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The DNA methylation field has matured from a phase of discovery and genomic characterization to one seeking deeper functional understanding of how this modification contributes to development, ageing and disease. In particular, the past decade has seen many exciting mechanistic discoveries that have substantially expanded our appreciation for how this generic, evolutionarily ancient modification can be incorporated into robust epigenetic codes. Here, we summarize the current understanding of the distinct DNA methylation landscapes that emerge over the mammalian lifespan and discuss how they interact with other regulatory layers to support diverse genomic functions. We then review the rising interest in alternative patterns found during senescence and the somatic transition to cancer. Alongside advancements in single-cell and long-read sequencing technologies, the collective insights made across these fields offer new opportunities to connect the biochemical and genetic features of DNA methylation to cell physiology, developmental potential and phenotype.
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The small intestine is well known for the function of its nutrient-absorbing enterocytes; yet equally critical for the maintenance of homeostasis is a diverse set of secretory cells, all of which are presumed to differentiate from the same intestinal stem cell. Despite major roles in intestinal function and health, understanding how the full spectrum of secretory cell types arises remains a longstanding challenge, largely due to their comparative rarity. Here, we investigate the fate specification of a rare and distinct population of small intestinal epithelial cells found in rats and humans but not mice: C FTR Hi gh E xpressers (CHEs). We use pseudotime trajectory analysis of single-cell RNA-seq data from rat intestinal jejunum to provide evidence that CHEs are specified along the secretory lineage and appear to employ a second wave of Notch-based signal transduction to distinguish these cells from other secretory cell types. We further validate the general order of transcription factors that direct these cells from unspecified progenitors within the crypt and experimentally demonstrate that Notch signaling is necessary to induce CHE fate both in vivo and in vitro . Our results suggest a model in which Notch is reactivated along the secretory lineage to specify the CHE population: a rare secretory cell type with putative functions in localized coordination of luminal pH and direct relevance to cystic fibrosis pathophysiology.
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Embryogenesis requires substantial coordination to translate genetic programs to the collective behavior of differentiating cells, but understanding how cellular decisions control tissue morphology remains conceptually and technically challenging. Here, we combine continuous Cas9-based molecular recording with a mouse embryonic stem cell-based model of the embryonic trunk to build single-cell phylogenies that describe the behavior of transient, multipotent neuro-mesodermal progenitors (NMPs) as they commit into neural and somitic cell types. We find that NMPs show subtle transcriptional signatures related to their recent differentiation and contribute to downstream lineages through a surprisingly broad distribution of individual fate outcomes. Although decision-making can be heavily influenced by environmental cues to induce morphological phenotypes, axial progenitors intrinsically mature over developmental time to favor the neural lineage. Using these data, we present an experimental and analytical framework for exploring the non-homeostatic dynamics of transient progenitor populations as they shape complex tissues during critical developmental windows.
Assuntos
Diferenciação Celular , Linhagem da Célula , Células-Tronco Embrionárias Murinas , Animais , Camundongos , Células-Tronco Embrionárias Murinas/citologia , Células-Tronco Embrionárias Murinas/metabolismo , Regulação da Expressão Gênica no Desenvolvimento , Mesoderma/citologia , Desenvolvimento Embrionário , Somitos/citologia , Somitos/metabolismoRESUMO
Transposable elements (TEs) are a major constituent of human genes, occupying approximately half of the intronic space. During pre-messenger RNA synthesis, intronic TEs are transcribed along with their host genes but rarely contribute to the final mRNA product because they are spliced out together with the intron and rapidly degraded. Paradoxically, TEs are an abundant source of RNA-processing signals through which they can create new introns1, and also functional2 or non-functional chimeric transcripts3. The rarity of these events implies the existence of a resilient splicing code that is able to suppress TE exonization without compromising host pre-mRNA processing. Here we show that SAFB proteins protect genome integrity by preventing retrotransposition of L1 elements while maintaining splicing integrity, via prevention of the exonization of previously integrated TEs. This unique dual role is possible because of L1's conserved adenosine-rich coding sequences that are bound by SAFB proteins. The suppressive activity of SAFB extends to tissue-specific, giant protein-coding cassette exons, nested genes and Tigger DNA transposons. Moreover, SAFB also suppresses LTR/ERV elements in species in which they are still active, such as mice and flies. A significant subset of splicing events suppressed by SAFB in somatic cells are activated in the testis, coinciding with low SAFB expression in postmeiotic spermatids. Reminiscent of the division of labour between innate and adaptive immune systems that fight external pathogens, our results uncover SAFB proteins as an RNA-based, pattern-guided, non-adaptive defence system against TEs in the soma, complementing the RNA-based, adaptive Piwi-interacting RNA pathway of the germline.
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Elementos de DNA Transponíveis , Íntrons , Precursores de RNA , Splicing de RNA , RNA Mensageiro , Animais , Humanos , Masculino , Camundongos , Elementos de DNA Transponíveis/genética , Drosophila melanogaster/genética , Éxons/genética , Genoma/genética , Íntrons/genética , Especificidade de Órgãos/genética , RNA de Interação com Piwi/genética , RNA de Interação com Piwi/metabolismo , Precursores de RNA/genética , Precursores de RNA/metabolismo , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Espermátides/citologia , Espermátides/metabolismo , Splicing de RNA/genética , Testículo , MeioseRESUMO
Cancer is one of the leading causes of death in the U.S., and tumorous cancers such as cervical, lung, breast, and ovarian cancers are the most common types. APOBEC3B is a nonessential cytidine deaminase found in humans and theorized to defend against viral infection. However, overexpression of APOBEC3B is linked to cancer in humans, which makes APOBEC3B a potential cancer treatment target through competitive inhibition for several tumorous cancers. Computational studies can help reveal a small molecule inhibitor using high-throughput virtual screening of millions of candidates with relatively little cost. This study aims to narrow the field of potential APOBEC3B inhibition candidates for future in vitro assays and provide an effective scaffold for drug design studies. Another goal of this project is to provide critical amino acid targets in the active site for future drug design studies. This study simulated 7.8 million drug candidates using high-throughput virtual screening and further processed the top scoring 241 molecules from AutoDock Vina, DOCK 6, and de novo design. Using virtual screening, de novo design, and molecular dynamics simulations, a competitive inhibitor candidate was discovered with an average binding free energy score of -46.03 kcal/mol, more than 10 kcal/mol better than the substrate control (dCMP). These results indicate that this molecule (or a structural derivative) may be an effective inhibitor of APOBEC3B and prevent host genome mutagenesis resulting from protein overexpression. Another important finding is the confirmation of essential amino acid targets, such as Tyr250 and Gln213 within the active site of APOBEC3B. Therefore, study used novel computational methods to provide a theoretical scaffold for future drug design studies that may prove useful as a treatment for epithelial cancers.Communicated by Ramaswamy H. Sarma.
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Investigating human development is a substantial scientific challenge due to the technical and ethical limitations of working with embryonic samples. In the face of these difficulties, stem cells have provided an alternative to experimentally model inaccessible stages of human development in vitro1-13. Here we show that human pluripotent stem cells can be triggered to self-organize into three-dimensional structures that recapitulate some key spatiotemporal events of early human post-implantation embryonic development. Our system reproducibly captures spontaneous differentiation and co-development of embryonic epiblast-like and extra-embryonic hypoblast-like lineages, establishes key signalling hubs with secreted modulators and undergoes symmetry breaking-like events. Single-cell transcriptomics confirms differentiation into diverse cell states of the perigastrulating human embryo14,15 without establishing placental cell types, including signatures of post-implantation epiblast, amniotic ectoderm, primitive streak, mesoderm, early extra-embryonic endoderm, as well as initial yolk sac induction. Collectively, our system captures key features of human embryonic development spanning from Carnegie stage16 4-7, offering a reproducible, tractable and scalable experimental platform to understand the basic cellular and molecular mechanisms that underlie human development, including new opportunities to dissect congenital pathologies with high throughput.
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Linhagem da Célula , Implantação do Embrião , Desenvolvimento Embrionário , Células-Tronco Pluripotentes , Feminino , Humanos , Gravidez , Diferenciação Celular , Camadas Germinativas/citologia , Camadas Germinativas/enzimologia , Células-Tronco Embrionárias Humanas/citologia , Placenta/citologia , Células-Tronco Pluripotentes/citologia , Linha Primitiva/citologia , Linha Primitiva/embriologia , Saco Vitelino/citologia , Saco Vitelino/embriologiaRESUMO
Repetitive DNA elements are packaged in heterochromatin, but many require bursts of transcription to initiate and maintain long-term silencing. The mechanisms by which these heterochromatic genome features are transcribed remain largely unknown. Here, we show that DOT1L, a conserved histone methyltransferase that modifies lysine 79 of histone H3 (H3K79), has a specialized role in transcription of major satellite repeats to maintain pericentromeric heterochromatin and genome stability. We find that H3K79me3 is selectively enriched relative to H3K79me2 at repetitive elements in mouse embryonic stem cells (mESCs), that DOT1L loss compromises pericentromeric satellite transcription, and that this activity involves possible coordination between DOT1L and the chromatin remodeler SMARCA5. Stimulation of transcript production from pericentromeric repeats by DOT1L participates in stabilization of heterochromatin structures in mESCs and cleavage-stage embryos and is required for preimplantation viability. Our findings uncover an important role for DOT1L as a bridge between transcriptional activation of repeat elements and heterochromatin stability, advancing our understanding of how genome integrity is maintained and how chromatin state is set up during early development.
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Heterocromatina , Metiltransferases , Animais , Camundongos , Cromatina/genética , Montagem e Desmontagem da Cromatina , Heterocromatina/genética , Histona Metiltransferases/genética , Histonas/metabolismo , Mamíferos/genética , Mamíferos/metabolismo , Metiltransferases/genética , Metiltransferases/metabolismoRESUMO
DNA and Histone 3 Lysine 27 methylation typically function as repressive modifications and operate within distinct genomic compartments. In mammals, the majority of the genome is kept in a DNA methylated state, whereas the Polycomb repressive complexes regulate the unmethylated CpG-rich promoters of developmental genes. In contrast to this general framework, the extra-embryonic lineages display non-canonical, globally intermediate DNA methylation levels, including disruption of local Polycomb domains. Here, to better understand this unusual landscape's molecular properties, we genetically and chemically perturbed major epigenetic pathways in mouse trophoblast stem cells. We find that the extra-embryonic epigenome reflects ongoing and dynamic de novo methyltransferase recruitment, which is continuously antagonized by Polycomb to maintain intermediate, locally disordered methylation. Despite its disorganized molecular appearance, our data point to a highly controlled equilibrium between counteracting repressors within extra-embryonic cells, one that can seemingly persist indefinitely without bistable features typically seen for embryonic forms of epigenetic regulation.
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Epigênese Genética , Epigenoma , Animais , Camundongos , Feminino , Gravidez , Epigenoma/genética , Placenta/metabolismo , Metilação de DNA , Proteínas do Grupo Polycomb/genética , DNA/metabolismo , Mamíferos/metabolismoRESUMO
Unique chromatin remodeling factors orchestrate dramatic changes in nuclear morphology during differentiation of the mature sperm head. A crucial step in this process is histone-to-protamine exchange, which must be executed correctly to avoid sperm DNA damage, embryonic lethality and male sterility. Here, we define an essential role for the histone methyltransferase DOT1L in the histone-to-protamine transition. We show that DOT1L is abundantly expressed in mouse meiotic and postmeiotic germ cells, and that methylation of histone H3 lysine 79 (H3K79), the modification catalyzed by DOT1L, is enriched in developing spermatids in the initial stages of histone replacement. Elongating spermatids lacking DOT1L fail to fully replace histones and exhibit aberrant protamine recruitment, resulting in deformed sperm heads and male sterility. Loss of DOT1L results in transcriptional dysregulation coinciding with the onset of histone replacement and affecting genes required for histone-to-protamine exchange. DOT1L also deposits H3K79me2 and promotes accumulation of elongating RNA Polymerase II at the testis-specific bromodomain gene Brdt. Together, our results indicate that DOT1L is an important mediator of transcription during spermatid differentiation and an indispensable regulator of male fertility.
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Histonas , Espermátides , Animais , Masculino , Camundongos , Diferenciação Celular/genética , Montagem e Desmontagem da Cromatina , Histona-Lisina N-Metiltransferase/genética , Histona-Lisina N-Metiltransferase/metabolismo , Histonas/metabolismo , Protaminas/genética , Protaminas/metabolismo , Sêmen/metabolismo , Espermátides/metabolismoRESUMO
Most endogenous retroviruses (ERVs) in mammals are incapable of retrotransposition; therefore, why ERV derepression is associated with lethality during early development has been a mystery. Here, we report that rapid and selective degradation of the heterochromatin adapter protein TRIM28 triggers dissociation of transcriptional condensates from loci encoding super-enhancer (SE)-driven pluripotency genes and their association with transcribed ERV loci in murine embryonic stem cells. Knockdown of ERV RNAs or forced expression of SE-enriched transcription factors rescued condensate localization at SEs in TRIM28-degraded cells. In a biochemical reconstitution system, ERV RNA facilitated partitioning of RNA polymerase II and the Mediator coactivator into phase-separated droplets. In TRIM28 knockout mouse embryos, single-cell RNA-seq analysis revealed specific depletion of pluripotent lineages. We propose that coding and noncoding nascent RNAs, including those produced by retrotransposons, may facilitate 'hijacking' of transcriptional condensates in various developmental and disease contexts.
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Retrovirus Endógenos , Animais , Células-Tronco Embrionárias , Retrovirus Endógenos/genética , Heterocromatina , Mamíferos/genética , Camundongos , Corpos Nucleares , RetroelementosRESUMO
Genomic imprinting and X chromosome inactivation (XCI) require epigenetic mechanisms to encode allele-specific expression, but how these specific tasks are accomplished at single loci or across chromosomal scales remains incompletely understood. Here, we systematically disrupt essential epigenetic pathways within polymorphic embryos in order to examine canonical and non-canonical genomic imprinting as well as XCI. We find that DNA methylation and Polycomb group repressors are indispensable for autosomal imprinting, albeit at distinct gene sets. Moreover, the extraembryonic ectoderm relies on a broader spectrum of imprinting mechanisms, including non-canonical targeting of maternal endogenous retrovirus (ERV)-driven promoters by the H3K9 methyltransferase G9a. We further identify Polycomb-dependent and -independent gene clusters on the imprinted X chromosome, which appear to reflect distinct domains of Xist-mediated suppression. From our data, we assemble a comprehensive inventory of the epigenetic pathways that maintain parent-specific imprinting in eutherian mammals, including an expanded view of the placental lineage.
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Linhagem da Célula/fisiologia , Ectoderma/metabolismo , Impressão Genômica/genética , Placenta/metabolismo , Animais , Metilação de DNA/fisiologia , Epigênese Genética/genética , Feminino , Histonas/metabolismo , Camundongos , Gravidez , RNA Longo não Codificante/genéticaRESUMO
The integration of DNA methylation and transcriptional state within single cells is of broad interest. Several single-cell dual- and multi-omics approaches have been reported that enable further investigation into cellular heterogeneity, including the discovery and in-depth study of rare cell populations. Such analyses will continue to provide important mechanistic insights into the regulatory consequences of epigenetic modifications. We recently reported a new method for profiling the DNA methylome and transcriptome from the same single cells in a cancer research study. Here, we present details of the protocol and provide guidance on its utility. Our Smart-RRBS (reduced representation bisulfite sequencing) protocol combines Smart-seq2 and RRBS and entails physically separating mRNA from the genomic DNA. It generates paired epigenetic promoter and RNA-expression measurements for ~24% of protein-coding genes in a typical single cell. It also works for micro-dissected tissue samples comprising hundreds of cells. The protocol, excluding flow sorting of cells and sequencing, takes ~3 d to process up to 192 samples manually. It requires basic molecular biology expertise and laboratory equipment, including a PCR workstation with UV sterilization, a DNA fluorometer and a microfluidic electrophoresis system.
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DNA/metabolismo , Análise de Célula Única , Sequência de Aminoácidos , Antibacterianos/farmacologia , DNA (Citosina-5-)-Metiltransferases/genética , DNA (Citosina-5-)-Metiltransferases/metabolismo , Doxiciclina/farmacologia , Epigenoma , Regulação da Expressão Gênica/efeitos dos fármacos , Regulação da Expressão Gênica/fisiologia , Humanos , Peptídeos e Proteínas de Sinalização Intracelular , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , TranscriptomaRESUMO
Serrated polyposis syndrome (SPS) is a pre-cancerous condition associated with increased risk of developing colorectal cancer (CRC). Its role in inflammatory bowel disease (IBD)-associated CRC remains unknown. Despite the growing understanding and recognition of SPS, there is limited literature about its impact on the colon in individuals with IBD. Herein, we report a case of a 45-year-old female who was diagnosed with ulcerative colitis (UC) and SPS. We also reviewed the literature surrounding this association and highlighted the intricacies in managing this unique patient population. At present, there are no screening guidelines for CRC in SPS patients with IBD. However, given the potential synergistic risk for CRC, a close surveillance approach may be utilized. Tracking lifetime cumulative features of SPS and endoscopic clearance of adenomas and serrated polyps are the mainstays of management.
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During ontogeny, proliferating cells become restricted in their fate through the combined action of cell-type-specific transcription factors and ubiquitous epigenetic machinery, which recognizes universally available histone residues or nucleotides in a context-dependent manner1,2. The molecular functions of these regulators are generally well understood, but assigning direct developmental roles to them is hampered by complex mutant phenotypes that often emerge after gastrulation3,4. Single-cell RNA sequencing and analytical approaches have explored this highly conserved, dynamic period across numerous model organisms5-8, including mouse9-18. Here we advance these strategies using a combined zygotic perturbation and single-cell RNA-sequencing platform in which many mutant mouse embryos can be assayed simultaneously, recovering robust morphological and transcriptional information across a panel of ten essential regulators. Deeper analysis of central Polycomb repressive complex (PRC) 1 and 2 components indicates substantial cooperativity, but distinguishes a dominant role for PRC2 in restricting the germline. Moreover, PRC mutant phenotypes emerge after gross epigenetic and transcriptional changes within the initial conceptus prior to gastrulation. Our experimental framework may eventually lead to a fully quantitative view of how cellular diversity emerges using an identical genetic template and from a single totipotent cell.
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Epigênese Genética , Gástrula/embriologia , Gástrula/metabolismo , Gastrulação/genética , Animais , Linhagem da Célula , Feminino , Gástrula/citologia , Regulação da Expressão Gênica no Desenvolvimento , Masculino , Camundongos , Mutação , Complexo Repressor Polycomb 1/metabolismo , Complexo Repressor Polycomb 2/metabolismo , Análise de Célula Única , Transcrição GênicaRESUMO
Mammalian cells stably maintain high levels of DNA methylation despite expressing both positive (DNMT3A/B) and negative (TET1-3) regulators. Here, we analyzed the independent and combined effects of these regulators on the DNA methylation landscape using a panel of knockout human embryonic stem cell (ESC) lines. The greatest impact on global methylation levels was observed in DNMT3-deficient cells, including reproducible focal demethylation at thousands of normally methylated loci. Demethylation depends on TET expression and occurs only when both DNMT3s are absent. Dynamic loci are enriched for hydroxymethylcytosine and overlap with subsets of putative somatic enhancers that are methylated in ESCs and can be activated upon differentiation. We observe similar dynamics in mouse ESCs that were less frequent in epiblast stem cells (EpiSCs) and scarce in somatic tissues, suggesting a conserved pluripotency-linked mechanism. Taken together, our data reveal tightly regulated competition between DNMT3s and TETs at thousands of somatic regulatory sequences within pluripotent cells.
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DNA (Citosina-5-)-Metiltransferases/genética , Metilação de DNA/genética , Elementos Facilitadores Genéticos/genética , Oxigenases de Função Mista/genética , Células-Tronco Pluripotentes/fisiologia , Proteínas Proto-Oncogênicas/genética , Animais , Diferenciação Celular/genética , Linhagem Celular , DNA Metiltransferase 3A , Células-Tronco Embrionárias/fisiologia , Epigênese Genética/genética , Regulação da Expressão Gênica no Desenvolvimento/genética , Camadas Germinativas/fisiologia , Humanos , Camundongos , Camundongos KnockoutRESUMO
Recent evidence has determined that the conserved X chromosome mega-structures controlled by the Firre and Dxz4 loci are not required for X chromosome inactivation (XCI) in cell lines. Here, we examined the in vivo contribution of these loci by generating mice carrying a single or double deletion of Firre and Dxz4. We found that these mutants are viable, fertile and show no defect in random or imprinted XCI. However, the lack of these elements results in many dysregulated genes on autosomes in an organ-specific manner. By comparing the dysregulated genes between the single and double deletion, we identified superloop, megadomain, and Firre locus-dependent gene sets. The largest transcriptional effect was observed in all strains lacking the Firre locus, indicating that this locus is the main driver for these autosomal expression signatures. Collectively, these findings suggest that these X-linked loci are involved in autosomal gene regulation rather than XCI biology.
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DNA Complementar/genética , Deleção de Genes , Regulação da Expressão Gênica , RNA Longo não Codificante/genética , Animais , Feminino , Masculino , Camundongos , Camundongos Endogâmicos , Camundongos Knockout , Transcriptoma , Inativação do Cromossomo XRESUMO
Ectopic transcription factor expression enables reprogramming of somatic cells to pluripotency, albeit with generally low efficiency. Despite steady progress in the field, the exact molecular mechanisms that coordinate this remarkable transition still remain largely elusive. To better characterize the final steps of pluripotency induction, we optimized an experimental system where pluripotent stem cells are differentiated for set intervals before being reintroduced to pluripotency-supporting conditions. Using this approach, we identify a transient period of high-efficiency reprogramming where ectopic transcription factors, but not serum/LIF alone, rapidly revert cells to pluripotency with near 100% efficiency. After this period, cells reprogram with somatic-like kinetics and efficiencies. We identify a set of OCT4 bound cis-regulatory elements that are dynamically regulated during this transient phase and appear central to facilitating reprogramming. Interestingly, these regions remain hypomethylated during in vitro and in vivo differentiation, which may allow them to act as primary targets of ectopically induced factors during somatic cell reprogramming.
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Diferenciação Celular/fisiologia , Reprogramação Celular/fisiologia , Células-Tronco Pluripotentes Induzidas/metabolismo , Fator 3 de Transcrição de Octâmero/metabolismo , Fatores de Transcrição/metabolismo , Animais , Linhagem Celular , Fibroblastos , Regulação da Expressão Gênica , Genômica , Cinética , Camundongos , Proteína Homeobox Nanog , Fator 3 de Transcrição de Octâmero/genética , Células-TroncoRESUMO
Maintenance of pluripotency and specification towards a new cell fate are both dependent on precise interactions between extrinsic signals and transcriptional and epigenetic regulators. Directed methylation of cytosines by the de novo methyltransferases DNMT3A and DNMT3B plays an important role in facilitating proper differentiation, whereas DNMT1 is essential for maintaining global methylation levels in all cell types. Here, we generated single-cell mRNA expression data from wild-type, DNMT3A, DNMT3A/3B and DNMT1 knockout human embryonic stem cells and observed a widespread increase in cellular and transcriptional variability, even with limited changes in global methylation levels in the de novo knockouts. Furthermore, we found unexpected transcriptional repression upon either loss of the de novo methyltransferase DNMT3A or the double knockout of DNMT3A/3B that is further propagated upon differentiation to mesoderm and ectoderm. Taken together, our single-cell RNA-sequencing data provide a high-resolution view into the consequences of depleting the three catalytically active DNMTs in human pluripotent stem cells.
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DNA (Citosina-5-)-Metiltransferase 1/metabolismo , DNA (Citosina-5-)-Metiltransferases/metabolismo , Células-Tronco Embrionárias Humanas/metabolismo , Proteínas Repressoras/metabolismo , Transcrição Gênica , Ciclo Celular/genética , Diferenciação Celular/genética , Metilação de DNA/genética , DNA Metiltransferase 3A , Elementos Facilitadores Genéticos/genética , Entropia , Regulação da Expressão Gênica no Desenvolvimento , Humanos , Masculino , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , DNA Metiltransferase 3BRESUMO
Ontogeny describes the emergence of complex multicellular organisms from single totipotent cells. This field is particularly challenging in mammals, owing to the indeterminate relationship between self-renewal and differentiation, variation in progenitor field sizes, and internal gestation in these animals. Here we present a flexible, high-information, multi-channel molecular recorder with a single-cell readout and apply it as an evolving lineage tracer to assemble mouse cell-fate maps from fertilization through gastrulation. By combining lineage information with single-cell RNA sequencing profiles, we recapitulate canonical developmental relationships between different tissue types and reveal the nearly complete transcriptional convergence of endodermal cells of extra-embryonic and embryonic origins. Finally, we apply our cell-fate maps to estimate the number of embryonic progenitor cells and their degree of asymmetric partitioning during specification. Our approach enables massively parallel, high-resolution recording of lineage and other information in mammalian systems, which will facilitate the construction of a quantitative framework for understanding developmental processes.
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Embrião de Mamíferos/embriologia , Embrião de Mamíferos/metabolismo , Desenvolvimento Embrionário/genética , Animais , Diferenciação Celular/genética , Linhagem da Célula/genética , Embrião de Mamíferos/citologia , Células-Tronco Embrionárias/citologia , Células-Tronco Embrionárias/metabolismo , Endoderma/embriologia , Endoderma/metabolismo , Feminino , Fertilização , Gastrulação , Regulação da Expressão Gênica no Desenvolvimento/genética , Masculino , Camundongos , Especificidade de Órgãos/genética , Fenótipo , Análise de Sequência de RNA , Análise de Célula ÚnicaRESUMO
DNA methylation plays an essential role in mammalian genomes and expression of the responsible enzymes is tightly controlled. Deregulation of the de novo DNA methyltransferase DNMT3B is frequently observed across cancer types, yet little is known about its ectopic genomic targets. Here, we used an inducible transgenic mouse model to delineate rules for abnormal DNMT3B targeting, as well as the constraints of its activity across different cell types. Our results explain the preferential susceptibility of certain CpG islands to aberrant methylation and point to transcriptional state and the associated chromatin landscape as the strongest predictors. Although DNA methylation and H3K27me3 are usually non-overlapping at CpG islands, H3K27me3 can transiently co-occur with DNMT3B-induced DNA methylation. Our genome-wide data combined with ultra-deep locus-specific bisulfite sequencing suggest a distributive activity of ectopically expressed Dnmt3b that leads to discordant CpG island hypermethylation and provides new insights for interpreting the cancer methylome.