RESUMO
Current human pluripotent stem cells lack the transcription factor circuitry that governs the ground state of mouse embryonic stem cells (ESC). Here, we report that short-term expression of two components, NANOG and KLF2, is sufficient to ignite other elements of the network and reset the human pluripotent state. Inhibition of ERK and protein kinase C sustains a transgene-independent rewired state. Reset cells self-renew continuously without ERK signaling, are phenotypically stable, and are karyotypically intact. They differentiate in vitro and form teratomas in vivo. Metabolism is reprogrammed with activation of mitochondrial respiration as in ESC. DNA methylation is dramatically reduced and transcriptome state is globally realigned across multiple cell lines. Depletion of ground-state transcription factors, TFCP2L1 or KLF4, has marginal impact on conventional human pluripotent stem cells but collapses the reset state. These findings demonstrate feasibility of installing and propagating functional control circuitry for ground-state pluripotency in human cells.
Assuntos
Proteínas de Homeodomínio/metabolismo , Fatores de Transcrição Kruppel-Like/metabolismo , Células-Tronco Pluripotentes/metabolismo , Animais , Técnicas Citológicas , Células-Tronco Embrionárias/citologia , Células-Tronco Embrionárias/metabolismo , Epigênese Genética , Humanos , Fator 4 Semelhante a Kruppel , Camundongos , Mitocôndrias/metabolismo , Proteína Homeobox Nanog , Células-Tronco Pluripotentes/citologia , Fatores de Transcrição/metabolismo , TranscriptomaRESUMO
Aging is associated with an abnormal increase in DNA methylation (DNAm) in human gene promoters, including in bone marrow stem cells. DNAm patterns are further perturbed in hematological malignancies such as acute myeloid leukemia but the physiological significance of such epigenetic changes is unknown. Using epigenetic editing of human stem/progenitor cells (HSPCs), we show that p15 methylation affects hematopoiesis in vivo. We edited the CDKN2B (p15) promoter and ARF (p14) using dCas9-3A3L and observed DNAm spreading beyond the gRNA location. We find that despite a transient delivery system, DNAm is maintained during myeloid differentiation in vitro, and hypermethylation of the p15 promoter reduces gene expression. In vivo, edited human HSPCs can engraft the bone marrow of mice and targeted DNAm is maintained in HSPCs long term. Moreover, epigenetic changes are conserved and inherited in both myeloid and lymphoid lineages. Although the proportion of myeloid (CD33+) and lymphoid (CD19+) cells is unaffected, monocyte (CD14+) populations decreased and granulocytes (CD66b+) increased in mice engrafted with p15 hypermethylated HSPCs. Monocytes derived from p15 hypermethylated HSPCs appear to be activated and show increased inflammatory transcriptional programs. We believe these findings have clinical relevance since we found p15 promoter methylation in the peripheral blood of patients with clonal hematopoiesis. Our study shows DNAm can be targeted and maintained in human HSPCs and demonstrated functional relevance of aberrant DNAm on the p15 locus. As such, other aging-associated aberrant DNAm may impact hematopoiesis in vivo.
Assuntos
Metilação de DNA , Leucemia Mieloide Aguda , Humanos , Repetições Palindrômicas Curtas Agrupadas e Regularmente Espaçadas , Hematopoese/genética , Leucemia Mieloide Aguda/genética , Regiões Promotoras GenéticasRESUMO
Transcription factors (TFs) are proteins that affect gene expression by binding to regulatory regions of DNA in a sequence specific manner. The binding of TFs to DNA is controlled by many factors, including the DNA sequence, concentration of TF, chromatin accessibility and co-factors. Here, we systematically investigated the binding mechanism of hundreds of TFs by analysing ChIP-seq data with our explainable statistical model, ChIPanalyser. This tool uses as inputs the DNA sequence binding motif; the capacity to distinguish between strong and weak binding sites; the concentration of TF; and chromatin accessibility. We found that approximately one third of TFs are predicted to bind the genome in a DNA accessibility independent fashion, which includes TFs that can open the chromatin, their co-factors and TFs with similar motifs. Our model predicted this to be the case when the TF binds to its strongest binding regions in the genome, and only a small number of TFs have the capacity to bind dense chromatin at their weakest binding regions, such as CTCF, USF2 and CEBPB. Our study demonstrated that the binding of hundreds of human and mouse TFs is predicted by ChIPanalyser with high accuracy and showed that many TFs can bind dense chromatin.
Assuntos
Cromatina , Fatores de Transcrição , Humanos , Animais , Camundongos , Cromatina/genética , Fatores de Transcrição/metabolismo , Cromossomos/metabolismo , DNA/química , Sítios de Ligação/genética , Ligação Proteica , Mamíferos/genéticaRESUMO
Pluripotent cells, when fused with somatic cells, have the dominant ability to reprogram the somatic genome. Work by Piccolo et al. (2013) shows that the Tet1 and Tet2 hydroxylases are important for DNA methylation reprogramming of pluripotency genes and parental imprints.
RESUMO
To identify genomic alterations contributing to the pathogenesis of high-risk chronic lymphocytic leukemia (CLL) beyond the well-established role of TP53 aberrations, we comprehensively analyzed 75 relapsed/refractory and 71 treatment-naïve high-risk cases from prospective clinical trials by single nucleotide polymorphism arrays and targeted next-generation sequencing. Increased genomic complexity was a hallmark of relapsed/refractory and treatment-naïve high-risk CLL. In relapsed/refractory cases previously exposed to the selective pressure of chemo(immuno)therapy, gain(8)(q24.21) and del(9)(p21.3) were particularly enriched. Both alterations affect key regulators of cell-cycle progression, namely MYC and CDKN2A/B While homozygous CDKN2A/B loss has been directly associated with Richter transformation, we did not find this association for heterozygous loss of CDKN2A/B Gains in 8q24.21 were either focal gains in a MYC enhancer region or large gains affecting the MYC locus, but only the latter type was highly enriched in relapsed/refractory CLL (17%). In addition to a high frequency of NOTCH1 mutations (23%), we found recurrent genetic alterations in SPEN (4% mutated), RBPJ (8% deleted) and SNW1 (8% deleted), all affecting a protein complex that represses transcription of NOTCH1 target genes. We investigated the functional impact of these alterations on HES1, DTX1 and MYC gene transcription and found derepression of these NOTCH1 target genes particularly with SPEN mutations. In summary, we provide new insights into the genomic architecture of high-risk CLL, define novel recurrent DNA copy number alterations and refine knowledge on del(9p), gain(8q) and alterations affecting NOTCH1 signaling. This study was registered at ClinicalTrials.gov with number NCT01392079.
Assuntos
Leucemia Linfocítica Crônica de Células B , Receptor Notch1/genética , Ciclo Celular , Genômica , Humanos , Leucemia Linfocítica Crônica de Células B/genética , Mutação , Estudos ProspectivosRESUMO
Epigenetic memory, in particular DNA methylation, is established during development in differentiating cells and must be erased to create naïve (induced) pluripotent stem cells. The ten-eleven translocation (TET) enzymes can catalyze the oxidation of 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC) and further oxidized derivatives, thereby actively removing this memory. Nevertheless, the mechanism by which the TET enzymes are regulated, and the extent to which they can be manipulated, are poorly understood. Here we report that retinoic acid (RA) or retinol (vitamin A) and ascorbate (vitamin C) act as modulators of TET levels and activity. RA or retinol enhances 5hmC production in naïve embryonic stem cells by activation of TET2 and TET3 transcription, whereas ascorbate potentiates TET activity and 5hmC production through enhanced Fe2+ recycling, and not as a cofactor as reported previously. We find that both ascorbate and RA or retinol promote the derivation of induced pluripotent stem cells synergistically and enhance the erasure of epigenetic memory. This mechanistic insight has significance for the development of cell treatments for regenenerative medicine, and enhances our understanding of how intrinsic and extrinsic signals shape the epigenome.
Assuntos
Diferenciação Celular/efeitos dos fármacos , Proteínas de Ligação a DNA/genética , Dioxigenases/genética , Células-Tronco Pluripotentes Induzidas/metabolismo , Proteínas Proto-Oncogênicas/genética , 5-Metilcitosina/metabolismo , Animais , Ácido Ascórbico/farmacologia , Metilação de DNA/efeitos dos fármacos , Metilação de DNA/genética , Epigênese Genética/efeitos dos fármacos , Humanos , Células-Tronco Pluripotentes Induzidas/citologia , Camundongos , Medicina Regenerativa , Tretinoína/farmacologia , Vitamina A/farmacologiaRESUMO
DNA methylation and demethylation are opposing processes that when in balance create stable patterns of epigenetic memory. The control of DNA methylation pattern formation by replication dependent and independent demethylation processes has been suggested to be influenced by Tet mediated oxidation of 5mC. Several alternative mechanisms have been proposed suggesting that 5hmC influences either replication dependent maintenance of DNA methylation or replication independent processes of active demethylation. Using high resolution hairpin oxidative bisulfite sequencing data, we precisely determine the amount of 5mC and 5hmC and model the contribution of 5hmC to processes of demethylation in mouse ESCs. We develop an extended hidden Markov model capable of accurately describing the regional contribution of 5hmC to demethylation dynamics. Our analysis shows that 5hmC has a strong impact on replication dependent demethylation, mainly by impairing methylation maintenance.
Assuntos
Ilhas de CpG , Metilação de DNA , Modelos Biológicos , 5-Metilcitosina/análogos & derivados , 5-Metilcitosina/metabolismo , Animais , Divisão Celular , Biologia Computacional , Replicação do DNA , Células-Tronco Embrionárias/metabolismo , Hidroxilação , Cadeias de Markov , Camundongos , Processos Estocásticos , Sulfitos/metabolismoRESUMO
Just over 2 years ago, TET1 was found to catalyse the oxidation of 5-methylcytosine, a well-known epigenetic mark, into 5-hydroxymethylcytosine in mammalian DNA. The exciting prospect of a novel epigenetic modification that may dynamically regulate DNA methylation has led to the rapid accumulation of publications from a wide array of fields, from biochemistry to stem cell biology. Although we have only started to scratch the surface, interesting clues on the role of 5-hydroxymethylcytosine are quickly emerging.
Assuntos
Citosina/análogos & derivados , Proteínas de Ligação a DNA , Epigênese Genética/genética , Epigenômica/métodos , Proteínas Proto-Oncogênicas , 5-Metilcitosina/metabolismo , Animais , Massa Celular Interna do Blastocisto/metabolismo , Diferenciação Celular/genética , Proliferação de Células , Cromatina/metabolismo , Ilhas de CpG/fisiologia , Citosina/metabolismo , DNA/genética , DNA/metabolismo , Metilação de DNA/genética , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/metabolismo , Desaminação/genética , Dioxigenases , Células-Tronco Embrionárias/citologia , Células-Tronco Embrionárias/enzimologia , Regulação da Expressão Gênica no Desenvolvimento , Inativação Gênica/fisiologia , Genoma/genética , Hematopoese/genética , Humanos , Camundongos , Camundongos Knockout , Oxigenases de Função Mista , Proteínas Proto-Oncogênicas/genética , Proteínas Proto-Oncogênicas/metabolismo , Distribuição Tecidual/genéticaRESUMO
Methylation at the 5' position of cytosine in DNA has important roles in genome function and is dynamically reprogrammed during early embryonic and germ cell development. The mammalian genome also contains 5-hydroxymethylcytosine (5hmC), which seems to be generated by oxidation of 5-methylcytosine (5mC) by the TET family of enzymes that are highly expressed in embryonic stem (ES) cells. Here we use antibodies against 5hmC and 5mC together with high throughput sequencing to determine genome-wide patterns of methylation and hydroxymethylation in mouse wild-type and mutant ES cells and differentiating embryoid bodies. We find that 5hmC is mostly associated with euchromatin and that whereas 5mC is under-represented at gene promoters and CpG islands, 5hmC is enriched and is associated with increased transcriptional levels. Most, if not all, 5hmC in the genome depends on pre-existing 5mC and the balance between these two modifications is different between genomic regions. Knockdown of Tet1 and Tet2 causes downregulation of a group of genes that includes pluripotency-related genes (including Esrrb, Prdm14, Dppa3, Klf2, Tcl1 and Zfp42) and a concomitant increase in methylation of their promoters, together with an increased propensity of ES cells for extraembryonic lineage differentiation. Declining levels of TETs during differentiation are associated with decreased hydroxymethylation levels at the promoters of ES cell-specific genes together with increased methylation and gene silencing. We propose that the balance between hydroxymethylation and methylation in the genome is inextricably linked with the balance between pluripotency and lineage commitment.
Assuntos
Diferenciação Celular/genética , Citosina/análogos & derivados , Metilação de DNA , Células-Tronco Embrionárias/citologia , Células-Tronco Embrionárias/metabolismo , Regulação da Expressão Gênica no Desenvolvimento , 5-Metilcitosina/análogos & derivados , Animais , Anticorpos/imunologia , Linhagem Celular , Linhagem da Célula/genética , Ilhas de CpG/genética , Citosina/análise , Citosina/imunologia , Citosina/metabolismo , Proteínas de Ligação a DNA/deficiência , Dioxigenases , Regulação para Baixo , Corpos Embrioides/citologia , Corpos Embrioides/metabolismo , Eucromatina/genética , Eucromatina/metabolismo , Éxons/genética , Inativação Gênica , Genoma/genética , Camundongos , Células-Tronco Pluripotentes/citologia , Células-Tronco Pluripotentes/metabolismo , Regiões Promotoras Genéticas/genética , Proteínas Proto-Oncogênicas/deficiência , Reprodutibilidade dos Testes , Análise de Sequência de DNA , Transcrição GênicaRESUMO
From a fertilised egg to a mature organism, cells divide and accumulate epigenetic information, which is faithfully passed on to daughter cells. DNA methylation consolidates the memory of the developmental history and, albeit very stable, it is not immutable and DNA methylation patterns can be deconstructed a process that is essential to regain totipotency. Research into DNA methylation erasure gained momentum a few years ago with the discovery of 5-hydroxymethylcytosine, an oxidation product of 5-methylcytosine. The role of this new epigenetic modification in DNA demethylation and other potential epigenetic roles are discussed here. But what are the mechanisms that regulate deposition of epigenetic modifications? Until recently, limited direct evidence indicated that signalling molecules are able to modulate the function of epigenetic modifiers, which shape the epigenome in the nucleus of the cell. New reports in embryonic stem cell model systems disclosed a tight relationship between major signalling pathways and the DNA methylation machinery, which opens up exciting avenues in the relationship between external signals and epigenetic memory. Here, I discuss mechanisms and concepts in DNA methylation patterning, the implications in normal development and disease, and future directions.
Assuntos
Metilação de DNA/genética , Animais , Diferenciação Celular , Reprogramação Celular/genética , Cromatina/metabolismo , DNA/metabolismo , Epigenômica , Humanos , Modelos BiológicosRESUMO
Discovery of the enzymatic activity that catalyses oxidation of 5-methylcytosine (5mC) to generate 5-hydroxymethylcytosine (5hmC) mediated by the MLL (KMT2A) fusion partner TET1 has sparked intense research to understand the role this new DNA modification has in cancer. An unambiguous picture has emerged where tumours are depleted of 5hmC compared to corresponding normal tissue, but it is not known whether lack of 5hmC is a cause or a consequence of tumourigenesis. Experimental data reveals a dual tumour-suppressive and oncogenic role for TET proteins. Tet2 mutations are drivers in haematological malignancies but Tet1 had an oncogenic role in MLL-rearranged leukaemia, where Tet1 is overexpressed. Overexpression of Tet2 in melanoma cells re-established the 5hmC landscape and suppressed cancer progression but inhibiting Tet1 in non-transformed cells did not initiate cellular transformation. In this review we summarise recent findings that have shaped the current understanding on the role 5hmC plays in cancer.
Assuntos
5-Metilcitosina/metabolismo , Citosina/análogos & derivados , Neoplasias/genética , Animais , Citosina/metabolismo , Metilação de DNA , DNA de Neoplasias/química , Proteínas de Ligação a DNA/genética , Dioxigenases , Humanos , Oxigenases de Função Mista , Oxirredução , Proteínas Proto-Oncogênicas/genéticaRESUMO
Overexpression of the HER2 protein in breast cancer patients is a predictor of poor prognosis and resistance to therapies. We used an inducible breast cancer transformation system that allows investigation of early molecular changes. HER2 overexpression to similar levels as those observed in a subtype of HER2-positive breast cancer patients induced transformation of MCF10A cells and resulted in gross morphological changes, increased anchorage-independent growth of cells, and altered the transcriptional programme of genes associated with oncogenic transformation. Global phosphoproteomic analysis during HER2 induction predominantly detected an increase in protein phosphorylation. Intriguingly, this correlated with chromatin opening, as measured by ATAC-seq on acini isolated from 3D cell culture. HER2 overexpression resulted in opening of many distal regulatory regions and promoted reprogramming-associated heterogeneity. We found that a subset of cells acquired a dedifferentiated breast stem-like phenotype, making them likely candidates for malignant transformation. Our data show that this population of cells, which counterintuitively enriches for relatively low HER2 protein abundance and increased chromatin accessibility, possesses transformational drive, resulting in increased anchorage-independent growth in vitro compared to cells not displaying a stem-like phenotype.
Assuntos
Cromatina , Receptor ErbB-2 , Humanos , Receptor ErbB-2/genética , Proliferação de Células , Transformação Celular Neoplásica/genética , Epitélio/metabolismo , Linhagem Celular Tumoral , Regulação Neoplásica da Expressão GênicaRESUMO
BACKGROUND: Vitamin C (vitC) enhances the activity of 2-oxoglutarate-dependent dioxygenases, including TET enzymes, which catalyse DNA demethylation, and Jumonji-domain histone demethylases. The epigenetic remodelling promoted by vitC improves the efficiency of induced pluripotent stem cell derivation, and is required to attain a ground-state of pluripotency in embryonic stem cells (ESCs) that closely mimics the inner cell mass of the early blastocyst. However, genome-wide DNA and histone demethylation can lead to upregulation of transposable elements (TEs), and it is not known how vitC addition in culture media affects TE expression in pluripotent stem cells. RESULTS: Here we show that vitC increases the expression of several TE families, including evolutionarily young LINE-1 (L1) elements, in mouse ESCs. We find that TET activity is dispensable for L1 upregulation, and that instead it occurs largely as a result of H3K9me3 loss mediated by KDM4A/C histone demethylases. Despite increased L1 levels, we did not detect increased somatic insertion rates in vitC-treated cells. Notably, treatment of human ESCs with vitC also increases L1 protein levels, albeit through a distinct, post-transcriptional mechanism. CONCLUSION: VitC directly modulates the expression of mouse L1s and other TEs through epigenetic mechanisms, with potential for downstream effects related to the multiple emerging roles of L1s in cellular function.
Assuntos
Ácido Ascórbico , Células-Tronco Embrionárias Murinas , Humanos , Animais , Camundongos , Ácido Ascórbico/farmacologia , Células-Tronco Embrionárias Murinas/metabolismo , Elementos Nucleotídeos Longos e Dispersos , Metilação de DNA , Histona Desmetilases/metabolismo , DNA/metabolismo , Desmetilação , Histona Desmetilases com o Domínio Jumonji/genética , Histona Desmetilases com o Domínio Jumonji/metabolismoRESUMO
Cancers are genetically divergent but intriguingly display similar patterns of epigenetic deregulation, including global DNA hypomethylation and hypermethylation of promoter CpG islands. Early developmental programmes mirror this cancer epigenome suggesting that reactivation of embryonic programmes is essential to the initiation of cancer. We propose a scenario where two waves of dedifferentiation underlie key cell transitions: the first from normal to cancer, and the second driving malignancy. The possibility that early developmental programmes underpin both normal development and the switch to cancer has huge therapeutic implications. The reignition of embryonic programmes and pluripotency networks in seemingly healthy tissues could provide unique cellular targets, to eliminate pre-cancerous or cancer promoting cells before they have the opportunity to form tumours. We conclude that focusing on epigenetic gatekeepers, and peri-implantation cellular identities, could transform the diagnosis and prevention of cancer, especially if these programmes crosscut many cancer types, solid and haematological.
Assuntos
Metilação de DNA , Neoplasias , Ilhas de CpG , Epigênese Genética , Humanos , Neoplasias/genética , Regiões Promotoras GenéticasRESUMO
Propagation of DNA methylation through cell division relies on the recognition of methylated cytosines by UHRF1. In reprogramming of mouse embryonic stem cells to naive pluripotency (also known as ground state), despite high levels of Uhrf1 transcript, the protein is targeted for degradation by the proteasome, leading to DNA methylation loss. We have undertaken an shRNA screen to identify the signalling pathways that converge upon UHRF1 and control its degradation, using UHRF1-GFP fluorescence as readout. Many candidates we identified are key enzymes in regulation of glucose metabolism, nucleotide metabolism and Pi3K/AKT/mTOR pathway. Unexpectedly, while downregulation of all candidates we selected for validation rescued UHRF1 protein levels, we found that in some of the cases this was not sufficient to maintain DNA methylation. This has implications for development, ageing and diseased conditions. Our study demonstrates two separate processes that regulate UHRF1 protein abundance and activity.
Assuntos
Metilação de DNA , Células-Tronco Embrionárias Murinas , Animais , Camundongos , Células-Tronco Embrionárias Murinas/metabolismo , Proteínas Estimuladoras de Ligação a CCAAT/genética , Proteínas Estimuladoras de Ligação a CCAAT/metabolismo , RNA Interferente Pequeno/metabolismo , Complexo de Endopeptidases do Proteassoma/genética , Complexo de Endopeptidases do Proteassoma/metabolismo , Ubiquitina-Proteína Ligases/genética , Ubiquitina-Proteína Ligases/metabolismo , Fosfatidilinositol 3-Quinases/genética , Proteínas Proto-Oncogênicas c-akt/genética , Serina-Treonina Quinases TOR/genética , Serina-Treonina Quinases TOR/metabolismo , Glucose/metabolismo , Nucleotídeos/metabolismoRESUMO
A precise understanding of DNA methylation dynamics is of great importance for a variety of biological processes including cellular reprogramming and differentiation. To date, complex integration of multiple and distinct genome-wide datasets is required to realize this task. We present GwEEP (genome-wide epigenetic efficiency profiling) a versatile approach to infer dynamic efficiencies of DNA modifying enzymes. GwEEP relies on genome-wide hairpin datasets, which are translated by a hidden Markov model into quantitative enzyme efficiencies with reported confidence around the estimates. GwEEP predicts de novo and maintenance methylation efficiencies of Dnmts and furthermore the hydroxylation efficiency of Tets. Its design also allows capturing further oxidation processes given available data. We show that GwEEP predicts accurately the epigenetic changes of ESCs following a Serum-to-2i shift and applied to Tet TKO cells confirms the hypothesized mutual interference between Dnmts and Tets.
Assuntos
Proteínas de Ligação a DNA , Epigênese Genética , Proteínas de Ligação a DNA/genética , Metilação de DNA/genética , DNA/genética , Diferenciação CelularRESUMO
DNA methylation patterns are reprogrammed in primordial germ cells and in preimplantation embryos by demethylation and subsequent de novo methylation. It has been suggested that epigenetic reprogramming may be necessary for the embryonic genome to return to a pluripotent state. We have carried out a genome-wide promoter analysis of DNA methylation in mouse embryonic stem (ES) cells, embryonic germ (EG) cells, sperm, trophoblast stem (TS) cells, and primary embryonic fibroblasts (pMEFs). Global clustering analysis shows that methylation patterns of ES cells, EG cells, and sperm are surprisingly similar, suggesting that while the sperm is a highly specialized cell type, its promoter epigenome is already largely reprogrammed and resembles a pluripotent state. Comparisons between pluripotent tissues and pMEFs reveal that a number of pluripotency related genes, including Nanog, Lefty1 and Tdgf1, as well as the nucleosome remodeller Smarcd1, are hypomethylated in stem cells and hypermethylated in differentiated cells. Differences in promoter methylation are associated with significant differences in transcription levels in more than 60% of genes analysed. Our comparative approach to promoter methylation thus identifies gene candidates for the regulation of pluripotency and epigenetic reprogramming. While the sperm genome is, overall, similarly methylated to that of ES and EG cells, there are some key exceptions, including Nanog and Lefty1, that are highly methylated in sperm. Nanog promoter methylation is erased by active and passive demethylation after fertilisation before expression commences in the morula. In ES cells the normally active Nanog promoter is silenced when targeted by de novo methylation. Our study suggests that reprogramming of promoter methylation is one of the key determinants of the epigenetic regulation of pluripotency genes. Epigenetic reprogramming in the germline prior to fertilisation and the reprogramming of key pluripotency genes in the early embryo is thus crucial for transmission of pluripotency.
Assuntos
Reprogramação Celular , Metilação de DNA , Epigênese Genética , Regulação da Expressão Gênica no Desenvolvimento , Proteínas de Homeodomínio/genética , Regiões Promotoras Genéticas , Células-Tronco/fisiologia , Animais , Células Cultivadas , Proteínas Cromossômicas não Histona/genética , Proteínas Cromossômicas não Histona/metabolismo , Fator de Crescimento Epidérmico/genética , Fator de Crescimento Epidérmico/metabolismo , Feminino , Genoma , Proteínas de Homeodomínio/metabolismo , Fatores de Determinação Direita-Esquerda , Masculino , Glicoproteínas de Membrana/genética , Glicoproteínas de Membrana/metabolismo , Proteínas de Membrana/genética , Proteínas de Membrana/metabolismo , Camundongos , Camundongos Endogâmicos , Análise em Microsséries , Proteína Homeobox Nanog , Proteínas de Neoplasias/genética , Proteínas de Neoplasias/metabolismo , Células-Tronco Pluripotentes/fisiologia , Espermatozoides/fisiologia , Fator de Crescimento Transformador beta/genética , Fator de Crescimento Transformador beta/metabolismoRESUMO
Chromatin configuration influences gene expression in eukaryotes at multiple levels, from individual nucleosomes to chromatin domains several Mb long. Post-translational modifications (PTM) of core histones seem to be involved in chromatin structural transitions, but how remains unclear. To explore this, we used ChIP-seq and two cell types, HeLa and lymphoblastoid (LCL), to define how changes in chromatin packaging through the cell cycle influence the distributions of three transcription-associated histone modifications, H3K9ac, H3K4me3 and H3K27me3. We show that chromosome regions (bands) of 10-50 Mb, detectable by immunofluorescence microscopy of metaphase (M) chromosomes, are also present in G1 and G2. They comprise 1-5 Mb sub-bands that differ between HeLa and LCL but remain consistent through the cell cycle. The same sub-bands are defined by H3K9ac and H3K4me3, while H3K27me3 spreads more widely. We found little change between cell cycle phases, whether compared by 5 Kb rolling windows or when analysis was restricted to functional elements such as transcription start sites and topologically associating domains. Only a small number of genes showed cell-cycle related changes: at genes encoding proteins involved in mitosis, H3K9 became highly acetylated in G2M, possibly because of ongoing transcription. In conclusion, modified histone isoforms H3K9ac, H3K4me3 and H3K27me3 exhibit a characteristic genomic distribution at resolutions of 1 Mb and below that differs between HeLa and lymphoblastoid cells but remains remarkably consistent through the cell cycle. We suggest that this cell-type-specific chromosomal bar-code is part of a homeostatic mechanism by which cells retain their characteristic gene expression patterns, and hence their identity, through multiple mitoses.
Assuntos
Cromossomos/genética , Epigênese Genética , Código das Histonas/genética , Processamento de Proteína Pós-Traducional/genética , Acetilação , Ciclo Celular , Cromatina/genética , Células HeLa , Histonas/genética , Humanos , Lisina , Metilação , Mitose/genética , Nucleossomos/genéticaRESUMO
The desire to analyse limited amounts of biological material, historic samples and rare cell populations has collectively driven the need for efficient methods for whole genome sequencing (WGS) of limited amounts of poor quality DNA. Most protocols are designed to recover double-stranded DNA (dsDNA) by ligating sequencing adaptors to dsDNA with or without subsequent polymerase chain reaction amplification of the library. While this is sufficient for many applications, limited DNA requires a method that can recover both single-stranded DNA (ssDNA) and dsDNA. Here, we present a WGS library preparation method, called 'degraded DNA adaptor tagging' (DDAT), adapted from a protocol designed for whole genome bisulfite sequencing. This method uses two rounds of random primer extension to recover both ssDNA and dsDNA. We show that by using DDAT we can generate WGS data from formalin-fixed paraffin-embedded (FFPE) samples using as little as 2 ng of highly degraded DNA input. Furthermore, DDAT WGS data quality was higher for all FFPE samples tested compared to data produced using a standard WGS library preparation method. Therefore, the DDAT method has potential to unlock WGS data from DNA previously considered impossible to sequence, broadening opportunities to understand the role of genetics in health and disease.