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Cockrell AJ, Gerton JL. Nucleolar Organizer Regions as Transcription-Based Scaffolds of Nucleolar Structure and Function. Results Probl Cell Differ 2022; 70:551-580. [PMID: 36348121 DOI: 10.1007/978-3-031-06573-6_19] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
Eukaryotic genomes maintain multiple copies of ribosomal DNA gene repeats in tandem arrays to provide sufficient ribosomal RNAs to make ribosomes. These DNA repeats are the most highly transcribed regions of the genome, with dedicated transcriptional machinery to manage the enormous task of producing more than 50% of the total RNA in a proliferating cell. The arrays are called nucleolar organizer regions (NORs) and constitute the scaffold of the nucleolar compartment, where ribosome biogenesis occurs. Advances in molecular and cellular biology have brought great insights into how these arrays are transcribed and organized within genomes. Much of their biology is driven by their high transcription level, which has also driven the development of unique methods to understand rDNA gene activity, beginning with classic techniques such as silver staining and Miller spreads. However, the application of modern methodologies such as CRISPR gene editing, super-resolution microscopy, and long-read sequencing has enabled recent advances described herein, with many more discoveries possible soon. This chapter highlights what is known about NOR transcription and organization and the techniques applied historically and currently. Given the potential for NORs to impact organismal health and disease, as highlighted at the end of the chapter, the field must continue to develop and apply innovative analysis to understand genetic, epigenetic, and organizer properties of the ribosomal DNA repeats.
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Affiliation(s)
- Alexandria J Cockrell
- Stowers Institute for Medical Research, Kansas City, MO, USA
- Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, KS, USA
| | - Jennifer L Gerton
- Stowers Institute for Medical Research, Kansas City, MO, USA.
- Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, KS, USA.
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2
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Chromosome Dynamics Regulating Genomic Dispersion and Alteration of Nucleolus Organizer Regions (NORs). Cells 2020; 9:cells9040971. [PMID: 32326514 PMCID: PMC7227013 DOI: 10.3390/cells9040971] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2020] [Revised: 04/09/2020] [Accepted: 04/13/2020] [Indexed: 02/06/2023] Open
Abstract
The nucleolus organizer regions (NORs) demonstrate differences in genomic dispersion and transcriptional activity among all organisms. I postulate that such differences stem from distinct genomic structures and their interactions from chromosome observations using fluorescence in situ hybridization and silver nitrate staining methods. Examples in primates and Australian bulldog ants indicate that chromosomal features indeed play a significant role in determining the properties of NORs. In primates, rDNA arrays that are located on the short arm of acrocentrics frequently form reciprocal associations ("affinity"), but they lack such associations ("non-affinity") with other repeat arrays-a binary molecular effect. These "rules" of affinity vs. non-affinity are extrapolated from the chromosomal configurations of meiotic prophase. In bulldog ants, genomic dispersions of rDNA loci expand much more widely following an increase in the number of acrocentric chromosomes formed by centric fission. Affinity appears to be a significantly greater force: associations likely form among rDNA and heterochromatin arrays of acrocentrics-thus, more acrocentrics bring about more rDNA loci. The specific interactions among NOR-related genome structures remain unclear and require further investigation. Here, I propose that there are limited and non-limited genomic dispersion systems that result from genomic affinity rules, inducing specific chromosomal configurations that are related to NORs.
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3
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Cerqueira AV, Lemos B. Ribosomal DNA and the Nucleolus as Keystones of Nuclear Architecture, Organization, and Function. Trends Genet 2019; 35:710-723. [PMID: 31447250 DOI: 10.1016/j.tig.2019.07.011] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2019] [Revised: 07/23/2019] [Accepted: 07/25/2019] [Indexed: 12/12/2022]
Abstract
The multicopy ribosomal DNA (rDNA) array gives origin to the nucleolus, a large nonmembrane-bound organelle that occupies a substantial volume within the cell nucleus. The rDNA/nucleolus has emerged as a coordinating hub in which seemingly disparate cellular functions converge, and from which a variety of cellular and organismal phenotypes emerge. However, the role of the nucleolus as a determinant and organizer of nuclear architecture and other epigenetic states of the genome is not well understood. We discuss the role of rDNA and the nucleolus in nuclear organization and function - from nucleolus-associated domains (NADs) to the regulation of imprinted loci and X chromosome inactivation, as well as rDNA contact maps that anchor and position the rDNA relative to the rest of the genome. The influence of the nucleolus on nuclear organization undoubtedly modulates diverse biological processes from metabolism to cell proliferation, genome-wide gene expression, maintenance of epigenetic states, and aging.
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Affiliation(s)
- Amanda V Cerqueira
- Department of Environmental Health, Program in Molecular and Integrative Physiological Sciences, Harvard T.H. Chan School of Public Health, Boston, MA 02115, USA
| | - Bernardo Lemos
- Department of Environmental Health, Program in Molecular and Integrative Physiological Sciences, Harvard T.H. Chan School of Public Health, Boston, MA 02115, USA; Broad Institute of Harvard and MIT, Cambridge, MA 02142, USA.
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4
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Correll CC, Bartek J, Dundr M. The Nucleolus: A Multiphase Condensate Balancing Ribosome Synthesis and Translational Capacity in Health, Aging and Ribosomopathies. Cells 2019; 8:cells8080869. [PMID: 31405125 PMCID: PMC6721831 DOI: 10.3390/cells8080869] [Citation(s) in RCA: 68] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2019] [Revised: 07/31/2019] [Accepted: 08/06/2019] [Indexed: 12/21/2022] Open
Abstract
The nucleolus is the largest membrane-less structure in the eukaryotic nucleus. It is involved in the biogenesis of ribosomes, essential macromolecular machines responsible for synthesizing all proteins required by the cell. The assembly of ribosomes is evolutionarily conserved and is the most energy-consuming cellular process needed for cell growth, proliferation, and homeostasis. Despite the significance of this process, the intricate pathophysiological relationship between the nucleolus and protein synthesis has only recently begun to emerge. Here, we provide perspective on new principles governing nucleolar formation and the resulting multiphase organization driven by liquid-liquid phase separation. With recent advances in the structural analysis of ribosome formation, we highlight the current understanding of the step-wise assembly of pre-ribosomal subunits and the quality control required for proper function. Finally, we address how aging affects ribosome genesis and how genetic defects in ribosome formation cause ribosomopathies, complex diseases with a predisposition to cancer.
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Affiliation(s)
- Carl C Correll
- Center for Proteomics and Molecular Therapeutics, Rosalind Franklin University of Medicine & Science, North Chicago, IL 60064, USA.
| | - Jiri Bartek
- Danish Cancer Society Research Center, Genome Integrity Unit, DK-2100 Copenhagen, Denmark
- Division of Genome Biology, Department of Medical Biochemistry and Biophysics, Science for Life Laboratory, Karolinska Institute, SE-171 77 Stockholm, Sweden
| | - Miroslav Dundr
- Center for Cancer Cell Biology Immunology and Infection, Rosalind Franklin University of Medicine & Science, North Chicago, IL 60064, USA.
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5
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Genome Organization in and around the Nucleolus. Cells 2019; 8:cells8060579. [PMID: 31212844 PMCID: PMC6628108 DOI: 10.3390/cells8060579] [Citation(s) in RCA: 71] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2019] [Revised: 06/09/2019] [Accepted: 06/11/2019] [Indexed: 12/17/2022] Open
Abstract
The nucleolus is the largest substructure in the nucleus, where ribosome biogenesis takes place, and forms around the nucleolar organizer regions (NORs) that comprise ribosomal RNA (rRNA) genes. Each cell contains hundreds of rRNA genes, which are organized in three distinct chromatin and transcriptional states—silent, inactive and active. Increasing evidence indicates that the role of the nucleolus and rRNA genes goes beyond the control of ribosome biogenesis. Recent results highlighted the nucleolus as a compartment for the location and regulation of repressive genomic domains and, together with the nuclear lamina, represents the hub for the organization of the inactive heterochromatin. In this review, we aim to describe the crosstalk between the nucleolus and the rest of the genome and how distinct rRNA gene chromatin states affect nucleolus structure and are implicated in genome stability, genome architecture, and cell fate decision.
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6
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Abstract
The nucleolus as site of ribosome biogenesis holds a pivotal role in cell metabolism. It is composed of ribosomal DNA (rDNA), which is present as tandem arrays located in nucleolus organizer regions (NORs). In interphase cells, rDNA can be found inside and adjacent to nucleoli and the location is indicative for transcriptional activity of ribosomal genes-inactive rDNA (outside) versus active one (inside). Moreover, the nucleolus itself acts as a spatial organizer of non-nucleolar chromatin. Microscopy-based approaches offer the possibility to explore the spatially distinct localization of the different DNA populations in relation to the nucleolar structure. Recent technical developments in microscopy and preparatory methods may further our understanding of the functional architecture of nucleoli. This review will attempt to summarize the current understanding of mammalian nucleolar chromatin organization as seen from a microscopist's perspective.
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Affiliation(s)
- Christian Schöfer
- Division of Cell and Developmental Biology, Center for Anatomy and Cell Biology, Medical University of Vienna, Schwarzspanierstr. 17, 1090, Vienna, Austria.
| | - Klara Weipoltshammer
- Division of Cell and Developmental Biology, Center for Anatomy and Cell Biology, Medical University of Vienna, Schwarzspanierstr. 17, 1090, Vienna, Austria
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7
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Arias Escayola D, Neugebauer KM. Dynamics and Function of Nuclear Bodies during Embryogenesis. Biochemistry 2018; 57:2462-2469. [PMID: 29473743 DOI: 10.1021/acs.biochem.7b01262] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Nuclear bodies are RNA-rich membraneless organelles in the cell nucleus that concentrate specific sets of nuclear proteins and RNA-protein complexes. Nuclear bodies such as the nucleolus, Cajal body (CB), and the histone locus body (HLB) concentrate factors required for nuclear steps of RNA processing. Formation of these nuclear bodies occurs on genomic loci and is frequently associated with active sites of transcription. Whether nuclear body formation is dependent on a particular gene element, an active process such as transcription, or the nascent RNA present at gene loci is a topic of debate. Recently, this question has been addressed through studies in model organisms and their embryos. The switch from maternally provided RNA and protein to zygotic gene products in early embryos has been well characterized in a variety of organisms. This process, termed maternal-to-zygotic transition, provides an excellent model for studying formation of nuclear bodies before, during, and after the transcriptional activation of the zygotic genome. Here, we review findings in embryos that reveal key principles in the study of the formation and function of nucleoli, CBs, and HLBs. We propose that while particular gene elements may contribute to formation of these nuclear bodies, active transcription promotes maturation of nuclear bodies and efficient RNA processing within them.
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Affiliation(s)
- Dahyana Arias Escayola
- Molecular Biophysics and Biochemistry , Yale University , New Haven , Connecticut 06520-8114 , United States
| | - Karla M Neugebauer
- Molecular Biophysics and Biochemistry , Yale University , New Haven , Connecticut 06520-8114 , United States
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8
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Zhu Y, Gong K, Denholtz M, Chandra V, Kamps MP, Alber F, Murre C. Comprehensive characterization of neutrophil genome topology. Genes Dev 2017; 31:141-153. [PMID: 28167501 PMCID: PMC5322729 DOI: 10.1101/gad.293910.116] [Citation(s) in RCA: 57] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2016] [Accepted: 01/05/2017] [Indexed: 12/18/2022]
Abstract
Neutrophils are responsible for the first line of defense against invading pathogens. Their nuclei are uniquely structured as multiple lobes that establish a highly constrained nuclear environment. Here we found that neutrophil differentiation was not associated with large-scale changes in the number and sizes of topologically associating domains (TADs). However, neutrophil genomes were enriched for long-range genomic interactions that spanned multiple TADs. Population-based simulation of spherical and toroid genomes revealed declining radii of gyration for neutrophil chromosomes. We found that neutrophil genomes were highly enriched for heterochromatic genomic interactions across vast genomic distances, a process named supercontraction. Supercontraction involved genomic regions located in the heterochromatic compartment in both progenitors and neutrophils or genomic regions that switched from the euchromatic to the heterochromatic compartment during neutrophil differentiation. Supercontraction was accompanied by the repositioning of centromeres, pericentromeres, and long interspersed nuclear elements (LINEs) to the neutrophil nuclear lamina. We found that Lamin B receptor expression was required to attach centromeric and pericentromeric repeats but not LINE-1 elements to the lamina. Differentiating neutrophils also repositioned ribosomal DNA and mininucleoli to the lamina-a process that was closely associated with sharply reduced ribosomal RNA expression. We propose that large-scale chromatin reorganization involving supercontraction and recruitment of heterochromatin and nucleoli to the nuclear lamina facilitates the folding of the neutrophil genome into a confined geometry imposed by a multilobed nuclear architecture.
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Affiliation(s)
- Yina Zhu
- Department of Molecular Biology, University of California at San Diego, La Jolla, California 92093, USA
| | - Ke Gong
- Department of Biological Sciences, University of Southern California, Los Angeles, California 90089, USA
| | - Matthew Denholtz
- Department of Molecular Biology, University of California at San Diego, La Jolla, California 92093, USA
| | - Vivek Chandra
- Department of Molecular Biology, University of California at San Diego, La Jolla, California 92093, USA
| | - Mark P Kamps
- Department of Pathology, University of California at San Diego, La Jolla, California 92093, USA
| | - Frank Alber
- Department of Biological Sciences, University of Southern California, Los Angeles, California 90089, USA
| | - Cornelis Murre
- Department of Molecular Biology, University of California at San Diego, La Jolla, California 92093, USA
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9
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Sawyer IA, Sturgill D, Sung MH, Hager GL, Dundr M. Cajal body function in genome organization and transcriptome diversity. Bioessays 2016; 38:1197-1208. [PMID: 27767214 DOI: 10.1002/bies.201600144] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Nuclear bodies contribute to non-random organization of the human genome and nuclear function. Using a major prototypical nuclear body, the Cajal body, as an example, we suggest that these structures assemble at specific gene loci located across the genome as a result of high transcriptional activity. Subsequently, target genes are physically clustered in close proximity in Cajal body-containing cells. However, Cajal bodies are observed in only a limited number of human cell types, including neuronal and cancer cells. Ultimately, Cajal body depletion perturbs splicing kinetics by reducing target small nuclear RNA (snRNA) transcription and limiting the levels of spliceosomal snRNPs, including their modification and turnover following each round of RNA splicing. As such, Cajal bodies are capable of shaping the chromatin interaction landscape and the transcriptome by influencing spliceosome kinetics. Future studies should concentrate on characterizing the direct influence of Cajal bodies upon snRNA gene transcriptional dynamics. Also see the video abstract here.
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Affiliation(s)
- Iain A Sawyer
- Department of Cell Biology, Chicago Medical School, Rosalind Franklin University of Medicine and Science, North Chicago, IL, USA.,Laboratory of Receptor Biology and Gene Expression, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA
| | - David Sturgill
- Laboratory of Receptor Biology and Gene Expression, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA
| | - Myong-Hee Sung
- Laboratory of Molecular Biology and Immunology, National Institute on Aging, National Institutes of Health, Baltimore, MD, USA
| | - Gordon L Hager
- Laboratory of Receptor Biology and Gene Expression, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA
| | - Miroslav Dundr
- Department of Cell Biology, Chicago Medical School, Rosalind Franklin University of Medicine and Science, North Chicago, IL, USA
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10
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Population-based 3D genome structure analysis reveals driving forces in spatial genome organization. Proc Natl Acad Sci U S A 2016; 113:E1663-72. [PMID: 26951677 DOI: 10.1073/pnas.1512577113] [Citation(s) in RCA: 127] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Conformation capture technologies (e.g., Hi-C) chart physical interactions between chromatin regions on a genome-wide scale. However, the structural variability of the genome between cells poses a great challenge to interpreting ensemble-averaged Hi-C data, particularly for long-range and interchromosomal interactions. Here, we present a probabilistic approach for deconvoluting Hi-C data into a model population of distinct diploid 3D genome structures, which facilitates the detection of chromatin interactions likely to co-occur in individual cells. Our approach incorporates the stochastic nature of chromosome conformations and allows a detailed analysis of alternative chromatin structure states. For example, we predict and experimentally confirm the presence of large centromere clusters with distinct chromosome compositions varying between individual cells. The stability of these clusters varies greatly with their chromosome identities. We show that these chromosome-specific clusters can play a key role in the overall chromosome positioning in the nucleus and stabilizing specific chromatin interactions. By explicitly considering genome structural variability, our population-based method provides an important tool for revealing novel insights into the key factors shaping the spatial genome organization.
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11
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Abstract
Nucleoli are formed on the basis of ribosomal genes coding for RNAs of ribosomal particles, but also include a great variety of other DNA regions. In this article, we discuss the characteristics of ribosomal DNA: the structure of the rDNA locus, complex organization and functions of the intergenic spacer, multiplicity of gene copies in one cell, selective silencing of genes and whole gene clusters, relation to components of nucleolar ultrastructure, specific problems associated with replication. We also review current data on the role of non-ribosomal DNA in the organization and function of nucleoli. Finally, we discuss probable causes preventing efficient visualization of DNA in nucleoli.
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12
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Fritz A, Barutcu AR, Martin-Buley L, vanWijnen AJ, Zaidi SK, Imbalzano AN, Lian JB, Stein JL, Stein GS. Chromosomes at Work: Organization of Chromosome Territories in the Interphase Nucleus. J Cell Biochem 2016; 117:9-19. [PMID: 26192137 PMCID: PMC4715719 DOI: 10.1002/jcb.25280] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2015] [Accepted: 07/17/2015] [Indexed: 12/26/2022]
Abstract
The organization of interphase chromosomes in chromosome territories (CTs) was first proposed more than one hundred years ago. The introduction of increasingly sophisticated microscopic and molecular techniques, now provide complementary strategies for studying CTs in greater depth than ever before. Here we provide an overview of these strategies and how they are being used to elucidate CT interactions and the role of these dynamically regulated, nuclear-structure building blocks in directly supporting nuclear function in a physiologically responsive manner.
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Affiliation(s)
- Andrew Fritz
- University of Vermont Cancer Center, Department of Biochemistry, University of Vermont College of Medicine, 89 Beaumont Avenue, Burlington, VT 05405, USA
| | - A. Rasim Barutcu
- Department of Cell and Developmental Biology, University of Massachusetts Medical School, 55 Lake Avenue North, Worcester, MA 01655, USA
| | - Lori Martin-Buley
- University of Vermont Cancer Center, Department of Biochemistry, University of Vermont College of Medicine, 89 Beaumont Avenue, Burlington, VT 05405, USA
| | - André J. vanWijnen
- Departments of Orthopedic Surgery and Biochemistry & Molecular Biology, Mayo Clinic, Rochester, MN, USA
| | - Sayyed K. Zaidi
- University of Vermont Cancer Center, Department of Biochemistry, University of Vermont College of Medicine, 89 Beaumont Avenue, Burlington, VT 05405, USA
| | - Anthony N. Imbalzano
- Department of Cell and Developmental Biology, University of Massachusetts Medical School, 55 Lake Avenue North, Worcester, MA 01655, USA
| | - Jane B. Lian
- University of Vermont Cancer Center, Department of Biochemistry, University of Vermont College of Medicine, 89 Beaumont Avenue, Burlington, VT 05405, USA
| | - Janet L. Stein
- University of Vermont Cancer Center, Department of Biochemistry, University of Vermont College of Medicine, 89 Beaumont Avenue, Burlington, VT 05405, USA
| | - Gary S. Stein
- University of Vermont Cancer Center, Department of Biochemistry, University of Vermont College of Medicine, 89 Beaumont Avenue, Burlington, VT 05405, USA
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Pliss A, Fritz AJ, Stojkovic B, Ding H, Mukherjee L, Bhattacharya S, Xu J, Berezney R. Non-Random Patterns in the Distribution of NOR-Bearing Chromosome Territories in Human Fibroblasts: A Network Model of Interactions. J Cell Physiol 2015; 230:427-39. [PMID: 25077974 DOI: 10.1002/jcp.24726] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2014] [Accepted: 07/25/2014] [Indexed: 12/24/2022]
Abstract
We present a 3-D mapping in WI38 human diploid fibroblast cells of chromosome territories (CT) 13,14,15,21, and 22, which contain the nucleolar organizing regions (NOR) and participate in the formation of nucleoli. The nuclear radial positioning of NOR-CT correlated with the size of chromosomes with smaller CT more interior. A high frequency of pairwise associations between NOR-CT ranging from 52% (CT13-21) to 82% (CT15-21) was detected as well as a triplet arrangement of CT15-21-22 (72%). The associations of homologous CT were significantly lower (24-36%). Moreover, singular contacts between CT13-14 or CT13-22 were found in the majority of cells, while CT13-15 or CT13-21 predominantly exhibited multiple interactions. In cells with multiple nucleoli, one of the nucleoli (termed "dominant") always associated with a higher number of CT. Moreover, certain CT pairs more frequently contributed to the same nucleolus than to others. This nonrandom pattern suggests that a large number of the NOR-chromosomes are poised in close proximity during the postmitotic nucleolar recovery and through their NORs may contribute to the formation of the same nucleolus. A global data mining program termed the chromatic median determined the most probable interchromosomal arrangement of the entire NOR-CT population. This interactive network model was significantly above randomized simulation and was composed of 13 connections among the NOR-CT. We conclude that the NOR-CT form a global interactive network in the cell nucleus that may be a fundamental feature for the regulation of nucleolar and other genomic functions.
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Affiliation(s)
- Artem Pliss
- Department of Biological Sciences, University at Buffalo, State University of New York, Buffalo, New York
| | - Andrew J Fritz
- Department of Biological Sciences, University at Buffalo, State University of New York, Buffalo, New York
| | - Branislav Stojkovic
- Department of Computer Science and Engineering, University at Buffalo, State University of New York, Buffalo, New York
| | - Hu Ding
- Department of Computer Science and Engineering, University at Buffalo, State University of New York, Buffalo, New York
| | - Lopamudra Mukherjee
- Department of Computer Sciences, University at Wisconsin Whitewater, Whitewater, Wisconsin
| | - Sambit Bhattacharya
- Department of Computer Sciences, Fayetteville State University, Fayetteville, North Carolina
| | - Jinhui Xu
- Department of Computer Science and Engineering, University at Buffalo, State University of New York, Buffalo, New York
| | - Ronald Berezney
- Department of Biological Sciences, University at Buffalo, State University of New York, Buffalo, New York
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14
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Kupriyanova NS, Netchvolodov KK, Sadova AA, Cherepanova MD, Ryskov AP. Non-canonical ribosomal DNA segments in the human genome, and nucleoli functioning. Gene 2015; 572:237-42. [PMID: 26164756 DOI: 10.1016/j.gene.2015.07.019] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2015] [Revised: 06/16/2015] [Accepted: 07/07/2015] [Indexed: 10/23/2022]
Abstract
Ribosomal DNA (rDNA) in the human genome is represented by tandem repeats of 43 kb nucleotide sequences that form nucleoli organizers (NORs) on each of five pairs of acrocentric chromosomes. RDNA-similar segments of different lengths are also present on (NOR)(-) chromosomes. Many of these segments contain nucleotide substitutions, supplementary microsatellite clusters, and extended deletions. Recently, it was shown that, in addition to ribosome biogenesis, nucleoli exhibit additional functions, such as cell-cycle regulation and response to stresses. In particular, several stress-inducible loci located in the ribosomal intergenic spacer (rIGS) produce stimuli-specific noncoding nucleolus RNAs. By mapping the 5'/3' ends of the rIGS segments scattered throughout (NOR)(-) chromosomes, we discovered that the bonds in the rIGS that were most often susceptible to disruption in the rIGS were adjacent to, or overlapped with stimuli-specific inducible loci. This suggests the interconnection of the two phenomena - nucleoli functioning and the scattering of rDNA-like sequences on (NOR)(-) chromosomes.
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Affiliation(s)
| | | | - Anastasia A Sadova
- The Institute of Gene Biology, RAS, 34/5, Vavilov St., Moscow, Russian Federation.
| | - Marina D Cherepanova
- The Institute of Gene Biology, RAS, 34/5, Vavilov St., Moscow, Russian Federation.
| | - Alexei P Ryskov
- The Institute of Gene Biology, RAS, 34/5, Vavilov St., Moscow, Russian Federation.
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15
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Pérez-García C, Rouxel J, Akcha F. Development of a comet-FISH assay for the detection of DNA damage in hemocytes of Crassostrea gigas. AQUATIC TOXICOLOGY (AMSTERDAM, NETHERLANDS) 2015; 161:189-195. [PMID: 25710447 DOI: 10.1016/j.aquatox.2015.01.022] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/24/2014] [Revised: 01/14/2015] [Accepted: 01/25/2015] [Indexed: 06/04/2023]
Abstract
In this work, the DNA-damaging effect of hydrogen peroxide on the structural integrity of nucleolar organizer regions (NORs) was studied for the first time by comet-FISH in the Pacific oyster Crassostrea gigas. Global DNA damage was assessed in hemocytes using an alkaline version of the comet assay. Next, NOR sensitivity was analyzed by mapping major rDNA repeat unit by fluorescence in situ hybridization (FISH) on the same comet slides. Exposure of hemocytes to 100 μM of hydrogen peroxide induced a significant increase in both DNA damage and number of FISH-signals of major ribosomal genes versus the control. Moreover, a significant positive correlation was shown between DNA damage as measured by the comet assay (percentage of DNA in comet tail) and the number of signals present in comet tails. This study demonstrates the potential value of the comet-FISH assay for the study of DNA damage induced by genotoxicant exposure of target genes. It offers a perspective for better understanding the impact of genotoxicity on animal physiology and fitness.
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Affiliation(s)
- C Pérez-García
- IFREMER, Department of Biogeochemistry and Ecotoxicology, Laboratory of Ecotoxicology, Rue de l'Ile d'Yeu, BP 21105, 44311 Nantes Cedex 03, France.
| | - J Rouxel
- IFREMER, Department of Biogeochemistry and Ecotoxicology, Laboratory of Ecotoxicology, Rue de l'Ile d'Yeu, BP 21105, 44311 Nantes Cedex 03, France
| | - F Akcha
- IFREMER, Department of Biogeochemistry and Ecotoxicology, Laboratory of Ecotoxicology, Rue de l'Ile d'Yeu, BP 21105, 44311 Nantes Cedex 03, France.
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16
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Chromatin-Driven Behavior of Topologically Associating Domains. J Mol Biol 2015; 427:608-25. [DOI: 10.1016/j.jmb.2014.09.013] [Citation(s) in RCA: 82] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2014] [Revised: 09/17/2014] [Accepted: 09/23/2014] [Indexed: 12/19/2022]
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17
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Stępiński D. Functional ultrastructure of the plant nucleolus. PROTOPLASMA 2014; 251:1285-306. [PMID: 24756369 PMCID: PMC4209244 DOI: 10.1007/s00709-014-0648-6] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/18/2013] [Accepted: 04/08/2014] [Indexed: 05/23/2023]
Abstract
Nucleoli are nuclear domains present in almost all eukaryotic cells. They not only specialize in the production of ribosomal subunits but also play roles in many fundamental cellular activities. Concerning ribosome biosynthesis, particular stages of this process, i.e., ribosomal DNA transcription, primary RNA transcript processing, and ribosome assembly proceed in precisely defined nucleolar subdomains. Although eukaryotic nucleoli are conservative in respect of their main function, clear morphological differences between these structures can be noticed between individual kingdoms. In most cases, a plant nucleolus shows well-ordered structure in which four main ultrastructural components can be distinguished: fibrillar centers, dense fibrillar component, granular component, and nucleolar vacuoles. Nucleolar chromatin is an additional crucial structural component of this organelle. Nucleolonema, although it is not always an unequivocally distinguished nucleolar domain, has often been described as a well-grounded morphological element, especially of plant nucleoli. The ratios and morphology of particular subcompartments of a nucleolus can change depending on its metabolic activity which in turn is correlated with the physiological state of a cell, cell type, cell cycle phase, as well as with environmental influence. Precise attribution of functions to particular nucleolar subregions in the process of ribosome biosynthesis is now possible using various approaches. The presented description of plant nucleolar morphology summarizes previous knowledge regarding the function of nucleoli as well as of their particular subdomains not only in the course of ribosome biosynthesis.
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Affiliation(s)
- Dariusz Stępiński
- Department of Cytophysiology, Faculty of Biology and Environmental Protection, University of Łódź, Pomorska 141/143, 90-236, Łódź, Poland,
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Bočkor VV, Barišić D, Horvat T, Maglica Ž, Vojta A, Zoldoš V. Inhibition of DNA methylation alters chromatin organization, nuclear positioning and activity of 45S rDNA loci in cycling cells of Q. robur. PLoS One 2014; 9:e103954. [PMID: 25093501 PMCID: PMC4122370 DOI: 10.1371/journal.pone.0103954] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2014] [Accepted: 07/03/2014] [Indexed: 12/04/2022] Open
Abstract
Around 2200 copies of genes encoding ribosomal RNA (rRNA) in pedunculate oak, Quercus robur, are organized into two rDNA loci, the major (NOR-1) and the minor (NOR-2) locus. We present the first cytogenetic evidence indicating that the NOR-1 represents the active nucleolar organizer responsible for rRNA synthesis, while the NOR-2 probably stays transcriptionally silent and does not participate in the formation of the nucleolus in Q. robur, which is a situation resembling the well-known phenomenon of nucleolar dominance. rDNA chromatin topology analyses in cycling root tip cells by light and electron microscopy revealed the minor locus to be highly condensed and located away from the nucleolus, while the major locus was consistently associated with the nucleolus and often exhibited different levels of condensation. In addition, silver precipitation was confined exclusively to the NOR-1 locus. Also, NOR-2 was highly methylated at cytosines and rDNA chromatin was marked with histone modifications characteristic for repressive state. After treatment of the root cells with the methylation inhibitor 5-aza-2′-deoxycytidine, we observed an increase in the total level of rRNA transcripts and a decrease in DNA methylation level at the NOR-2 locus. Also, NOR-2 sites relocalized with respect to the nuclear periphery/nucleolus, however, the relocation did not affect the contribution of this locus to nucleolar formation, nor did it affect rDNA chromatin decondensation, strongly suggesting that NOR-2 has lost the function of rRNA synthesis and nucleolar organization.
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Affiliation(s)
- Vedrana Vičić Bočkor
- Faculty of Science, University of Zagreb, Department of Molecular Biology, Zagreb, Croatia
| | - Darko Barišić
- Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
| | - Tomislav Horvat
- Faculty of Science, University of Zagreb, Department of Molecular Biology, Zagreb, Croatia
| | - Željka Maglica
- Ecole Polytechnique Fédéral de Lausanne, Lausanne, Switzerland
| | - Aleksandar Vojta
- Faculty of Science, University of Zagreb, Department of Molecular Biology, Zagreb, Croatia
| | - Vlatka Zoldoš
- Faculty of Science, University of Zagreb, Department of Molecular Biology, Zagreb, Croatia
- * E-mail:
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19
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Mahboubi H, Stochaj U. Nucleoli and Stress Granules: Connecting Distant Relatives. Traffic 2014; 15:1179-93. [DOI: 10.1111/tra.12191] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2014] [Revised: 06/30/2014] [Accepted: 06/30/2014] [Indexed: 12/19/2022]
Affiliation(s)
- Hicham Mahboubi
- Department of Physiology; McGill University; 3655 Promenade Sir William Osler Montreal Quebec H3G 1Y6 Canada
| | - Ursula Stochaj
- Department of Physiology; McGill University; 3655 Promenade Sir William Osler Montreal Quebec H3G 1Y6 Canada
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20
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Booth DG, Takagi M, Sanchez-Pulido L, Petfalski E, Vargiu G, Samejima K, Imamoto N, Ponting CP, Tollervey D, Earnshaw WC, Vagnarelli P. Ki-67 is a PP1-interacting protein that organises the mitotic chromosome periphery. eLife 2014; 3:e01641. [PMID: 24867636 PMCID: PMC4032110 DOI: 10.7554/elife.01641] [Citation(s) in RCA: 127] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2013] [Accepted: 04/27/2014] [Indexed: 12/23/2022] Open
Abstract
When the nucleolus disassembles during open mitosis, many nucleolar proteins and RNAs associate with chromosomes, establishing a perichromosomal compartment coating the chromosome periphery. At present nothing is known about the function of this poorly characterised compartment. In this study, we report that the nucleolar protein Ki-67 is required for the assembly of the perichromosomal compartment in human cells. Ki-67 is a cell-cycle regulated protein phosphatase 1-binding protein that is involved in phospho-regulation of the nucleolar protein B23/nucleophosmin. Following siRNA depletion of Ki-67, NIFK, B23, nucleolin, and four novel chromosome periphery proteins all fail to associate with the periphery of human chromosomes. Correlative light and electron microscopy (CLEM) images suggest a near-complete loss of the entire perichromosomal compartment. Mitotic chromosome condensation and intrinsic structure appear normal in the absence of the perichromosomal compartment but significant differences in nucleolar reassembly and nuclear organisation are observed in post-mitotic cells.DOI: http://dx.doi.org/10.7554/eLife.01641.001.
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Affiliation(s)
- Daniel G Booth
- Wellcome Trust Centre for Cell Biology, University of Edinburgh, Edinburgh, United Kingdom
| | - Masatoshi Takagi
- Cellular Dynamics Laboratory, Riken Advanced Science Institute, Wako Saitama, Japan
| | - Luis Sanchez-Pulido
- MRC Functional Genomics Unit, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Elizabeth Petfalski
- Wellcome Trust Centre for Cell Biology, University of Edinburgh, Edinburgh, United Kingdom
| | - Giulia Vargiu
- Wellcome Trust Centre for Cell Biology, University of Edinburgh, Edinburgh, United Kingdom
| | - Kumiko Samejima
- Wellcome Trust Centre for Cell Biology, University of Edinburgh, Edinburgh, United Kingdom
| | - Naoko Imamoto
- Cellular Dynamics Laboratory, Riken Advanced Science Institute, Wako Saitama, Japan
| | - Chris P Ponting
- MRC Functional Genomics Unit, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - David Tollervey
- Wellcome Trust Centre for Cell Biology, University of Edinburgh, Edinburgh, United Kingdom
| | - William C Earnshaw
- Wellcome Trust Centre for Cell Biology, University of Edinburgh, Edinburgh, United Kingdom
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21
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Remodeling of three-dimensional organization of the nucleus during terminal keratinocyte differentiation in the epidermis. J Invest Dermatol 2013; 133:2191-201. [PMID: 23407401 DOI: 10.1038/jid.2013.66] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2012] [Revised: 12/19/2012] [Accepted: 01/09/2013] [Indexed: 01/01/2023]
Abstract
The nucleus of epidermal keratinocytes (KCs) is a complex and highly compartmentalized organelle, whose structure is markedly changed during terminal differentiation and transition of the genome from a transcriptionally active state seen in the basal and spinous epidermal cells to a fully inactive state in the keratinized cells of the cornified layer. Here, using multicolor confocal microscopy, followed by computational image analysis and mathematical modeling, we demonstrate that in normal mouse footpad epidermis, transition of KCs from basal epidermal layer to the granular layer is accompanied by marked differences in nuclear architecture and microenvironment including the following: (i) decrease in the nuclear volume; (ii) decrease in expression of the markers of transcriptionally active chromatin; (iii) internalization and decrease in the number of nucleoli; (iv) increase in the number of pericentromeric heterochromatic clusters; and (v) increase in the frequency of associations between the pericentromeric clusters, chromosomal territory 3, and nucleoli. These data suggest a role for nucleoli and pericentromeric heterochromatin clusters as organizers of nuclear microenvironment required for proper execution of gene expression programs in differentiating KCs, and provide important background information for further analyses of alterations in the topological genome organization seen in pathological skin conditions, including disorders of epidermal differentiation and epidermal tumors.
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Hiraga SI, Botsios S, Donze D, Donaldson AD. TFIIIC localizes budding yeast ETC sites to the nuclear periphery. Mol Biol Cell 2012; 23:2741-54. [PMID: 22496415 PMCID: PMC3395662 DOI: 10.1091/mbc.e11-04-0365] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Eukaryotic genomes contain multiple extra TFIIIC (ETC) sites that bind the TFIIIC transcription factor without recruiting RNA polymerase. TFIIIC directs the localization of Saccharomyces cerevisiae ETC sites to the nuclear periphery. Remarkably, however, perinuclear localization is not required for ETC sites to act as chromatin boundaries. Chromatin function requires specific three-dimensional architectures of chromosomes. We investigated whether Saccharomyces cerevisiae extra TFIIIC (ETC) sites, which bind the TFIIIC transcription factor but do not recruit RNA polymerase III, show specific intranuclear positioning. We show that six of the eight known S. cerevisiae ETC sites localize predominantly at the nuclear periphery, and that ETC sites retain their tethering function when moved to a new chromosomal location. Several lines of evidence indicate that TFIIIC is central to the ETC peripheral localization mechanism. Mutating or deleting the TFIIIC-binding consensus ablated ETC -site peripheral positioning, and inducing degradation of the TFIIIC subunit Tfc3 led to rapid release of an ETC site from the nuclear periphery. We find, moreover, that anchoring one TFIIIC subunit at an ectopic chromosomal site causes recruitment of others and drives peripheral tethering. Localization of ETC sites at the nuclear periphery also requires Mps3, a Sad1-UNC-84–domain protein that spans the inner nuclear membrane. Surprisingly, we find that the chromatin barrier and insulator functions of an ETC site do not depend on correct peripheral localization. In summary, TFIIIC and Mps3 together direct the intranuclear positioning of a new class of S. cerevisiae genomic loci positioned at the nuclear periphery.
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Affiliation(s)
- Shin-ichiro Hiraga
- Institute of Medical Sciences, University of Aberdeen, Aberdeen, Scotland, United Kingdom
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23
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Dimitrova DS. DNA replication initiation patterns and spatial dynamics of the human ribosomal RNA gene loci. J Cell Sci 2011; 124:2743-52. [DOI: 10.1242/jcs.082230] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Typically, only a fraction of the ≥600 ribosomal RNA (rRNA) gene copies in human cells are transcriptionally active. Expressed rRNA genes coalesce in specialized nuclear compartments – the nucleoli – and are believed to replicate during the first half of S phase. Paradoxically, attempts to visualize replicating rDNA during early S phase have failed. Here, I show that, in human (HeLa) cells, early-replicating rDNA is detectable at the nucleolar periphery and, more rarely, even outside nucleoli. Early-replicated rDNA relocates to the nucleolar interior and reassociates with the transcription factor UBF, implying that it predominantly represents expressed rDNA units. Contrary to the established model for active gene loci, replication initiates randomly throughout the early-replicating rDNA. By contrast, mostly silent rDNA copies replicate inside the nucleoli during mid and late S phase. At this stage, replication origins are fired preferentially within the non-transcribed intergenic spacers (NTSs), and ongoing rDNA transcription is required to maintain this specific initiation pattern. I propose that the unexpected spatial dynamics of the early-replicating rDNA repeats serve to ensure streamlined efficient replication of the most heavily transcribed genomic loci while simultaneously reducing the risk of chromosome breaks and rDNA hyper-recombination.
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24
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Abstract
Chromatin interactions, both in cis and trans and between transcriptionally active and silent regions, mean that the spatial organization of the genome is non-random. Spatial organization of the genome is non-random. Preferential chromatin interactions, both in cis and in trans and between transcriptionally active and silent regions, influence organization.
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Affiliation(s)
- Nathan F Cope
- Laboratory of Chromatin and Gene Expression, The Babraham Institute, Babraham Research Campus, Cambridge, UK
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25
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Royo F, Paz N, Espinosa L, McQueen PG, Vellón L, Parada LA. Spatial link between nucleoli and expression of the Zac1 gene. Chromosoma 2009; 118:711-22. [PMID: 19649645 DOI: 10.1007/s00412-009-0229-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2009] [Revised: 06/26/2009] [Accepted: 06/26/2009] [Indexed: 12/28/2022]
Abstract
Eukaryotic genomes are highly organized within the cell nucleus. Genome organization not only implies the preferential positioning of genetic elements in the interphase nucleus but also the topographic distribution of biological processes. We have investigated the relationship between spatial organization and genome function in single cells. Myc, c-Met, Igf2r, Asb4, and Zac1 genes have the same radial distribution, but they are not positioned in close proximity with respect to each other. Three-dimensional mapping of their transcription sites uncovered a gene-specific pattern of relative positioning with respect to the nucleolus. We found that the Zac1 gene transcription preferentially occurs juxtaposed to the nucleolus, and that its mRNA accumulates at this site of transcription. Nucleoli isolation followed by qRT-PCR provided evidence for a physical interaction between Zac1 mRNA and the nucleolus. Actinomycin-D treatment induced disassembly of the nucleolus, loss of the RNA-FISH signal, and dramatic increase of the ZAC protein level. However, inhibition of RNA polymerase II had no effect over the Zac1 FISH signal and the protein expression. Induction of cell cycle arrest, which involves participation of the ZAC protein, provoked mRNA release from its retention site and protein synthesis. Our data demonstrate that Zac1 mRNA preferentially accumulates in close proximity to nucleoli within the cell nucleus. In addition, our results suggest a functional link between such spatial distribution and protein expression.
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Affiliation(s)
- Félix Royo
- Cytogenomics, CIC bioGUNE-CIBEREHD, Par. Tec. Bizkaia Ed. 801 A, Derio, Spain
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26
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Stepiński D. Immunodetection of nucleolar proteins and ultrastructure of nucleoli of soybean root meristematic cells treated with chilling stress and after recovery. PROTOPLASMA 2009; 235:77-89. [PMID: 19241118 DOI: 10.1007/s00709-009-0033-z] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/23/2008] [Accepted: 01/19/2009] [Indexed: 05/03/2023]
Abstract
The nucleolar proteins, fibrillarin and nucleophosmin, have been identified immunofluorescently in the root meristematic cells of soybean seedlings under varying experimental conditions: at 25 degrees C (control), chilling at 10 degrees C for 3 h and 4 days and recovery from the chilling stress at 25 degrees C. In each experimental variant, the immunofluorescence signals were present solely at the nucleolar territories. Fluorescent staining for both proteins was mainly in the shape of circular domains that are assumed to correspond to the dense fibrillar component of the nucleoli. The fewest fluorescent domains were observed in the nucleoli of chilled plants, and the highest number was observed in the plants recovered after chilling. This difference in the number of circular domains in the nucleoli of each variant may indicate various levels of these proteins in each variant. Both the number of circular domains and the level of these nucleolar proteins changed with changes in the transcriptional activity of the nucleoli, with the more metabolically active cell having higher numbers of active areas in the nucleolus and higher levels of nucleolar proteins, and conversely. Electron microscopic studies revealed differences in the ultrastructure of the nucleoli in all experimental variants and confirmed that the number of fibrillar centres surrounded by dense fibrillar component was the lowest in the nucleoli of chilled plants, and the highest in the nucleoli of recovered seedlings.
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Affiliation(s)
- Dariusz Stepiński
- Department of Cytophysiology, University of Łódź, Pilarskiego 14, 90-231, Łódź, Poland.
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27
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Cvačková Z, Mašata M, Staněk D, Fidlerová H, Raška I. Chromatin position in human HepG2 cells: although being non-random, significantly changed in daughter cells. J Struct Biol 2009; 165:107-17. [PMID: 19056497 PMCID: PMC2658736 DOI: 10.1016/j.jsb.2008.10.007] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2008] [Revised: 10/24/2008] [Accepted: 10/27/2008] [Indexed: 12/22/2022]
Abstract
Mammalian chromosomes occupy chromosome territories within nuclear space the positions of which are generally accepted as non-random. However, it is still controversial whether position of chromosome territories/chromatin is maintained in daughter cells. We addressed this issue and investigated maintenance of various chromatin regions of unknown composition as well as nucleolus-associated chromatin, a significant part of which is composed of nucleolus organizer region-bearing chromosomes. The photoconvertible histone H4-Dendra2 was used to label such regions in transfected HepG2 cells, and its position was followed up to next interphase. The distribution of labeled chromatin in daughter cells exhibited a non-random character. However, its distribution in a vast majority of daughter cells extensively differed from the original ones and the labeled nucleolus-associated chromatin differently located into the vicinity of different nucleoli. Therefore, our results were not consistent with a concept of preservation chromatin position. This conclusion was supported by the finding that the numbers of nucleoli significantly differed between the two daughter cells. Our results support a view that while the transfected daughter HepG2 cells maintain some features of the parental cell chromosome organization, there is also a significant stochastic component associated with reassortment of chromosome territories/chromatin that results in their positional rearrangements.
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Affiliation(s)
| | | | | | | | - Ivan Raška
- Institute of Cellular Biology and Pathology, First Faculty of Medicine, Charles University in Prague, and Department of Cell Biology, Institute of Physiology, Academy of Sciences of the Czech Republic, v.v.i., Albertov 4, 128 00 Prague 2, Czech Republic
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28
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Chromatin: linking structure and function in the nucleolus. Chromosoma 2008; 118:11-23. [PMID: 18925405 DOI: 10.1007/s00412-008-0184-2] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2008] [Revised: 09/17/2008] [Accepted: 09/18/2008] [Indexed: 01/07/2023]
Abstract
The nucleolus is an informative model structure for studying how chromatin-regulated transcription relates to nuclear organisation. In this review, we describe how chromatin controls nucleolar structure through both the modulation of rDNA activity by convergently-evolved remodelling complexes and by direct effects upon rDNA packaging. This packaging not only regulates transcription but may also be important for suppressing internal recombination between tandem rDNA repeats. The identification of nucleolar histone chaperones and novel chromatin proteins by mass spectrometry suggests that structure-specific chromatin components remain to be characterised and may regulate the nucleolus in novel ways. However, it also suggests that there is considerable overlap between nucleolar and non-nucleolar-chromatin components. We conclude that a fuller understanding of nucleolar chromatin will be essential for understanding how gene organisation is linked with nuclear architecture.
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Kalmárová M, Smirnov E, Kováčik L, Popov A, Raska I. Positioning of the NOR-bearing chromosomes in relation to nucleoli in daughter cells after mitosis. Physiol Res 2008; 57:421-425. [PMID: 18597585 DOI: 10.33549/physiolres.931430] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
It is known that chromosomes occupy non-random positions in the cell nucleus. However, it is not clear to what extent their nuclear positions, together with their neighborhood, are conserved in daughter cells. To address specific aspects of this problem, we used the model of the chromosomes carrying ribosomal genes that are organized in clusters termed Nucleolus Organizer Regions (NORs). We compared the association of chosen NOR-bearing chromosomes (NOR-chromosomes) with nucleoli, as well as the numbers of nucleoli, in the pairs of daughter cells, and established how frequently the daughter cells had equal numbers of the homologs of certain NOR-chromosomes associated with individual nucleoli. The daughter cells typically had different numbers of nucleoli. At the same time, using immuno-FISH with probes for chromosomes 14 and 15 in HeLa cells, we found that the cell pairs with identical combinations appeared significantly more frequently than predicted by the random model. Thus, although the total number of chromosomes associated with nucleoli is variable, our data indicate that the position of the NOR-bearing chromosomes in relation to nucleoli is partly conserved through mitosis.
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Affiliation(s)
- M Kalmárová
- Institute of Cellular Biology and Pathology, First Faculty of Medicine, Charles University, Albertov 4, Prague 2, Czech Republic.
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30
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Tsai YT, Lin CI, Chen HK, Lee KM, Hsu CY, Yang SJ, Yeh NH. Chromatin tethering effects of hNopp140 are involved in the spatial organization of nucleolus and the rRNA gene transcription. J Biomed Sci 2008; 15:471-86. [PMID: 18253863 PMCID: PMC2440943 DOI: 10.1007/s11373-007-9226-7] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2007] [Accepted: 11/23/2007] [Indexed: 11/29/2022] Open
Abstract
The short arms of five human acrocentric chromosomes contain ribosomal gene (rDNA) clusters where numerous mini-nucleoli arise at the exit of mitosis. These small nucleoli tend to coalesce into one or a few large nucleoli during interphase by unknown mechanisms. Here, we demonstrate that the N- and C-terminal domains of a nucleolar protein, hNopp140, bound respectively to alpha-satellite arrays and rDNA clusters of acrocentric chromosomes for nucleolar formation. The central acidic-and-basic repeated domain of hNopp140, possessing a weak self-self interacting ability, was indispensable for hNopp140 to build up a nucleolar round-shaped structure. The N- or the C-terminally truncated hNopp140 caused nucleolar segregation and was able to alter locations of the rDNA transcription, as mediated by detaching the rDNA repeats from the acrocentric alpha-satellite arrays. Interestingly, an hNopp140 mutant, made by joining the N- and C-terminal domains but excluding the entire central repeated region, induced nucleolar disruption and global chromatin condensation. Furthermore, RNAi knockdown of hNopp140 resulted in dispersion of the rDNA and acrocentric alpha-satellite sequences away from nucleolus that was accompanied by rDNA transcriptional silence. Our findings indicate that hNopp140, a scaffold protein, is involved in the nucleolar assembly, fusion, and maintenance.
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Affiliation(s)
- Yi-Tzang Tsai
- School of Life Science, Institute of Microbiology and Immunology, National Yang-Ming University, 155 Li-Nong Street Sec. 2, Taipei, 112, Taiwan
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