bims-crepig Biomed News
on Chromatin regulation and epigenetics in cell fate and cancer
Issue of 2021‒02‒28
nineteen papers selected by
Connor Rogerson
University of Cambridge, MRC Cancer Unit
  1. Single-cell multiomics sequencing reveals the functional regulatory landscape of early embryos.
  2. The Transcription Factor MAFF Regulates an Atherosclerosis Relevant Network Connecting Inflammation and Cholesterol Metabolism.
  3. Role of CxxC-finger protein 1 in establishing mouse oocyte epigenetic landscapes.
  4. FoxA-dependent demethylation of DNA initiates epigenetic memory of cellular identity.
  5. Depletion of H3K36me2 recapitulates epigenomic and phenotypic changes induced by the H3.3K36M oncohistone mutation.
  6. Annotation of chromatin states in 66 complete mouse epigenomes during development.
  7. Forkhead transcription factor Fkh1: insights into functional regulatory domains crucial for recruitment of Sin3 histone deacetylase complex.
  8. Distinct properties and functions of CTCF revealed by a rapidly inducible degron system.
  9. Iterative epigenomic analyses in the same single cell.
  10. A unique histone 3 lysine 14 chromatin signature underlies tissue-specific gene regulation.
  11. ArchR is a scalable software package for integrative single-cell chromatin accessibility analysis.
  12. Chromatin dysregulation associated with NSD1 mutation in head and neck squamous cell carcinoma.
  13. FOXF1 is required for the oncogenic properties of PAX3-FOXO1 in rhabdomyosarcoma.
  14. Comprehensive analysis of single cell ATAC-seq data with SnapATAC.
  15. Alternative RNA structures formed during transcription depend on elongation rate and modify RNA processing.
  16. Functional antagonism of chromatin modulators regulates epithelial-mesenchymal transition.
  17. Chromatin information content landscapes inform transcription factor and DNA interactions.
  18. Regional identity of human neural stem cells determines oncogenic responses to histone H3.3 mutants.
  19. Regulation of MYB by distal enhancer elements in human myeloid leukemia.
  1. Nat Commun. 2021 02 23. 12(1): 1247
    Single-cell multiomics sequencing reveals the functional regulatory landscape of early embryos.
    Yang Wang, Peng Yuan, Zhiqiang Yan, Ming Yang, Ying Huo, Yanli Nie, Xiaohui Zhu, Jie Qiao, Liying Yan.
      Extensive epigenetic reprogramming occurs during preimplantation embryo development. However, it remains largely unclear how the drastic epigenetic reprogramming contributes to transcriptional regulatory network during this period. Here, we develop a single-cell multiomics sequencing technology (scNOMeRe-seq) that enables profiling of genome-wide chromatin accessibility, DNA methylation and RNA expression in the same individual cell. We apply this method to depict a single-cell multiomics map of mouse preimplantation development. We find that genome-wide DNA methylation remodeling facilitates the reconstruction of genetic lineages in early embryos. Further, we construct a zygotic genome activation (ZGA)-associated regulatory network and reveal coordination among multiple epigenetic layers, transcription factors and repeat elements that instruct proper ZGA. Cell fates associated cis-regulatory elements are activated stepwise in post-ZGA stages. Trophectoderm (TE)-specific transcription factors play dual roles in promoting the TE program while repressing the inner cell mass (ICM) program during the ICM/TE separation.
    DOI:  https://doi.org/10.1038/s41467-021-21409-8
  2. Circulation. 2021 Feb 25.
    The Transcription Factor MAFF Regulates an Atherosclerosis Relevant Network Connecting Inflammation and Cholesterol Metabolism.
    Moritz von Scheidt, Yuqi Zhao, Thomas Q de Aguiar Vallim, Nam Che, Michael Wierer, Marcus M Seldin, Oscar Franzén, Zeyneb Kurt, Shichao Pang, Dario Bongiovanni, Masayuki Yamamoto, Peter A Edwards, Arno Ruusalepp, Jason C Kovacic, Matthias Mann, Johan L M Björkegren, Aldons J Lusis, Xia Yang, Heribert Schunkert.
      Background: Coronary artery disease (CAD) is a multifactorial condition with both genetic and exogenous causes. The contribution of tissue specific functional networks to the development of atherosclerosis remains largely unclear. The aim of this study was to identify and characterise central regulators and networks leading to atherosclerosis. Methods: Based on several hundred genes known to affect atherosclerosis risk in mouse (as demonstrated in knock-out models) and human (as shown by genome-wide association studies (GWAS)) liver gene regulatory networks were modeled. The hierarchical order and regulatory directions of genes within the network were based on Bayesian prediction models as well as experimental studies including chromatin immunoprecipitation DNA-Sequencing (ChIP-Seq), ChIP mass spectrometry (ChIP-MS), overexpression, siRNA knockdown in mouse and human liver cells, and knockout mouse experiments. Bioinformatics and correlation analyses were used to clarify associations between central genes and CAD phenotypes in both human and mouse. Results: The transcription factor MAFF interacted as a key driver of a liver network with three human genes at CAD GWAS loci and eleven atherosclerotic murine genes. Most importantly, expression levels of the low-density lipoprotein receptor (LDLR) gene correlated with MAFF in 600 CAD patients undergoing bypass surgery (STARNET) and a hybrid mouse diversity panel involving 105 different inbred mouse strains. Molecular mechanisms of MAFF were tested under non-inflammatory conditions showing a positive correlation between MAFF and LDLR in vitro and in vivo. Interestingly, after LPS stimulation (inflammatory conditions) an inverse correlation between MAFF and LDLR in vitro and in vivo was observed. ChIP-MS revealed that the human CAD GWAS candidate BACH1 assists MAFF in the presence of LPS stimulation with respective heterodimers binding at the MAF recognition element (MARE) of the LDLR promoter to transcriptionally downregulate LDLR expression. Conclusions: The transcription factor MAFF was identified as a novel central regulator of an atherosclerosis/CAD relevant liver network. MAFF triggered context specific expression of LDLR and other genes known to affect CAD risk. Our results suggest that MAFF is a missing link between inflammation, lipid and lipoprotein metabolism and a possible treatment target.
    Keywords:  BACH1; LDLR; MAFF; key driver analysis; network modeling
    DOI:  https://doi.org/10.1161/CIRCULATIONAHA.120.050186
  3. Nucleic Acids Res. 2021 Feb 23. pii: gkab107. [Epub ahead of print]
    Role of CxxC-finger protein 1 in establishing mouse oocyte epigenetic landscapes.
    Qian-Qian Sha, Ye-Zhang Zhu, Yunlong Xiang, Jia-Li Yu, Xiao-Ying Fan, Yan-Chu Li, Yun-Wen Wu, Li Shen, Heng-Yu Fan.
      During oogenesis, oocytes gain competence and subsequently undergo meiotic maturation and prepare for embryonic development; trimethylated histone H3 on lysine-4 (H3K4me3) mediates a wide range of nuclear events during these processes. Oocyte-specific knockout of CxxC-finger protein 1 (CXXC1, also known as CFP1) impairs H3K4me3 accumulation and causes changes in chromatin configurations. This study investigated the changes in genomic H3K4me3 landscapes in oocytes with Cxxc1 knockout and the effects on other epigenetic factors such as the DNA methylation, H3K27me3, H2AK119ub1 and H3K36me3. H3K4me3 is overall decreased after knocking out Cxxc1, including both the promoter region and the gene body. CXXC1 and MLL2, which is another histone H3 methyltransferase, have nonoverlapping roles in mediating H3K4 trimethylation during oogenesis. Cxxc1 deletion caused a decrease in DNA methylation levels and affected H3K27me3 and H2AK119ub1 distributions, particularly at regions with high DNA methylation levels. The changes in epigenetic networks implicated by Cxxc1 deletion were correlated with the transcriptional changes in genes in the corresponding genomic regions. This study elucidates the epigenetic changes underlying the phenotypes and molecular defects in oocytes with deleted Cxxc1 and highlights the role of CXXC1 in orchestrating multiple factors that are involved in establishing the appropriate epigenetic states of maternal genome.
    DOI:  https://doi.org/10.1093/nar/gkab107
  4. Dev Cell. 2021 Feb 24. pii: S1534-5807(21)00116-7. [Epub ahead of print]
    FoxA-dependent demethylation of DNA initiates epigenetic memory of cellular identity.
    Yitzhak Reizel, Ashleigh Morgan, Long Gao, Jonathan Schug, Sarmistha Mukherjee, Meilín Fernández García, Greg Donahue, Joseph A Baur, Kenneth S Zaret, Klaus H Kaestner.
      Tissue-specific DNA methylation patterns are created by transcription factors that recruit methylation and demethylation enzymes to cis-regulatory elements. To date, it is not known whether transcription factors are needed to continuously maintain methylation profiles in development and mature tissues or whether they only establish these marks during organ development. We queried the role of the pioneer factor FoxA in generating hypomethylated DNA at liver enhancers. We discovered a set of FoxA-binding sites that undergo regional, FoxA-dependent demethylation during organ development. Conditional ablation of FoxA genes in the adult liver demonstrated that continued FoxA presence was not required to maintain the hypomethylated state, even when massive cell proliferation was induced. This study provides strong evidence for the stable, epigenetic nature of tissue-specific DNA methylation patterns directed by lineage-determining transcription factors during organ development.
    Keywords:  DNA methylation; FoxA; enhancer activity; liver; tissue differentiation
    DOI:  https://doi.org/10.1016/j.devcel.2021.02.005
  5. Proc Natl Acad Sci U S A. 2021 Mar 02. pii: e2021795118. [Epub ahead of print]118(9):
    Depletion of H3K36me2 recapitulates epigenomic and phenotypic changes induced by the H3.3K36M oncohistone mutation.
    Kartik N Rajagopalan, Xiao Chen, Daniel N Weinberg, Haifen Chen, Jacek Majewski, C David Allis, Chao Lu.
      Hotspot histone H3 mutations have emerged as drivers of oncogenesis in cancers of multiple lineages. Specifically, H3 lysine 36 to methionine (H3K36M) mutations are recurrently identified in chondroblastomas, undifferentiated sarcomas, and head and neck cancers. While the mutation reduces global levels of both H3K36 dimethylation (H3K36me2) and trimethylation (H3K36me3) by dominantly inhibiting their respective specific methyltransferases, the relative contribution of these methylation states to the chromatin and phenotypic changes associated with H3K36M remains unclear. Here, we specifically deplete H3K36me2 or H3K36me3 in mesenchymal cells, using CRISPR-Cas9 to separately knock out the corresponding methyltransferases NSD1/2 or SETD2. By profiling and comparing the epigenomic and transcriptomic landscapes of these cells with cells expressing the H3.3K36M oncohistone, we find that the loss of H3K36me2 could largely recapitulate H3.3K36M's effect on redistribution of H3K27 trimethylation (H3K27me3) and gene expression. Consistently, knockout of Nsd1/2, but not Setd2, phenocopies the differentiation blockade and hypersensitivity to the DNA-hypomethylating agent induced by H3K36M. Together, our results support a functional divergence between H3K36me2 and H3K36me3 and their nonredundant roles in H3K36M-driven oncogenesis.
    Keywords:  H3K36 methylation; NSD; cancer; chromatin and epigenomics; oncohistone
    DOI:  https://doi.org/10.1073/pnas.2021795118
  6. Commun Biol. 2021 Feb 22. 4(1): 239
    Annotation of chromatin states in 66 complete mouse epigenomes during development.
    Arjan van der Velde, Kaili Fan, Junko Tsuji, Jill E Moore, Michael J Purcaro, Henry E Pratt, Zhiping Weng.
      The morphologically and functionally distinct cell types of a multicellular organism are maintained by their unique epigenomes and gene expression programs. Phase III of the ENCODE Project profiled 66 mouse epigenomes across twelve tissues at daily intervals from embryonic day 11.5 to birth. Applying the ChromHMM algorithm to these epigenomes, we annotated eighteen chromatin states with characteristics of promoters, enhancers, transcribed regions, repressed regions, and quiescent regions. Our integrative analyses delineate the tissue specificity and developmental trajectory of the loci in these chromatin states. Approximately 0.3% of each epigenome is assigned to a bivalent chromatin state, which harbors both active marks and the repressive mark H3K27me3. Highly evolutionarily conserved, these loci are enriched in silencers bound by polycomb repressive complex proteins, and the transcription start sites of their silenced target genes. This collection of chromatin state assignments provides a useful resource for studying mammalian development.
    DOI:  https://doi.org/10.1038/s42003-021-01756-4
  7. Curr Genet. 2021 Feb 26.
    Forkhead transcription factor Fkh1: insights into functional regulatory domains crucial for recruitment of Sin3 histone deacetylase complex.
    Rasha Aref, Marwa N M E Sanad, Hans-Joachim Schüller.
      Transcription factors are inextricably linked with histone deacetylases leading to compact chromatin. The Forkhead transcription factor Fkh1 is mainly a negative transcriptional regulator which affects cell cycle control, silencing of mating-type cassettes and induction of pseudohyphal growth in the yeast Saccharomyces cerevisiae. Markedly, Fkh1 impinges chromatin architecture by recruiting large regulatory complexes. Implication of Fkh1 with transcriptional corepressor complexes remains largely unexplored. In this work we show that Fkh1 directly recruits corepressors Sin3 and Tup1 (but not Cyc8), providing evidence for its influence on epigenetic regulation. We also identified the specific domain of Fkh1 mediating Sin3 recruitment and substantiated that amino acids 51-125 of Fkh1 bind PAH2 of Sin3. Importantly, this part of Fkh1 overlaps with its Forkhead-associated domain (FHA). To analyse this domain in more detail, selected amino acids were replaced by alanine, revealing that hydrophobic amino acids L74 and I78 are important for Fkh1-Sin3 binding. In addition, we could prove Fkh1 recruitment to promoters of cell cycle genes CLB2 and SWI5. Notably, Sin3 is also recruited to these promoters but only in the presence of functional Fkh1. Our results disclose that recruitment of Sin3 to Fkh1 requires precisely positioned Fkh1/Sin3 binding sites which provide an extended view on the genetic control of cell cycle genes CLB2 and SWI5 and the mechanism of transcriptional repression by modulation of chromatin architecture at the G2/M transition.
    Keywords:  Cell cycle genes; Fkh1; Histone deacetylases (HDACs); Sin3; Tup1
    DOI:  https://doi.org/10.1007/s00294-021-01158-3
  8. Cell Rep. 2021 Feb 23. pii: S2211-1247(21)00096-6. [Epub ahead of print]34(8): 108783
    Distinct properties and functions of CTCF revealed by a rapidly inducible degron system.
    Jing Luan, Guanjue Xiang, Pablo Aurelio Gómez-García, Jacob M Tome, Zhe Zhang, Marit W Vermunt, Haoyue Zhang, Anran Huang, Cheryl A Keller, Belinda M Giardine, Yu Zhang, Yemin Lan, John T Lis, Melike Lakadamyali, Ross C Hardison, Gerd A Blobel.
      CCCTC-binding factor (CTCF) is a conserved zinc finger transcription factor implicated in a wide range of functions, including genome organization, transcription activation, and elongation. To explore the basis for CTCF functional diversity, we coupled an auxin-induced degron system with precision nuclear run-on. Unexpectedly, oriented CTCF motifs in gene bodies are associated with transcriptional stalling in a manner independent of bound CTCF. Moreover, CTCF at different binding sites (CBSs) displays highly variable resistance to degradation. Motif sequence does not significantly predict degradation behavior, but location at chromatin boundaries and chromatin loop anchors, as well as co-occupancy with cohesin, are associated with delayed degradation. Single-molecule tracking experiments link chromatin residence time to CTCF degradation kinetics, which has ramifications regarding architectural CTCF functions. Our study highlights the heterogeneity of CBSs, uncovers properties specific to architecturally important CBSs, and provides insights into the basic processes of genome organization and transcription regulation.
    Keywords:  CTCF; PRO-seq; chromatin architecture; cohesin; degradation dynamics; residence time; single-molecule tracking; transcription elongation stalling
    DOI:  https://doi.org/10.1016/j.celrep.2021.108783
  9. Genome Res. 2021 Feb 24. pii: gr.269068.120. [Epub ahead of print]
    Iterative epigenomic analyses in the same single cell.
    Hidetaka Ohnuki, David J Venzon, Alexei Lobanov, Giovanna Tosato.
      Gene expression in individual cells is epigenetically regulated by DNA modifications, histone modifications, transcription factors and other DNA-binding proteins. It has been shown that multiple histone modifications can predict gene expression and reflect future responses of bulk cells to extracellular cues. However, the predictive ability of epigenomic analysis is still limited for mechanistic research at a single cell level. To overcome this limitation, it would be useful to acquire reliable signals from multiple epigenetic marks in the same single cell. Here, we propose a new approach and a new method for analysis of several components of the epigenome in the same single cell. The new method allows reanalysis of the same single cell. We found that reanalysis of the same single cell is feasible, provides confirmation of the epigenetic signals and allows application of statistical analysis to identify reproduced reads using datasets generated only from the single cell. Reanalysis of the same single cell is also useful to acquire multiple-epigenetic marks from the same single cells. The method can acquire at least 5 epigenetic marks, H3K27ac, H3K27me3, mediator complex subunit 1, a DNA modification and a DNA interacting protein. We could predict active signaling pathways in K562 single cells using the epigenetic data and confirm that the predicted results strongly correlate with actual active signaling pathways identified by RNA-seq results. These results suggest that the new method provides mechanistic insights for cellular phenotypes through multi-layered epigenome analysis in the same single cells.
    DOI:  https://doi.org/10.1101/gr.269068.120
  10. Mol Cell. 2021 Feb 17. pii: S1097-2765(21)00061-7. [Epub ahead of print]
    A unique histone 3 lysine 14 chromatin signature underlies tissue-specific gene regulation.
    Isabel Regadas, Olle Dahlberg, Roshan Vaid, Oanh Ho, Sergey Belikov, Gunjan Dixit, Sebastian Deindl, Jiayu Wen, Mattias Mannervik.
      Organismal development and cell differentiation critically depend on chromatin state transitions. However, certain developmentally regulated genes lack histone 3 lysine 9 and 27 acetylation (H3K9ac and H3K27ac, respectively) and histone 3 lysine 4 (H3K4) methylation, histone modifications common to most active genes. Here we describe a chromatin state featuring unique histone 3 lysine 14 acetylation (H3K14ac) peaks in key tissue-specific genes in Drosophila and human cells. Replacing H3K14 in Drosophila demonstrates that H3K14 is essential for expression of genes devoid of canonical histone modifications in the embryonic gut and larval wing imaginal disc, causing lethality and defective wing patterning. We find that the SWI/SNF protein Brahma (Brm) recognizes H3K14ac, that brm acts in the same genetic pathway as H3K14R, and that chromatin accessibility at H3K14ac-unique genes is decreased in H3K14R mutants. Our results show that acetylation of a single lysine is essential at genes devoid of canonical histone marks and uncover an important requirement for H3K14 in tissue-specific gene regulation.
    Keywords:  Brahma; Drosophila; SWI/SNF; chromatin state; developmental genomics; gene regulation; histone acetylation; mesenchymal stem cells
    DOI:  https://doi.org/10.1016/j.molcel.2021.01.041
  11. Nat Genet. 2021 Feb 25.
    ArchR is a scalable software package for integrative single-cell chromatin accessibility analysis.
    Jeffrey M Granja, M Ryan Corces, Sarah E Pierce, S Tansu Bagdatli, Hani Choudhry, Howard Y Chang, William J Greenleaf.
      The advent of single-cell chromatin accessibility profiling has accelerated the ability to map gene regulatory landscapes but has outpaced the development of scalable software to rapidly extract biological meaning from these data. Here we present a software suite for single-cell analysis of regulatory chromatin in R (ArchR; https://www.archrproject.com/ ) that enables fast and comprehensive analysis of single-cell chromatin accessibility data. ArchR provides an intuitive, user-focused interface for complex single-cell analyses, including doublet removal, single-cell clustering and cell type identification, unified peak set generation, cellular trajectory identification, DNA element-to-gene linkage, transcription factor footprinting, mRNA expression level prediction from chromatin accessibility and multi-omic integration with single-cell RNA sequencing (scRNA-seq). Enabling the analysis of over 1.2 million single cells within 8 h on a standard Unix laptop, ArchR is a comprehensive software suite for end-to-end analysis of single-cell chromatin accessibility that will accelerate the understanding of gene regulation at the resolution of individual cells.
    DOI:  https://doi.org/10.1038/s41588-021-00790-6
  12. Cell Rep. 2021 Feb 23. pii: S2211-1247(21)00082-6. [Epub ahead of print]34(8): 108769
    Chromatin dysregulation associated with NSD1 mutation in head and neck squamous cell carcinoma.
    Nargess Farhangdoost, Cynthia Horth, Bo Hu, Eric Bareke, Xiao Chen, Yinglu Li, Mariel Coradin, Benjamin A Garcia, Chao Lu, Jacek Majewski.
      Chromatin dysregulation has emerged as an important mechanism of oncogenesis. To develop targeted treatments, it is important to understand the transcriptomic consequences of mutations in chromatin modifier genes. Recently, mutations in the histone methyltransferase gene nuclear receptor binding SET domain protein 1 (NSD1) have been identified in a subset of common and deadly head and neck squamous cell carcinomas (HNSCCs). Here, we use genome-wide approaches and genome editing to dissect the downstream effects of loss of NSD1 in HNSCC. We demonstrate that NSD1 mutations are responsible for loss of intergenic H3K36me2 domains, followed by loss of DNA methylation and gain of H3K27me3 in the affected genomic regions. In addition, those regions are enriched in cis-regulatory elements, and subsequent loss of H3K27ac correlates with reduced expression of their target genes. Our analysis identifies genes and pathways affected by the loss of NSD1 and paves the way to further understanding the interplay among chromatin modifications in cancer.
    Keywords:  cis-regulatory elements; epigenomics; head and neck squamous cell carcinoma; histone H3 lysine 36 dimethylation; histone modifications; nuclear receptor binding SET domain protein 1
    DOI:  https://doi.org/10.1016/j.celrep.2021.108769
  13. Oncogene. 2021 Feb 24.
    FOXF1 is required for the oncogenic properties of PAX3-FOXO1 in rhabdomyosarcoma.
    David Milewski, Samriddhi Shukla, Berkley E Gryder, Arun Pradhan, Johnny Donovan, Parvathi Sudha, Sushmitha Vallabh, Athena Pyros, Yan Xu, Artem Barski, Sara Szabo, Brian Turpin, Joseph G Pressey, Douglas P Millay, Javed Khan, Vladimir V Kalinichenko, Tanya V Kalin.
      The PAX3-FOXO1 fusion protein is the key oncogenic driver in fusion positive rhabdomyosarcoma (FP-RMS), an aggressive soft tissue malignancy with a particularly poor prognosis. Identifying key downstream targets of PAX3-FOXO1 will provide new therapeutic opportunities for treatment of FP-RMS. Herein, we demonstrate that Forkhead Box F1 (FOXF1) transcription factor is uniquely expressed in FP-RMS and is required for FP-RMS tumorigenesis. The PAX3-FOXO1 directly binds to FOXF1 enhancers and induces FOXF1 gene expression. CRISPR/Cas9 mediated inactivation of either FOXF1 coding sequence or FOXF1 enhancers suppresses FP-RMS tumorigenesis even in the presence of PAX3-FOXO1 oncogene. Knockdown or genetic knockout of FOXF1 induces myogenic differentiation in PAX3-FOXO1-positive FP-RMS. Over-expression of FOXF1 decreases myogenic differentiation in primary human myoblasts. In FP-RMS tumor cells, FOXF1 protein binds chromatin near enhancers associated with FP-RMS gene signature. FOXF1 cooperates with PAX3-FOXO1 and E-box transcription factors MYOD1 and MYOG to regulate FP-RMS-specific gene expression. Altogether, FOXF1 functions downstream of PAX3-FOXO1 to promote FP-RMS tumorigenesis.
    DOI:  https://doi.org/10.1038/s41388-021-01694-9
  14. Nat Commun. 2021 Feb 26. 12(1): 1337
    Comprehensive analysis of single cell ATAC-seq data with SnapATAC.
    Rongxin Fang, Sebastian Preissl, Yang Li, Xiaomeng Hou, Jacinta Lucero, Xinxin Wang, Amir Motamedi, Andrew K Shiau, Xinzhu Zhou, Fangming Xie, Eran A Mukamel, Kai Zhang, Yanxiao Zhang, M Margarita Behrens, Joseph R Ecker, Bing Ren.
      Identification of the cis-regulatory elements controlling cell-type specific gene expression patterns is essential for understanding the origin of cellular diversity. Conventional assays to map regulatory elements via open chromatin analysis of primary tissues is hindered by sample heterogeneity. Single cell analysis of accessible chromatin (scATAC-seq) can overcome this limitation. However, the high-level noise of each single cell profile and the large volume of data pose unique computational challenges. Here, we introduce SnapATAC, a software package for analyzing scATAC-seq datasets. SnapATAC dissects cellular heterogeneity in an unbiased manner and map the trajectories of cellular states. Using the Nyström method, SnapATAC can process data from up to a million cells. Furthermore, SnapATAC incorporates existing tools into a comprehensive package for analyzing single cell ATAC-seq dataset. As demonstration of its utility, SnapATAC is applied to 55,592 single-nucleus ATAC-seq profiles from the mouse secondary motor cortex. The analysis reveals ~370,000 candidate regulatory elements in 31 distinct cell populations in this brain region and inferred candidate cell-type specific transcriptional regulators.
    DOI:  https://doi.org/10.1038/s41467-021-21583-9
  15. Mol Cell. 2021 Feb 17. pii: S1097-2765(21)00060-5. [Epub ahead of print]
    Alternative RNA structures formed during transcription depend on elongation rate and modify RNA processing.
    Tassa Saldi, Kent Riemondy, Benjamin Erickson, David L Bentley.
      Most RNA processing occurs co-transcriptionally. We interrogated nascent pol II transcripts by chemical and enzymatic probing and determined how the "nascent RNA structureome" relates to splicing, A-I editing and transcription speed. RNA folding within introns and steep structural transitions at splice sites are associated with efficient co-transcriptional splicing. A slow pol II mutant elicits extensive remodeling into more folded conformations with increased A-I editing. Introns that become more structured at their 3' splice sites get co-transcriptionally excised more efficiently. Slow pol II altered folding of intronic Alu elements where cryptic splicing and intron retention are stimulated, an outcome mimicked by UV, which decelerates transcription. Slow transcription also remodeled RNA folding around alternative exons in distinct ways that predict whether skipping or inclusion is favored, even though it occurs post-transcriptionally. Hence, co-transcriptional RNA folding modulates post-transcriptional alternative splicing. In summary, the plasticity of nascent transcripts has widespread effects on RNA processing.
    Keywords:  RNA editing; alternative splicing; co-transcriptional splicing; nascent RNA structureome; pol II transcription elongation; splice site structure
    DOI:  https://doi.org/10.1016/j.molcel.2021.01.040
  16. Sci Adv. 2021 Feb;pii: eabd7974. [Epub ahead of print]7(9):
    Functional antagonism of chromatin modulators regulates epithelial-mesenchymal transition.
    Michela Serresi, Sonia Kertalli, Lifei Li, Matthias Jürgen Schmitt, Yuliia Dramaretska, Jikke Wierikx, Danielle Hulsman, Gaetano Gargiulo.
      Epithelial-mesenchymal transition (EMT) is a developmental process hijacked by cancer cells to modulate proliferation, migration, and stress response. Whereas kinase signaling is believed to be an EMT driver, the molecular mechanisms underlying epithelial-mesenchymal interconversion are incompletely understood. Here, we show that the impact of chromatin regulators on EMT interconversion is broader than that of kinases. By combining pharmacological modulation of EMT, synthetic genetic tracing, and CRISPR interference screens, we uncovered a minority of kinases and several chromatin remodelers, writers, and readers governing homeostatic EMT in lung cancer cells. Loss of ARID1A, DOT1L, BRD2, and ZMYND8 had nondeterministic and sometimes opposite consequences on epithelial-mesenchymal interconversion. Together with RNAPII and AP-1, these antagonistic gatekeepers control chromatin of active enhancers, including pan-cancer-EMT signature genes enabling supraclassification of anatomically diverse tumors. Thus, our data uncover general principles underlying transcriptional control of cancer cell plasticity and offer a platform to systematically explore chromatin regulators in tumor-state-specific therapy.
    DOI:  https://doi.org/10.1126/sciadv.abd7974
  17. Nat Commun. 2021 Feb 26. 12(1): 1307
    Chromatin information content landscapes inform transcription factor and DNA interactions.
    Ricardo D'Oliveira Albanus, Yasuhiro Kyono, John Hensley, Arushi Varshney, Peter Orchard, Jacob O Kitzman, Stephen C J Parker.
      Interactions between transcription factors and chromatin are fundamental to genome organization and regulation and, ultimately, cell state. Here, we use information theory to measure signatures of organized chromatin resulting from transcription factor-chromatin interactions encoded in the patterns of the accessible genome, which we term chromatin information enrichment (CIE). We calculate CIE for hundreds of transcription factor motifs across human samples and identify two classes: low and high CIE. The 10-20% of common and tissue-specific high CIE transcription factor motifs, associate with higher protein-DNA residence time, including different binding site subclasses of the same transcription factor, increased nucleosome phasing, specific protein domains, and the genetic control of both chromatin accessibility and gene expression. These results show that variations in the information encoded in chromatin architecture reflect functional biological variation, with implications for cell state dynamics and memory.
    DOI:  https://doi.org/10.1038/s41467-021-21534-4
  18. Cell Stem Cell. 2021 Feb 19. pii: S1934-5909(21)00016-3. [Epub ahead of print]
    Regional identity of human neural stem cells determines oncogenic responses to histone H3.3 mutants.
    Raul Bardini Bressan, Benjamin Southgate, Kirsty M Ferguson, Carla Blin, Vivien Grant, Neza Alfazema, Jimi C Wills, Maria Angeles Marques-Torrejon, Gillian M Morrison, James Ashmore, Faye Robertson, Charles A C Williams, Leanne Bradley, Alex von Kriegsheim, Richard A Anderson, Simon R Tomlinson, Steven M Pollard.
      Point mutations within the histone H3.3 are frequent in aggressive childhood brain tumors known as pediatric high-grade gliomas (pHGGs). Intriguingly, distinct mutations arise in discrete anatomical regions: H3.3-G34R within the forebrain and H3.3-K27M preferentially within the hindbrain. The reasons for this contrasting etiology are unknown. By engineering human fetal neural stem cell cultures from distinct brain regions, we demonstrate here that cell-intrinsic regional identity provides differential responsiveness to each mutant that mirrors the origins of pHGGs. Focusing on H3.3-G34R, we find that the oncohistone supports proliferation of forebrain cells while inducing a cytostatic response in the hindbrain. Mechanistically, H3.3-G34R does not impose widespread transcriptional or epigenetic changes but instead impairs recruitment of ZMYND11, a transcriptional repressor of highly expressed genes. We therefore propose that H3.3-G34R promotes tumorigenesis by focally stabilizing the expression of key progenitor genes, thereby locking initiating forebrain cells into their pre-existing immature state.
    Keywords:  DIPG; ZMYND11; cancer; forebrain; glioblastoma; histone H3.3; neural stem cells; neurodevelopment; pediatric high-grade glioma
    DOI:  https://doi.org/10.1016/j.stem.2021.01.016
  19. Cell Death Dis. 2021 Feb 26. 12(2): 223
    Regulation of MYB by distal enhancer elements in human myeloid leukemia.
    Mengjia Li, Penglei Jiang, Kai Cheng, Zehui Zhang, Shuyu Lan, Xiaoxia Li, Lirong Zhao, Yucheng Wang, Xiang Wang, Jing Chen, Tao Ji, Bingshe Han, Junfang Zhang.
      MYB plays vital roles in regulating proliferation and differentiation of hematopoietic progenitor cells, dysregulation of MYB has been implicated in the pathogenesis of leukemia. Although the transcription of MYB has been well studied, its detailed underlying regulatory mechanisms still remain elusive. Here, we detected the long-range interaction between the upstream regions, -34k and -88k, and the MYB promoter in K562, U937, and HL-60 cells using circularized chromosome conformation capture (4C) assay, which declined when MYB was downregulated during chemical-induced differentiation. The enrichment of enhancer markers, H3K4me1 and H3K27ac, and enhancer activity at the -34k and -88k regions were confirmed by ChIP-qPCR and luciferase assay respectively. ChIP-qPCR showed the dynamic binding of GATA1, TAL1, and CCAAT/enhancer-binding protein (C/EBPβ) at -34k and -88k during differentiation of K562 cells. Epigenome editing by a CRISPR-Cas9-based method showed that H3K27ac at -34k enhanced TF binding and MYB expression, while DNA methylation inhibited MYB expression. Taken together, our data revealed that enhancer elements at -34k are required for MYB expression, TF binding, and epigenetic modification are closely involved in this process in human myeloid leukemia cells.
    DOI:  https://doi.org/10.1038/s41419-021-03515-z
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