase scale, the chromatin conformation is consistent with a fractal globule, a knot-free conformation that enables maximally dense packing while preserving the ability to easily fold and unfold any genomic locus. The fractal globule is distinct from the more commonly used globular equilibrium model. Our results demonstrate the power of Hi-C to map the dynamic conformations of whole genomes.
Comprehensive mapping of long-range interactions reveals folding principles of the human genome.
Cell line
View Samples