Publications by authors named "Arthur I Skoultchi"

56 Publications

H1 histones control the epigenetic landscape by local chromatin compaction.

Nature 2021 01 9;589(7841):293-298. Epub 2020 Dec 9.

Department of Cell Biology, Albert Einstein College of Medicine, New York, NY, USA.

H1 linker histones are the most abundant chromatin-binding proteins. In vitro studies indicate that their association with chromatin determines nucleosome spacing and enables arrays of nucleosomes to fold into more compact chromatin structures. However, the in vivo roles of H1 are poorly understood. Here we show that the local density of H1 controls the balance of repressive and active chromatin domains by promoting genomic compaction. We generated a conditional triple-H1-knockout mouse strain and depleted H1 in haematopoietic cells. H1 depletion in T cells leads to de-repression of T cell activation genes, a process that mimics normal T cell activation. Comparison of chromatin structure in normal and H1-depleted CD8 T cells reveals that H1-mediated chromatin compaction occurs primarily in regions of the genome containing higher than average levels of H1: the chromosome conformation capture (Hi-C) B compartment and regions of the Hi-C A compartment marked by PRC2. Reduction of H1 stoichiometry leads to decreased H3K27 methylation, increased H3K36 methylation, B-to-A-compartment shifting and an increase in interaction frequency between compartments. In vitro, H1 promotes PRC2-mediated H3K27 methylation and inhibits NSD2-mediated H3K36 methylation. Mechanistically, H1 mediates these opposite effects by promoting physical compaction of the chromatin substrate. Our results establish H1 as a critical regulator of gene silencing through localized control of chromatin compaction, 3D genome organization and the epigenetic landscape.
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http://dx.doi.org/10.1038/s41586-020-3032-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8110206PMC
January 2021

Histone H1 loss drives lymphoma by disrupting 3D chromatin architecture.

Nature 2021 01 9;589(7841):299-305. Epub 2020 Dec 9.

Division of Hematology and Medical Oncology, Sanford I. Weill Department of Medicine, Weill Cornell Medicine, New York, NY, USA.

Linker histone H1 proteins bind to nucleosomes and facilitate chromatin compaction, although their biological functions are poorly understood. Mutations in the genes that encode H1 isoforms B-E (H1B, H1C, H1D and H1E; also known as H1-5, H1-2, H1-3 and H1-4, respectively) are highly recurrent in B cell lymphomas, but the pathogenic relevance of these mutations to cancer and the mechanisms that are involved are unknown. Here we show that lymphoma-associated H1 alleles are genetic driver mutations in lymphomas. Disruption of H1 function results in a profound architectural remodelling of the genome, which is characterized by large-scale yet focal shifts of chromatin from a compacted to a relaxed state. This decompaction drives distinct changes in epigenetic states, primarily owing to a gain of histone H3 dimethylation at lysine 36 (H3K36me2) and/or loss of repressive H3 trimethylation at lysine 27 (H3K27me3). These changes unlock the expression of stem cell genes that are normally silenced during early development. In mice, loss of H1c and H1e (also known as H1f2 and H1f4, respectively) conferred germinal centre B cells with enhanced fitness and self-renewal properties, ultimately leading to aggressive lymphomas with an increased repopulating potential. Collectively, our data indicate that H1 proteins are normally required to sequester early developmental genes into architecturally inaccessible genomic compartments. We also establish H1 as a bona fide tumour suppressor and show that mutations in H1 drive malignant transformation primarily through three-dimensional genome reorganization, which leads to epigenetic reprogramming and derepression of developmentally silenced genes.
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http://dx.doi.org/10.1038/s41586-020-3017-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7855728PMC
January 2021

Single-molecule imaging of transcription dynamics in somatic stem cells.

Nature 2020 07 24;583(7816):431-436. Epub 2020 Jun 24.

Department of Cell Biology, Albert Einstein College of Medicine, New York, NY, USA.

Molecular noise is a natural phenomenon that is inherent to all biological systems. How stochastic processes give rise to the robust outcomes that support tissue homeostasis remains unclear. Here we use single-molecule RNA fluorescent in situ hybridization (smFISH) on mouse stem cells derived from haematopoietic tissue to measure the transcription dynamics of three key genes that encode transcription factors: PU.1 (also known as Spi1), Gata1 and Gata2. We find that infrequent, stochastic bursts of transcription result in the co-expression of these antagonistic transcription factors in the majority of haematopoietic stem and progenitor cells. Moreover, by pairing smFISH with time-lapse microscopy and the analysis of pedigrees, we find that although individual stem-cell clones produce descendants that are in transcriptionally related states-akin to a transcriptional priming phenomenon-the underlying transition dynamics between states are best captured by stochastic and reversible models. As such, a stochastic process can produce cellular behaviours that may be incorrectly inferred to have arisen from deterministic dynamics. We propose a model whereby the intrinsic stochasticity of gene expression facilitates, rather than impedes, the concomitant maintenance of transcriptional plasticity and stem cell robustness.
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http://dx.doi.org/10.1038/s41586-020-2432-4DOI Listing
July 2020

H1 linker histones silence repetitive elements by promoting both histone H3K9 methylation and chromatin compaction.

Proc Natl Acad Sci U S A 2020 06 8;117(25):14251-14258. Epub 2020 Jun 8.

Department of Cell Biology, Albert Einstein College of Medicine, Bronx, NY 10461;

Nearly 50% of mouse and human genomes are composed of repetitive sequences. Transcription of these sequences is tightly controlled during development to prevent genomic instability, inappropriate gene activation and other maladaptive processes. Here, we demonstrate an integral role for H1 linker histones in silencing repetitive elements in mouse embryonic stem cells. Strong H1 depletion causes a profound de-repression of several classes of repetitive sequences, including major satellite, LINE-1, and ERV. Activation of repetitive sequence transcription is accompanied by decreased H3K9 trimethylation of repetitive sequence chromatin. H1 linker histones interact directly with Suv39h1, Suv39h2, and SETDB1, the histone methyltransferases responsible for H3K9 trimethylation of chromatin within these regions, and stimulate their activity toward chromatin in vitro. However, we also implicate chromatin compaction mediated by H1 as an additional, dominant repressive mechanism for silencing of repetitive major satellite sequences. Our findings elucidate two distinct, H1-mediated pathways for silencing heterochromatin.
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http://dx.doi.org/10.1073/pnas.1920725117DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7322038PMC
June 2020

Linker histone H1.2 and H1.4 affect the neutrophil lineage determination.

Elife 2020 05 11;9. Epub 2020 May 11.

Max Planck Institute for Infection Biology, Department of Cellular Microbiology, Berlin, Germany.

Neutrophils are important innate immune cells that tackle invading pathogens with different effector mechanisms. They acquire this antimicrobial potential during their maturation in the bone marrow, where they differentiate from hematopoietic stem cells in a process called granulopoiesis. Mature neutrophils are terminally differentiated and short-lived with a high turnover rate. Here, we show a critical role for linker histone H1 on the differentiation and function of neutrophils using a genome-wide CRISPR/Cas9 screen in the human cell line PLB-985. We systematically disrupted expression of somatic H1 subtypes to show that individual H1 subtypes affect PLB-985 maturation in opposite ways. Loss of H1.2 and H1.4 induced an eosinophil-like transcriptional program, thereby negatively regulating the differentiation into the neutrophil lineage. Importantly, H1 subtypes also affect neutrophil differentiation and the eosinophil-directed bias of murine bone marrow stem cells, demonstrating an unexpected subtype-specific role for H1 in granulopoiesis.
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http://dx.doi.org/10.7554/eLife.52563DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7250579PMC
May 2020

The chromatin remodeler Snf2h is essential for oocyte meiotic cell cycle progression.

Genes Dev 2020 02 9;34(3-4):166-178. Epub 2020 Jan 9.

Howard Hughes Medical Institute, Boston Children's Hospital, Boston, Massachusetts 02115, USA.

Oocytes are indispensable for mammalian life. Thus, it is important to understand how mature oocytes are generated. As a critical stage of oocytes development, meiosis has been extensively studied, yet how chromatin remodeling contributes to this process is largely unknown. Here, we demonstrate that the ATP-dependent chromatin remodeling factor Snf2h (also known as Smarca5) plays a critical role in regulating meiotic cell cycle progression. Females with oocyte-specific depletion of are infertile and oocytes lacking fail to undergo meiotic resumption. Mechanistically, depletion of results in dysregulation of meiosis-related genes, which causes failure of maturation-promoting factor (MPF) activation. ATAC-seq analysis in oocytes revealed that Snf2h regulates transcription of key meiotic genes, such as , by increasing its promoter chromatin accessibility. Thus, our studies not only demonstrate the importance of Snf2h in oocyte meiotic resumption, but also reveal the mechanism underlying how a chromatin remodeling factor can regulate oocyte meiosis.
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http://dx.doi.org/10.1101/gad.331157.119DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7000916PMC
February 2020

Runx1 promotes murine erythroid progenitor proliferation and inhibits differentiation by preventing Pu.1 downregulation.

Proc Natl Acad Sci U S A 2019 09 20;116(36):17841-17847. Epub 2019 Aug 20.

Department of Cell Biology, Albert Einstein College of Medicine, Bronx, NY 10461;

Pu.1 is an ETS family transcription factor (TF) that plays critical roles in erythroid progenitors by promoting proliferation and blocking terminal differentiation. However, the mechanisms controlling expression and down-regulation of Pu.1 during early erythropoiesis have not been defined. In this study, we identify the actions of Runx1 and Pu.1 itself at the Pu.1 gene Upstream Regulatory Element (URE) as major regulators of Pu.1 expression in Burst-Forming Unit erythrocytes (BFUe). During early erythropoiesis, Runx1 and Pu.1 levels decline, and chromatin accessibility at the URE is lost. Ectopic expression of Runx1 or Pu.1, both of which bind the URE, prevents Pu.1 down-regulation and blocks terminal erythroid differentiation, resulting in extensive ex vivo proliferation and immortalization of erythroid progenitors. Ectopic expression of Runx1 in BFUe lacking a URE fails to block terminal erythroid differentiation. Thus, Runx1, acting at the URE, and Pu.1 itself directly regulate Pu.1 levels in erythroid cells, and loss of both factors is critical for Pu.1 down-regulation during terminal differentiation. The molecular mechanism of URE inactivation in erythroid cells through loss of TF binding represents a distinct pattern of Pu.1 regulation from those described in other hematopoietic cell types such as T cells which down-regulate Pu.1 through active repression. The importance of down-regulation of Runx1 and Pu.1 in erythropoiesis is further supported by genome-wide analyses showing that their DNA-binding motifs are highly overrepresented in regions that lose chromatin accessibility during early erythroid development.
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http://dx.doi.org/10.1073/pnas.1901122116DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6731665PMC
September 2019

ISWI ATPase Smarca5 Regulates Differentiation of Thymocytes Undergoing β-Selection.

J Immunol 2019 06 8;202(12):3434-3446. Epub 2019 May 8.

BIOCEV, First Faculty of Medicine, Charles University, Vestec 25250, Czech Republic;

Development of lymphoid progenitors requires a coordinated regulation of gene expression, DNA replication, and gene rearrangement. Chromatin-remodeling activities directed by SWI/SNF2 superfamily complexes play important roles in these processes. In this study, we used a conditional knockout mouse model to investigate the role of Smarca5, a member of the ISWI subfamily of such complexes, in early lymphocyte development. deficiency results in a developmental block at the DN3 stage of αβ thymocytes and pro-B stage of early B cells at which the rearrangement of Ag receptor loci occurs. It also disturbs the development of committed (CD73) γδ thymocytes. The αβ thymocyte block is accompanied by massive apoptotic depletion of β-selected double-negative DN3 cells and premitotic arrest of CD4/CD8 double-positive cells. Although -deficient αβ T cell precursors that survived apoptosis were able to undergo a successful TCRβ rearrangement, they exhibited a highly abnormal mRNA profile, including the persistent expression of CD44 and CD25 markers characteristic of immature cells. We also observed that the p53 pathway became activated in these cells and that a deficiency of p53 partially rescued the defect in thymus cellularity (in contrast to early B cells) of Smarca5-deficient mice. However, the activation of p53 was not primarily responsible for the thymocyte developmental defects observed in the mutants. Our results indicate that Smarca5 plays a key role in the development of thymocytes undergoing β-selection, γδ thymocytes, and also B cell progenitors by regulating the transcription of early differentiation programs.
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http://dx.doi.org/10.4049/jimmunol.1801684DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6548592PMC
June 2019

Bidirectional Analysis of Cryba4-Crybb1 Nascent Transcription and Nuclear Accumulation of Crybb3 mRNAs in Lens Fibers.

Invest Ophthalmol Vis Sci 2019 01;60(1):234-244

Departments of Genetics, Albert Einstein College of Medicine, Bronx, New York, United States.

Purpose: Crystallin gene expression during lens fiber cell differentiation is tightly spatially and temporally regulated. A significant fraction of mammalian genes is transcribed from adjacent promoters in opposite directions ("bidirectional" promoters). It is not known whether two proximal genes located on the same allele are simultaneously transcribed.

Methods: Mouse lens transcriptome was analyzed for paired genes whose transcriptional start sites are separated by less than 5 kbp to identify coexpressed bidirectional promoter gene pairs. To probe these transcriptional mechanisms, nascent transcription of Cryba4, Crybb1, and Crybb3 genes from gene-rich part of chromosome 5 was visualized by RNA fluorescent in situ hybridizations (RNA FISH) in individual lens fiber cell nuclei.

Results: Genome-wide lens transcriptome analysis by RNA-seq revealed that the Cryba4-Crybb1 pair has the highest Pearson correlation coefficient between their steady-state mRNA levels. Analysis of Cryba4 and Crybb1 nascent transcription revealed frequent simultaneous expression of both genes from the same allele. Nascent Crybb3 transcript visualization in "early" but not "late" differentiating lens fibers show nuclear accumulation of the spliced Crybb3 transcripts that was not affected in abnormal lens fiber cell nuclei depleted of chromatin remodeling enzyme Snf2h (Smarca5).

Conclusions: The current study shows for the first time that two highly expressed lens crystallin genes, Cryba4 and Crybb1, can be simultaneously transcribed from adjacent bidirectional promoters and do not show nuclear accumulation. In contrast, spliced Crybb3 mRNAs transiently accumulate in early lens fiber cell nuclei. The gene pairs coexpressed during lens development showed significant enrichment in human "cataract" phenotype.
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http://dx.doi.org/10.1167/iovs.18-25921DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6336207PMC
January 2019

Transcriptional burst fraction and size dynamics during lens fiber cell differentiation and detailed insights into the denucleation process.

J Biol Chem 2018 08 29;293(34):13176-13190. Epub 2018 Jun 29.

From the Departments of Genetics,

Genes are transcribed in irregular pulses of activity termed transcriptional bursts. Cellular differentiation requires coordinated gene expression; however, it is unknown whether the burst fraction ( the number of active phases of transcription) or size/intensity (the number of RNA molecules produced within a burst) changes during cell differentiation. In the ocular lens, the positions of lens fiber cells correlate precisely with their differentiation status, and the most advanced cells degrade their nuclei. Here, we examined the transcriptional parameters of the β-actin and lens differentiation-specific α-, β-, and γ-crystallin genes by RNA fluorescent hybridization (FISH) in the lenses of embryonic day (E) E12.5, E14.5, and E16.5 mouse embryos and newborns. We found that cellular differentiation dramatically alters the burst fraction in synchronized waves across the lens fiber cell compartment with less dramatic changes in burst intensity. Surprisingly, we observed nascent transcription of multiple genes in nuclei just before nuclear destruction. Nuclear condensation was accompanied by transfer of nuclear proteins, including histone and nonhistone proteins, to the cytoplasm. Although lens-specific deletion of the chromatin remodeler SWI/SNF-related matrix-associated actin-dependent regulator of chromatin subfamily A member 5 (Smarca5/Snf2h) interfered with denucleation, persisting nuclei remained transcriptionally competent and exhibited changes in both burst intensity and fraction depending on the gene examined. Our results uncover the mechanisms of nascent transcriptional control during differentiation and chromatin remodeling, confirm the burst fraction as the major factor adjusting gene expression levels, and reveal transcriptional competence of fiber cell nuclei even as they approach disintegration.
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http://dx.doi.org/10.1074/jbc.RA118.001927DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6109918PMC
August 2018

Emerging roles of linker histones in regulating chromatin structure and function.

Nat Rev Mol Cell Biol 2018 03 11;19(3):192-206. Epub 2017 Oct 11.

Laboratory of Biochemistry and Molecular Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.

Together with core histones, which make up the nucleosome, the linker histone (H1) is one of the five main histone protein families present in chromatin in eukaryotic cells. H1 binds to the nucleosome to form the next structural unit of metazoan chromatin, the chromatosome, which may help chromatin to fold into higher-order structures. Despite their important roles in regulating the structure and function of chromatin, linker histones have not been studied as extensively as core histones. Nevertheless, substantial progress has been made recently. The first near-atomic resolution crystal structure of a chromatosome core particle and an 11 Å resolution cryo-electron microscopy-derived structure of the 30 nm nucleosome array have been determined, revealing unprecedented details about how linker histones interact with the nucleosome and organize higher-order chromatin structures. Moreover, several new functions of linker histones have been discovered, including their roles in epigenetic regulation and the regulation of DNA replication, DNA repair and genome stability. Studies of the molecular mechanisms of H1 action in these processes suggest a new paradigm for linker histone function beyond its architectural roles in chromatin.
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http://dx.doi.org/10.1038/nrm.2017.94DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5897046PMC
March 2018

Regulatory functions and chromatin loading dynamics of linker histone H1 during endoreplication in .

Genes Dev 2017 03;31(6):603-616

Department of Cell Biology, Albert Einstein College of Medicine, Bronx, New York 10461, USA.

Eukaryotic DNA replicates asynchronously, with discrete genomic loci replicating during different stages of S phase. larval tissues undergo endoreplication without cell division, and the latest replicating regions occasionally fail to complete endoreplication, resulting in underreplicated domains of polytene chromosomes. Here we show that linker histone H1 is required for the underreplication (UR) phenomenon in salivary glands. H1 directly interacts with the Suppressor of UR (SUUR) protein and is required for SUUR binding to chromatin in vivo. These observations implicate H1 as a critical factor in the formation of underreplicated regions and an upstream effector of SUUR. We also demonstrate that the localization of H1 in chromatin changes profoundly during the endocycle. At the onset of endocycle S (endo-S) phase, H1 is heavily and specifically loaded into late replicating genomic regions and is then redistributed during the course of endoreplication. Our data suggest that cell cycle-dependent chromosome occupancy of H1 is governed by several independent processes. In addition to the ubiquitous replication-related disassembly and reassembly of chromatin, H1 is deposited into chromatin through a novel pathway that is replication-independent, rapid, and locus-specific. This cell cycle-directed dynamic localization of H1 in chromatin may play an important role in the regulation of DNA replication timing.
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http://dx.doi.org/10.1101/gad.295717.116DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5393055PMC
March 2017

The ISWI ATPase Smarca5 (Snf2h) Is Required for Proliferation and Differentiation of Hematopoietic Stem and Progenitor Cells.

Stem Cells 2017 06 15;35(6):1614-1623. Epub 2017 Apr 15.

BIOCEV, First Faculty of Medicine, Charles University, Czech Republic.

The imitation switch nuclear ATPase Smarca5 (Snf2h) is one of the most conserved chromatin remodeling factors. It exists in a variety of oligosubunit complexes that move DNA with respect to the histone octamer to generate regularly spaced nucleosomal arrays. Smarca5 interacts with different accessory proteins and represents a molecular motor for DNA replication, repair, and transcription. We deleted Smarca5 at the onset of definitive hematopoiesis (Vav1-iCre) and observed that animals die during late fetal development due to anemia. Hematopoietic stem and progenitor cells accumulated but their maturation toward erythroid and myeloid lineages was inhibited. Proerythroblasts were dysplastic while basophilic erythroblasts were blocked in G2/M and depleted. Smarca5 deficiency led to increased p53 levels, its activation at two residues, one associated with DNA damage (S15 ° ) second with CBP/p300 (K376 ), and finally activation of the p53 targets. We also deleted Smarca5 in committed erythroid cells (Epor-iCre) and observed that animals were anemic postnatally. Furthermore, 4-hydroxytamoxifen-mediated deletion of Smarca5 in the ex vivo cultures confirmed its requirement for erythroid cell proliferation. Thus, Smarca5 plays indispensable roles during early hematopoiesis and erythropoiesis. Stem Cells 2017;35:1614-1623.
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http://dx.doi.org/10.1002/stem.2604DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5927548PMC
June 2017

BEN domain protein Elba2 can functionally substitute for linker histone H1 in Drosophila in vivo.

Sci Rep 2016 Sep 30;6:34354. Epub 2016 Sep 30.

Albert Einstein College of Medicine, Department of Cell Biology, Bronx, NY 10461, USA.

Metazoan linker histones are essential for development and play crucial roles in organization of chromatin, modification of epigenetic states and regulation of genetic activity. Vertebrates express multiple linker histone H1 isoforms, which may function redundantly. In contrast, H1 isoforms are not present in Dipterans, including D. melanogaster, except for an embryo-specific, distantly related dBigH1. Here we show that Drosophila BEN domain protein Elba2, which is expressed in early embryos and was hypothesized to have insulator-specific functions, can compensate for the loss of H1 in vivo. Although the Elba2 gene is not essential, its mutation causes a disruption of normal internucleosomal spacing of chromatin and reduced nuclear compaction in syncytial embryos. Elba2 protein is distributed ubiquitously in polytene chromosomes and strongly colocalizes with H1. In H1-depleted animals, ectopic expression of Elba2 rescues the increased lethality and ameliorates abnormalities of chromosome architecture and heterochromatin functions. We also demonstrate that ectopic expression of BigH1 similarly complements the deficiency of H1 protein. Thus, in organisms that do not express redundant H1 isoforms, the structural and biological functions performed by canonical linker histones in later development, may be shared in early embryos by weakly homologous proteins, such as BigH1, or even unrelated, non-homologous proteins, such as Elba2.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5043383PMC
http://dx.doi.org/10.1038/srep34354DOI Listing
September 2016

Chromatin remodeling enzyme Snf2h regulates embryonic lens differentiation and denucleation.

Development 2016 06;143(11):1937-47

Department of Ophthalmology & Visual Sciences and Genetics, Albert Einstein College of Medicine, Bronx, NY 10461, USA

Ocular lens morphogenesis is a model for investigating mechanisms of cellular differentiation, spatial and temporal gene expression control, and chromatin regulation. Brg1 (Smarca4) and Snf2h (Smarca5) are catalytic subunits of distinct ATP-dependent chromatin remodeling complexes implicated in transcriptional regulation. Previous studies have shown that Brg1 regulates both lens fiber cell differentiation and organized degradation of their nuclei (denucleation). Here, we employed a conditional Snf2h(flox) mouse model to probe the cellular and molecular mechanisms of lens formation. Depletion of Snf2h induces premature and expanded differentiation of lens precursor cells forming the lens vesicle, implicating Snf2h as a key regulator of lens vesicle polarity through spatial control of Prox1, Jag1, p27(Kip1) (Cdkn1b) and p57(Kip2) (Cdkn1c) gene expression. The abnormal Snf2h(-/-) fiber cells also retain their nuclei. RNA profiling of Snf2h(-/) (-) and Brg1(-/-) eyes revealed differences in multiple transcripts, including prominent downregulation of those encoding Hsf4 and DNase IIβ, which are implicated in the denucleation process. In summary, our data suggest that Snf2h is essential for the establishment of lens vesicle polarity, partitioning of prospective lens epithelial and fiber cell compartments, lens fiber cell differentiation, and lens fiber cell nuclear degradation.
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http://dx.doi.org/10.1242/dev.135285DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4920164PMC
June 2016

Independent Biological and Biochemical Functions for Individual Structural Domains of Drosophila Linker Histone H1.

J Biol Chem 2016 07 18;291(29):15143-55. Epub 2016 May 18.

From the Department of Cell Biology, Albert Einstein College of Medicine, Bronx, New York 10461

Linker histone H1 is among the most abundant components of chromatin. H1 has profound effects on chromosome architecture. H1 also helps to tether DNA- and histone-modifying enzymes to chromatin. Metazoan linker histones have a conserved tripartite structure comprising N-terminal, globular, and long, unstructured C-terminal domains. Here we utilize truncated Drosophila H1 polypeptides in vitro and H1 mutant transgenes in vivo to interrogate the roles of these domains in multiple biochemical and biological activities of H1. We demonstrate that the globular domain and the proximal part of the C-terminal domain are essential for H1 deposition into chromosomes and for the stability of H1-chromatin binding. The two domains are also essential for fly viability and the establishment of a normal polytene chromosome structure. Additionally, through interaction with the heterochromatin-specific histone H3 Lys-9 methyltransferase Su(var)3-9, the H1 C-terminal domain makes important contributions to formation and H3K9 methylation of heterochromatin as well as silencing of transposons in heterochromatin. Surprisingly, the N-terminal domain does not appear to be required for any of these functions. However, it is involved in the formation of a single chromocenter in polytene chromosomes. In summary, we have discovered that linker histone H1, similar to core histones, exerts its multiple biological functions through independent, biochemically separable activities of its individual structural domains.
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http://dx.doi.org/10.1074/jbc.M116.730705DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4946930PMC
July 2016

Local compartment changes and regulatory landscape alterations in histone H1-depleted cells.

Genome Biol 2015 Dec 23;16:289. Epub 2015 Dec 23.

Hubrecht Institute-KNAW & University Medical Center Utrecht, Uppsalalaan 8, 3584, CT, Utrecht, The Netherlands.

Background: Linker histone H1 is a core chromatin component that binds to nucleosome core particles and the linker DNA between nucleosomes. It has been implicated in chromatin compaction and gene regulation and is anticipated to play a role in higher-order genome structure. Here we have used a combination of genome-wide approaches including DNA methylation, histone modification and DNase I hypersensitivity profiling as well as Hi-C to investigate the impact of reduced cellular levels of histone H1 in embryonic stem cells on chromatin folding and function.

Results: We find that depletion of histone H1 changes the epigenetic signature of thousands of potential regulatory sites across the genome. Many of them show cooperative loss or gain of multiple chromatin marks. Epigenetic alterations cluster to gene-dense topologically associating domains (TADs) that already showed a high density of corresponding chromatin features. Genome organization at the three-dimensional level is largely intact, but we find changes in the structural segmentation of chromosomes specifically for the epigenetically most modified TADs.

Conclusions: Our data show that cells require normal histone H1 levels to expose their proper regulatory landscape. Reducing the levels of histone H1 results in massive epigenetic changes and altered topological organization particularly at the most active chromosomal domains. Changes in TAD configuration coincide with epigenetic landscape changes but not with transcriptional output changes, supporting the emerging concept that transcriptional control and nuclear positioning of TADs are not causally related but independently controlled by the locally associated trans-acting factors.
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http://dx.doi.org/10.1186/s13059-015-0857-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4699363PMC
December 2015

A genetic screen and transcript profiling reveal a shared regulatory program for Drosophila linker histone H1 and chromatin remodeler CHD1.

G3 (Bethesda) 2015 Jan 27;5(4):677-87. Epub 2015 Jan 27.

Department of Cell Biology, Albert Einstein College of Medicine, Bronx, New York 10461

Chromatin structure and activity can be modified through ATP-dependent repositioning of nucleosomes and posttranslational modifications of core histone tails within nucleosome core particles and by deposition of linker histones into the oligonucleosome fiber. The linker histone H1 is essential in metazoans. It has a profound effect on organization of chromatin into higher-order structures and on recruitment of histone-modifying enzymes to chromatin. Here, we describe a genetic screen for modifiers of the lethal phenotype caused by depletion of H1 in Drosophila melanogaster. We identify 41 mis-expression alleles that enhance and 20 that suppress the effect of His1 depletion in vivo. Most of them are important for chromosome organization, transcriptional regulation, and cell signaling. Specifically, the reduced viability of H1-depleted animals is strongly suppressed by ubiquitous mis-expression of the ATP-dependent chromatin remodeling enzyme CHD1. Comparison of transcript profiles in H1-depleted and Chd1 null mutant larvae revealed that H1 and CHD1 have common transcriptional regulatory programs in vivo. H1 and CHD1 share roles in repression of numerous developmentally regulated and extracellular stimulus-responsive transcripts, including immunity-related and stress response-related genes. Thus, linker histone H1 participates in various regulatory programs in chromatin to alter gene expression.
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http://dx.doi.org/10.1534/g3.115.016709DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4390582PMC
January 2015

Drosophila linker histone H1 coordinates STAT-dependent organization of heterochromatin and suppresses tumorigenesis caused by hyperactive JAK-STAT signaling.

Epigenetics Chromatin 2014 28;7:16. Epub 2014 Jul 28.

Department of Cell Biology, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA.

Background: Within the nucleus of eukaryotic cells, chromatin is organized into compact, silent regions called heterochromatin and more loosely packaged regions of euchromatin where transcription is more active. Although the existence of heterochromatin has been known for many years, the cellular factors responsible for its formation have only recently been identified. Two key factors involved in heterochromatin formation in Drosophila are the H3 lysine 9 methyltransferase Su(var)3-9 and heterochromatin protein 1 (HP1). The linker histone H1 also plays a major role in heterochromatin formation in Drosophila by interacting with Su(var)3-9 and helping to recruit it to heterochromatin. Drosophila STAT (Signal transducer and activator of transcription) (STAT92E) has also been shown to be involved in the maintenance of heterochromatin, but its relationship to the H1-Su(var)3-9 heterochromatin pathway is unknown. STAT92E is also involved in tumor formation in flies. Hyperactive Janus kinase (JAK)-STAT signaling due to a mutation in Drosophila JAK (Hopscotch) causes hematopoietic tumors.

Results: We show here that STAT92E is a second partner of H1 in the regulation of heterochromatin structure. H1 physically interacts with STAT92E and regulates its ectopic localization in the chromatin. Mis-localization of STAT92E due to its hyperphosphorylation or H1 depletion disrupts heterochromatin integrity. The contribution of the H1-STAT pathway to heterochromatin formation is mechanistically distinct from that of H1 and Su(var)3-9. The recruitment of STAT92E to chromatin by H1 also plays an important regulatory role in JAK-STAT induced tumors in flies. Depleting the linker histone H1 in flies carrying the oncogenic hopscotch (Tum-l) allele enhances tumorigenesis, and H1 overexpression suppresses tumorigenesis.

Conclusions: Our results suggest the existence of two independent pathways for heterochromatin formation in Drosophila, one involving Su(var)3-9 and HP1 and the other involving STAT92E and HP1. The H1 linker histone directs both pathways through physical interactions with Su(var)3-9 and STAT92E, as well with HP1. The physical interaction of H1 and STAT92E confers a regulatory role on H1 in JAK-STAT signaling. H1 serves as a molecular reservoir for STAT92E in chromatin, enabling H1 to act as a tumor suppressor and oppose an oncogenic mutation in the JAK-STAT signaling pathway.
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http://dx.doi.org/10.1186/1756-8935-7-16DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4149798PMC
September 2014

Snf2h-mediated chromatin organization and histone H1 dynamics govern cerebellar morphogenesis and neural maturation.

Nat Commun 2014 Jun 20;5:4181. Epub 2014 Jun 20.

1] Regenerative Medicine Program, Ottawa Hospital Research Institute, Ottawa, Ontario, Canada K1H 8L6 [2] Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada K1H 8M5 [3] Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, Ontario, Canada K1H 8M5.

Chromatin compaction mediates progenitor to post-mitotic cell transitions and modulates gene expression programs, yet the mechanisms are poorly defined. Snf2h and Snf2l are ATP-dependent chromatin remodelling proteins that assemble, reposition and space nucleosomes, and are robustly expressed in the brain. Here we show that mice conditionally inactivated for Snf2h in neural progenitors have reduced levels of histone H1 and H2A variants that compromise chromatin fluidity and transcriptional programs within the developing cerebellum. Disorganized chromatin limits Purkinje and granule neuron progenitor expansion, resulting in abnormal post-natal foliation, while deregulated transcriptional programs contribute to altered neural maturation, motor dysfunction and death. However, mice survive to young adulthood, in part from Snf2l compensation that restores Engrailed-1 expression. Similarly, Purkinje-specific Snf2h ablation affects chromatin ultrastructure and dendritic arborization, but alters cognitive skills rather than motor control. Our studies reveal that Snf2h controls chromatin organization and histone H1 dynamics for the establishment of gene expression programs underlying cerebellar morphogenesis and neural maturation.
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http://dx.doi.org/10.1038/ncomms5181DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4083431PMC
June 2014

The role of H1 linker histone subtypes in preserving the fidelity of elaboration of mesendodermal and neuroectodermal lineages during embryonic development.

PLoS One 2014 6;9(5):e96858. Epub 2014 May 6.

Roslyn and Leslie Goldstein Laboratory for Stem Cell Biology and Regenerative Medicine, Albert Einstein College of Medicine, Bronx, New York, United States of America; Institute for Brain Disorders and Neural Regeneration, Albert Einstein College of Medicine, Bronx, New York, United States of America; Department of Neurology, Albert Einstein College of Medicine, Bronx, New York, United States of America; Department of Neuroscience, Albert Einstein College of Medicine, Bronx, New York, United States of America; Department of Psychiatry and Behavioral Sciences, Albert Einstein College of Medicine, Bronx, New York, United States of America; Rose F. Kennedy Center for Research on Intellectual and Developmental Disabilities, Albert Einstein College of Medicine, Bronx, New York, United States of America; Einstein Cancer Center, Albert Einstein College of Medicine, Bronx, New York, United States of America; Ruth L. and David S. Gottesman Institute for Stem Cell Biology and Regenerative Medicine, Albert Einstein College of Medicine, Bronx, New York, United States of America; Center for Epigenomics, Albert Einstein College of Medicine, Bronx, New York, United States of America; Institute for Aging Research, Albert Einstein College of Medicine, Bronx, New York, United States of America.

H1 linker histone proteins are essential for the structural and functional integrity of chromatin and for the fidelity of additional epigenetic modifications. Deletion of H1c, H1d and H1e in mice leads to embryonic lethality by mid-gestation with a broad spectrum of developmental alterations. To elucidate the cellular and molecular mechanisms underlying H1 linker histone developmental functions, we analyzed embryonic stem cells (ESCs) depleted of H1c, H1d and H1e subtypes (H1-KO ESCs) by utilizing established ESC differentiation paradigms. Our study revealed that although H1-KO ESCs continued to express core pluripotency genes and the embryonic stem cell markers, alkaline phosphatase and SSEA1, they exhibited enhanced cell death during embryoid body formation and during specification of mesendoderm and neuroectoderm. In addition, we demonstrated deregulation in the developmental programs of cardiomyocyte, hepatic and pancreatic lineage elaboration. Moreover, ectopic neurogenesis and cardiomyogenesis occurred during endoderm-derived pancreatic but not hepatic differentiation. Furthermore, neural differentiation paradigms revealed selective impairments in the specification and maturation of glutamatergic and dopaminergic neurons with accelerated maturation of glial lineages. These impairments were associated with deregulation in the expression profiles of pro-neural genes in dorsal and ventral forebrain-derived neural stem cell species. Taken together, these experimental observations suggest that H1 linker histone proteins are critical for the specification, maturation and fidelity of organ-specific cellular lineages derived from the three cardinal germ layers.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0096858PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4011883PMC
June 2015

Developmentally regulated linker histone H1c promotes heterochromatin condensation and mediates structural integrity of rod photoreceptors in mouse retina.

J Biol Chem 2013 Jun 3;288(24):17895-907. Epub 2013 May 3.

Department of Neural and Behavioral Sciences, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA.

Mature rod photoreceptor cells contain very small nuclei with tightly condensed heterochromatin. We observed that during mouse rod maturation, the nucleosomal repeat length increases from 190 bp at postnatal day 1 to 206 bp in the adult retina. At the same time, the total level of linker histone H1 increased reaching the ratio of 1.3 molecules of total H1 per nucleosome, mostly via a dramatic increase in H1c. Genetic elimination of the histone H1c gene is functionally compensated by other histone variants. However, retinas in H1c/H1e/H1(0) triple knock-outs have photoreceptors with bigger nuclei, decreased heterochromatin area, and notable morphological changes suggesting that the process of chromatin condensation and rod cell structural integrity are partly impaired. In triple knock-outs, nuclear chromatin exposed several epigenetic histone modification marks masked in the wild type chromatin. Dramatic changes in exposure of a repressive chromatin mark, H3K9me2, indicate that during development linker histone plays a role in establishing the facultative heterochromatin territory and architecture in the nucleus. During retina development, the H1c gene and its promoter acquired epigenetic patterns typical of rod-specific genes. Our data suggest that histone H1c gene expression is developmentally up-regulated to promote facultative heterochromatin in mature rod photoreceptors.
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http://dx.doi.org/10.1074/jbc.M113.452144DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3682587PMC
June 2013

Drosophila H1 regulates the genetic activity of heterochromatin by recruitment of Su(var)3-9.

Science 2013 Apr;340(6128):78-81

Department of Cell Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.

Eukaryotic genomes harbor transposable elements and other repetitive sequences that must be silenced. Small RNA interference pathways play a major role in their repression. Here, we reveal another mechanism for silencing these sequences in Drosophila. Depleting the linker histone H1 in vivo leads to strong activation of these elements. H1-mediated silencing occurs in combination with the heterochromatin-specific histone H3 lysine 9 methyltransferase Su(var)3-9. H1 physically interacts with Su(var)3-9 and recruits it to chromatin in vitro, which promotes H3 methylation. We propose that H1 plays a key role in silencing by tethering Su(var)3-9 to heterochromatin. The tethering function of H1 adds to its established role as a regulator of chromatin compaction and accessibility.
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http://dx.doi.org/10.1126/science.1234654DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3756538PMC
April 2013

H1 linker histone promotes epigenetic silencing by regulating both DNA methylation and histone H3 methylation.

Proc Natl Acad Sci U S A 2013 Jan 9;110(5):1708-13. Epub 2013 Jan 9.

Department of Cell Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.

Epigenetic silencing in mammals involves DNA methylation and posttranslational modifications of core histones. Here we show that the H1 linker histone plays a key role in regulating both DNA methylation and histone H3 methylation at the H19 and Gtl2 loci in mouse ES cells. Some, but not all, murine H1 subtypes interact with DNA methyltransferases DNMT1 and DNMT3B. The interactions are direct and require a portion of the H1 C-terminal domain. Expression of an H1 subtype that interacts with DNMT1 and DNMT3B in ES cells leads to their recruitment and DNA methylation of the H19 and Gtl2 imprinting control regions. H1 also interferes with binding of the SET7/9 histone methyltransferase to the imprinting control regions, inhibiting production of an activating methylation mark on histone H3 lysine 4. H1-dependent recruitment of DNMT1 and DNMT3B and interference with the binding of SET7/9 also were observed with chromatin reconstituted in vitro. The data support a model in which H1 plays an active role in helping direct two processes that lead to the formation of epigenetic silencing marks. The data also provide evidence for functional differences among the H1 subtypes expressed in somatic mammalian cells.
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http://dx.doi.org/10.1073/pnas.1213266110DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3562819PMC
January 2013

A core erythroid transcriptional network is repressed by a master regulator of myelo-lymphoid differentiation.

Proc Natl Acad Sci U S A 2012 Mar 22;109(10):3832-7. Epub 2012 Feb 22.

Department of Cell Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.

Two mechanisms that play important roles in cell fate decisions are control of a "core transcriptional network" and repression of alternative transcriptional programs by antagonizing transcription factors. Whether these two mechanisms operate together is not known. Here we report that GATA-1, SCL, and Klf1 form an erythroid core transcriptional network by co-occupying >300 genes. Importantly, we find that PU.1, a negative regulator of terminal erythroid differentiation, is a highly integrated component of this network. GATA-1, SCL, and Klf1 act to promote, whereas PU.1 represses expression of many of the core network genes. PU.1 also represses the genes encoding GATA-1, SCL, Klf1, and important GATA-1 cofactors. Conversely, in addition to repressing PU.1 expression, GATA-1 also binds to and represses >100 PU.1 myelo-lymphoid gene targets in erythroid progenitors. Mathematical modeling further supports that this dual mechanism of repressing both the opposing upstream activator and its downstream targets provides a synergistic, robust mechanism for lineage specification. Taken together, these results amalgamate two key developmental principles, namely, regulation of a core transcriptional network and repression of an alternative transcriptional program, thereby enhancing our understanding of the mechanisms that establish cellular identity.
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http://dx.doi.org/10.1073/pnas.1121019109DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3309740PMC
March 2012

Histone H1 recruitment by CHD8 is essential for suppression of the Wnt-β-catenin signaling pathway.

Mol Cell Biol 2012 Jan 14;32(2):501-12. Epub 2011 Nov 14.

Department of Molecular and Cellular Biology, Medical Institute of Bioregulation, Kyushu University, Fukuoka, Japan.

Members of the chromodomain helicase DNA-binding (CHD) family of proteins are thought to regulate gene expression. Among mammalian CHD proteins, CHD8 was originally isolated as a negative regulator of the Wnt-β-catenin signaling pathway that binds directly to β-catenin and suppresses its transactivation activity. The mechanism by which CHD8 inhibits β-catenin-dependent transcription has been unclear, however. Here we show that CHD8 promotes the association of β-catenin and histone H1, with formation of the trimeric complex on chromatin being required for inhibition of β-catenin-dependent transactivation. A CHD8 mutant that lacks the histone H1 binding domain did not show such inhibitory activity, indicating that histone H1 recruitment is essential for the inhibitory effect of CHD8. Furthermore, either depletion of histone H1 or expression of a dominant negative mutant of this protein resulted in enhancement of the response to Wnt signaling. These observations reveal a new mode of regulation of the Wnt signaling pathway by CHD8, which counteracts β-catenin function through recruitment of histone H1 to Wnt target genes. Given that CHD8 is expressed predominantly during embryogenesis, it may thus contribute to setting a threshold for responsiveness to Wnt signaling that operates in a development-dependent manner.
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http://dx.doi.org/10.1128/MCB.06409-11DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3255766PMC
January 2012

A large gene network in immature erythroid cells is controlled by the myeloid and B cell transcriptional regulator PU.1.

PLoS Genet 2011 Jun 9;7(6):e1001392. Epub 2011 Jun 9.

Department of Cell Biology, Albert Einstein College of Medicine, Bronx, New York, United States of America.

PU.1 is a hematopoietic transcription factor that is required for the development of myeloid and B cells. PU.1 is also expressed in erythroid progenitors, where it blocks erythroid differentiation by binding to and inhibiting the main erythroid promoting factor, GATA-1. However, other mechanisms by which PU.1 affects the fate of erythroid progenitors have not been thoroughly explored. Here, we used ChIP-Seq analysis for PU.1 and gene expression profiling in erythroid cells to show that PU.1 regulates an extensive network of genes that constitute major pathways for controlling growth and survival of immature erythroid cells. By analyzing fetal liver erythroid progenitors from mice with low PU.1 expression, we also show that the earliest erythroid committed cells are dramatically reduced in vivo. Furthermore, we find that PU.1 also regulates many of the same genes and pathways in other blood cells, leading us to propose that PU.1 is a multifaceted factor with overlapping, as well as distinct, functions in several hematopoietic lineages.
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http://dx.doi.org/10.1371/journal.pgen.1001392DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3111485PMC
June 2011

The rhox homeobox gene cluster is imprinted and selectively targeted for regulation by histone h1 and DNA methylation.

Mol Cell Biol 2011 Mar 18;31(6):1275-87. Epub 2011 Jan 18.

Department of Reproductive Medicine, University of California-San Diego School of Medicine, La Jolla, CA 92093, USA.

Histone H1 is an abundant and essential component of chromatin whose precise role in regulating gene expression is poorly understood. Here, we report that a major target of H1-mediated regulation in embryonic stem (ES) cells is the X-linked Rhox homeobox gene cluster. To address the underlying mechanism, we examined the founding member of the Rhox gene cluster-Rhox5-and found that its distal promoter (Pd) loses H1, undergoes demethylation, and is transcriptionally activated in response to loss of H1 genes in ES cells. Demethylation of the Pd is required for its transcriptional induction and we identified a single cytosine in the Pd that, when methylated, is sufficient to inhibit Pd transcription. Methylation of this single cytosine prevents the Pd from binding GA-binding protein (GABP), a transcription factor essential for Pd transcription. Thus, H1 silences Rhox5 transcription by promoting methylation of one of its promoters, a mechanism likely to extend to other H1-regulated Rhox genes, based on analysis of ES cells lacking DNA methyltransferases. The Rhox cluster genes targeted for H1-mediated transcriptional repression are also subject to another DNA methylation-regulated process: Xp imprinting. Remarkably, we found that only H1-regulated Rhox genes are imprinted, not those immune to H1-mediated repression. Together, our results indicate that the Rhox gene cluster is a major target of H1-mediated transcriptional repression in ES cells and that H1 is a candidate to have a role in Xp imprinting.
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http://dx.doi.org/10.1128/MCB.00734-10DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3067900PMC
March 2011

Loss of Goosecoid-like and DiGeorge syndrome critical region 14 in interpeduncular nucleus results in altered regulation of rapid eye movement sleep.

Proc Natl Acad Sci U S A 2010 Oct 4;107(42):18155-60. Epub 2010 Oct 4.

Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.

Sleep and wakefulness are regulated primarily by inhibitory interactions between the hypothalamus and brainstem. The expression of the states of rapid eye movement (REM) sleep and non-REM (NREM) sleep also are correlated with the activity of groups of REM-off and REM-on neurons in the dorsal brainstem. However, the contribution of ventral brainstem nuclei to sleep regulation has been little characterized to date. Here we examined sleep and wakefulness in mice deficient in a homeobox transcription factor, Goosecoid-like (Gscl), which is one of the genes deleted in DiGeorge syndrome or 22q11 deletion syndrome. The expression of Gscl is restricted to the interpeduncular nucleus (IP) in the ventral region of the midbrain-hindbrain transition. The IP has reciprocal connections with several cell groups implicated in sleep/wakefulness regulation. Although Gscl(-/-) mice have apparently normal anatomy and connections of the IP, they exhibited a reduced total time spent in REM sleep and fewer REM sleep episodes. In addition, Gscl(-/-) mice showed reduced theta power during REM sleep and increased arousability during REM sleep. Gscl(-/-) mice also lacked the expression of DiGeorge syndrome critical region 14 (Dgcr14) in the IP. These results indicate that the absence of Gscl and Dgcr14 in the IP results in altered regulation of REM sleep.
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http://dx.doi.org/10.1073/pnas.1012764107DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2964225PMC
October 2010

GATA-1 directly regulates p21 gene expression during erythroid differentiation.

Cell Cycle 2010 May 15;9(10):1972-80. Epub 2010 May 15.

1Department of Cell Biology, Montefiore Medical Center, Bronx, NY, USA.

Lineage-determination transcription factors coordinate cell differentiation and proliferation by controlling the synthesis of lineage-specific gene products as well as cell cycle regulators. GATA-1 is a master regulator of erythropoiesis. Its role in regulating erythroid-specific genes has been extensively studied, whereas its role in controlling genes that regulate cell proliferation is less understood. Ectopic expression of GATA-1 in erythroleukemia cells releases the block to their differentiation and leads to terminal cell division. An early event in reprogramming the erythroleukemia cells is induction of the cyclin-dependent kinase inhibitor p21. Remarkably, ectopic expression of p21 also induces the erythroleukemia cells to differentiate. We now report that GATA-1 directly regulates transcription of the p21 gene in both erythroleukemia cells and normal erythroid progenitors. Using reporter, electrophoretic mobility shift, and chromatin immunoprecipitation assays, we show that GATA-1 stimulates p21 gene transcription by binding to consensus binding sites in the upstream region of the p21 gene promoter. This activity is also dependent on a binding site for Sp1/KLF-like factors near the transcription start site. Our findings indicate that p21 is a crucial downstream gene target and effector of GATA-1 during red blood cell terminal differentiation.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3019278PMC
http://dx.doi.org/10.4161/cc.9.10.11602DOI Listing
May 2010