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Penagos-Puig A, Claudio-Galeana S, Stephenson-Gussinye A, Jácome-López K, Aguilar-Lomas A, Chen X, Pérez-Molina R, Furlan-Magaril M. RNA polymerase II pausing regulates chromatin organization in erythrocytes. Nat Struct Mol Biol 2023; 30:1092-1104. [PMID: 37500929 DOI: 10.1038/s41594-023-01037-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2022] [Accepted: 06/16/2023] [Indexed: 07/29/2023]
Abstract
Chicken erythrocytes are nucleated cells often considered to be transcriptionally inactive, although the epigenetic changes and chromatin remodeling that would mediate transcriptional repression and the extent of gene silencing during avian terminal erythroid differentiation are not fully understood. Here, we characterize the changes in gene expression, chromatin accessibility, genome organization and chromatin nuclear disposition during the terminal stages of erythropoiesis in chicken and uncover complex chromatin reorganization at different genomic scales. We observe a robust decrease in transcription in erythrocytes, but a set of genes maintains their expression, including genes involved in RNA polymerase II (Pol II) promoter-proximal pausing. Erythrocytes exhibit a reoriented nuclear architecture, with accessible chromatin positioned towards the nuclear periphery together with the paused RNA Pol II. In erythrocytes, chromatin domains are partially lost genome-wide, except at minidomains retained around paused promoters. Our results suggest that promoter-proximal pausing of RNA Pol II contributes to the transcriptional regulation of the erythroid genome and highlight the role of RNA polymerase in the maintenance of local chromatin organization.
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Affiliation(s)
- Andrés Penagos-Puig
- Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City, Mexico
| | - Sherlyn Claudio-Galeana
- Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City, Mexico
| | - Aura Stephenson-Gussinye
- Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City, Mexico
| | - Karina Jácome-López
- Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City, Mexico
| | - Amaury Aguilar-Lomas
- Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City, Mexico
| | - Xingqi Chen
- Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden
| | - Rosario Pérez-Molina
- Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City, Mexico
| | - Mayra Furlan-Magaril
- Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City, Mexico.
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Hao F, Mishra LN, Jaya P, Jones R, Hayes JJ. Identification and Analysis of Six Phosphorylation Sites Within the Xenopus laevis Linker Histone H1.0 C-Terminal Domain Indicate Distinct Effects on Nucleosome Structure. Mol Cell Proteomics 2022; 21:100250. [PMID: 35618225 PMCID: PMC9243160 DOI: 10.1016/j.mcpro.2022.100250] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2021] [Revised: 05/01/2022] [Accepted: 05/20/2022] [Indexed: 11/25/2022] Open
Abstract
As a key structural component of the chromatin of higher eukaryotes, linker histones (H1s) are involved in stabilizing the folding of extended nucleosome arrays into higher-order chromatin structures and function as a gene-specific regulator of transcription in vivo. The H1 C-terminal domain (CTD) is essential for high-affinity binding of linker histones to chromatin and stabilization of higher-order chromatin structure. Importantly, the H1 CTD is an intrinsically disordered domain that undergoes a drastic condensation upon binding to nucleosomes. Moreover, although phosphorylation is a prevalent post-translational modification within the H1 CTD, exactly where this modification is installed and how phosphorylation influences the structure of the H1 CTD remains unclear for many H1s. Using novel mass spectrometry techniques, we identified six phosphorylation sites within the CTD of the archetypal linker histone Xenopus H1.0. We then analyzed nucleosome-dependent CTD condensation and H1-dependent linker DNA organization for H1.0 in which the phosphorylated serine residues were replaced by glutamic acid residues (phosphomimics) in six independent mutants. We find that phosphomimetics at residues S117E, S155E, S181E, S188E, and S192E resulted in a significant reduction in nucleosome-bound H1.0 CTD condensation compared with unphosphorylated H1.0, whereas S130E did not alter CTD structure. Furthermore, we found distinct effects among the phosphomimetics on H1-dependent linker DNA trajectory, indicating unique mechanisms by which this modification can influence H1 CTD condensation. These results bring to light a novel role for linker histone phosphorylation in directly altering the structure of nucleosome-bound H1 and a potential novel mechanism for its effects on chromatin structure and function.
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Affiliation(s)
- Fanfan Hao
- Department of Biochemistry and Biophysics, University of Rochester Medical Center, Rochester, New York, USA
| | - Laxmi N Mishra
- Department of Biochemistry and Biophysics, University of Rochester Medical Center, Rochester, New York, USA
| | - Prasoon Jaya
- Department of Biochemistry and Biophysics, University of Rochester Medical Center, Rochester, New York, USA; Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, Bronx, New York, USA
| | | | - Jeffrey J Hayes
- Department of Biochemistry and Biophysics, University of Rochester Medical Center, Rochester, New York, USA.
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Histone H1 Post-Translational Modifications: Update and Future Perspectives. Int J Mol Sci 2020; 21:ijms21165941. [PMID: 32824860 PMCID: PMC7460583 DOI: 10.3390/ijms21165941] [Citation(s) in RCA: 41] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2020] [Revised: 08/07/2020] [Accepted: 08/08/2020] [Indexed: 12/12/2022] Open
Abstract
Histone H1 is the most variable histone and its role at the epigenetic level is less characterized than that of core histones. In vertebrates, H1 is a multigene family, which can encode up to 11 subtypes. The H1 subtype composition is different among cell types during the cell cycle and differentiation. Mass spectrometry-based proteomics has added a new layer of complexity with the identification of a large number of post-translational modifications (PTMs) in H1. In this review, we summarize histone H1 PTMs from lower eukaryotes to humans, with a particular focus on mammalian PTMs. Special emphasis is made on PTMs, whose molecular function has been described. Post-translational modifications in H1 have been associated with the regulation of chromatin structure during the cell cycle as well as transcriptional activation, DNA damage response, and cellular differentiation. Additionally, PTMs in histone H1 that have been linked to diseases such as cancer, autoimmune disorders, and viral infection are examined. Future perspectives and challenges in the profiling of histone H1 PTMs are also discussed.
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Kowalski A, Pałyga J. Modulation of chromatin function through linker histone H1 variants. Biol Cell 2016; 108:339-356. [PMID: 27412812 DOI: 10.1111/boc.201600007] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2016] [Revised: 07/08/2016] [Accepted: 07/08/2016] [Indexed: 12/30/2022]
Abstract
In this review, the structural aspects of linker H1 histones are presented as a background for characterization of the factors influencing their function in animal and human chromatin. The action of H1 histone variants is largely determined by dynamic alterations of their intrinsically disordered tail domains, posttranslational modifications and allelic diversification. The interdependent effects of these factors can establish dynamic histone H1 states that may affect the organization and function of chromatin regions.
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Affiliation(s)
- Andrzej Kowalski
- Department of Biochemistry and Genetics, Institute of Biology, Jan Kochanowski University, 25-406 Kielce, Poland
| | - Jan Pałyga
- Department of Biochemistry and Genetics, Institute of Biology, Jan Kochanowski University, 25-406 Kielce, Poland
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5
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Lopez R, Sarg B, Lindner H, Bartolomé S, Ponte I, Suau P, Roque A. Linker histone partial phosphorylation: effects on secondary structure and chromatin condensation. Nucleic Acids Res 2015; 43:4463-76. [PMID: 25870416 PMCID: PMC4482070 DOI: 10.1093/nar/gkv304] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2014] [Accepted: 03/27/2015] [Indexed: 11/29/2022] Open
Abstract
Linker histones are involved in chromatin higher-order structure and gene regulation. We have successfully achieved partial phosphorylation of linker histones in chicken erythrocyte soluble chromatin with CDK2, as indicated by HPCE, MALDI-TOF and Tandem MS. We have studied the effects of linker histone partial phosphorylation on secondary structure and chromatin condensation. Infrared spectroscopy analysis showed a gradual increase of β-structure in the phosphorylated samples, concomitant to a decrease in α-helix/turns, with increasing linker histone phosphorylation. This conformational change could act as the first step in the phosphorylation-induced effects on chromatin condensation. A decrease of the sedimentation rate through sucrose gradients of the phosphorylated samples was observed, indicating a global relaxation of the 30-nm fiber following linker histone phosphorylation. Analysis of specific genes, combining nuclease digestion and qPCR, showed that phosphorylated samples were more accessible than unphosphorylated samples, suggesting local chromatin relaxation. Chromatin aggregation was induced by MgCl2 and analyzed by dynamic light scattering (DLS). Phosphorylated chromatin had lower percentages in volume of aggregated molecules and the aggregates had smaller hydrodynamic diameter than unphosphorylated chromatin, indicating that linker histone phosphorylation impaired chromatin aggregation. These findings provide new insights into the effects of linker histone phosphorylation in chromatin condensation.
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Affiliation(s)
- Rita Lopez
- Departamento de Bioquímica y Biología Molecular, Facultad de Biociencias, Universidad Autónoma de Barcelona, 08193, Bellaterra, Barcelona, Spain
| | - Bettina Sarg
- Division of Clinical Biochemistry, Biocenter, Innsbruck Medical University, A-6020, Innsbruck, Austria
| | - Herbert Lindner
- Division of Clinical Biochemistry, Biocenter, Innsbruck Medical University, A-6020, Innsbruck, Austria
| | - Salvador Bartolomé
- Laboratorio de Luminiscencia y Espectroscopia de Biomoléculas, Universidad Autónoma de Barcelona, 08193, Bellaterra, Barcelona, Spain
| | - Inma Ponte
- Departamento de Bioquímica y Biología Molecular, Facultad de Biociencias, Universidad Autónoma de Barcelona, 08193, Bellaterra, Barcelona, Spain
| | - Pedro Suau
- Departamento de Bioquímica y Biología Molecular, Facultad de Biociencias, Universidad Autónoma de Barcelona, 08193, Bellaterra, Barcelona, Spain
| | - Alicia Roque
- Departamento de Bioquímica y Biología Molecular, Facultad de Biociencias, Universidad Autónoma de Barcelona, 08193, Bellaterra, Barcelona, Spain
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Raphael S, Mélissa PL, Aurélien B, Emmanuelle V, Marc PJ, Sylvie B, Alain D, Wilfried S. Kinetic response of a genotoxicity biomarker in the three-spined stickleback and implication for environmental monitoring. ECOTOXICOLOGY AND ENVIRONMENTAL SAFETY 2014; 102:6-11. [PMID: 24580815 DOI: 10.1016/j.ecoenv.2014.01.006] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/17/2013] [Revised: 01/08/2014] [Accepted: 01/08/2014] [Indexed: 06/03/2023]
Abstract
The ultimate sink for the majority of anthropogenic compounds are the aquatic ecosystems, either through direct discharges or indirectly through hydrologic or atmospheric processes, possibly leading to long-term adverse effects in aquatic living resources. In order to assess exposure, fate and effects of chemical contaminants, aquatic ecotoxicologists have developed a large array of early-warning biomarkers proving that toxicants have entered organisms, have been distributed between organs and have triggered toxic effects regarding critical targets. However, optimal use of biomarkers in environmental studies previously requires in-depth knowledge of the kinetics of response of biomarkers. This work aimed to define as a first step of a validation process the kinetic response of a genotoxicity biomarker recently developed in the three-spined stickleback (Gasterosteus aculeatus). DNA damage was assessed in stickleback erythrocytes after in vivo exposure for 12 days to methylmethanesulfonate (MMS), an alkylating compound, followed by a 20 day-recovery period. Results show a dose-response relationship, time to maximal induction being reached after 6 days at the highest MMS concentration. No acclimation process was noticed during exposure whatever the MMS concentration, and genotoxicity decreased during the recovery phase only in fish exposed to the highest MMS concentration, suggesting more an effect of erythrocyte turn-over than of DNA repair system on the observed DNA damage level. Further field experiments are needed before including this genotoxicity biomarker in a battery of biochemical markers to monitor adverse effects of pollutants on fish health.
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Affiliation(s)
- Santos Raphael
- Institut National de l'Environnement Industriel et des Risques (INERIS), Unité d'écotoxicologie in vitro et in vivo, BP 2, F-60550 Verneuil en Halatte, France; Université de Lyon, UMR 5023 LEHNA, F-69100, Villeurbanne, France
| | - Palos-Ladeiro Mélissa
- Institut National de l'Environnement Industriel et des Risques (INERIS), Unité d'écotoxicologie in vitro et in vivo, BP 2, F-60550 Verneuil en Halatte, France
| | - Besnard Aurélien
- Centre d'Ecologie Fonctionnelle et Evolutive (UMR 5175), Ecole Pratique des Hautes Etudes, Biogéographie et Ecologie des Vertébrés, Campus CNRS, 1919 Route de Mende, 34 293 Montpellier Cedex 5, France
| | - Vulliet Emmanuelle
- Institut des Sciences Analytiques, Département Service Central d'Analyse, UMR 5280, 5 rue de la Doua, F-69100, Villeurbanne, France
| | - Porcher Jean Marc
- Institut National de l'Environnement Industriel et des Risques (INERIS), Unité d'écotoxicologie in vitro et in vivo, BP 2, F-60550 Verneuil en Halatte, France
| | - Bony Sylvie
- Université de Lyon, UMR 5023 LEHNA, F-69100, Villeurbanne, France; INRA, USC IGH 1369, ENTPE, F-69518, Vaulx en Velin, France
| | - Devaux Alain
- Université de Lyon, UMR 5023 LEHNA, F-69100, Villeurbanne, France; INRA, USC IGH 1369, ENTPE, F-69518, Vaulx en Velin, France
| | - Sanchez Wilfried
- Institut National de l'Environnement Industriel et des Risques (INERIS), Unité d'écotoxicologie in vitro et in vivo, BP 2, F-60550 Verneuil en Halatte, France.
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Kostova NN, Srebreva L, Markov DV, Sarg B, Lindner HH, Rundquist I. Histone H5-chromatin interactions in situ are strongly modulated by H5 C-terminal phosphorylation. Cytometry A 2012; 83:273-9. [DOI: 10.1002/cyto.a.22221] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2012] [Revised: 09/21/2012] [Accepted: 09/22/2012] [Indexed: 12/23/2022]
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Öberg C, Izzo A, Schneider R, Wrange Ö, Belikov S. Linker Histone Subtypes Differ in Their Effect on Nucleosomal Spacing In Vivo. J Mol Biol 2012; 419:183-97. [DOI: 10.1016/j.jmb.2012.03.007] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2011] [Revised: 02/17/2012] [Accepted: 03/12/2012] [Indexed: 10/28/2022]
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9
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Kowalski A, Pałyga J. Chromatin compaction in terminally differentiated avian blood cells: the role of linker histone H5 and non-histone protein MENT. Chromosome Res 2011; 19:579-90. [PMID: 21656257 PMCID: PMC3139888 DOI: 10.1007/s10577-011-9218-3] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2011] [Revised: 05/04/2011] [Accepted: 05/06/2011] [Indexed: 10/28/2022]
Abstract
Chromatin has a tendency to shift from a relatively decondensed (active) to condensed (inactive) state during cell differentiation due to interactions of specific architectural and/or regulatory proteins with DNA. A promotion of chromatin folding in terminally differentiated avian blood cells requires the presence of either histone H5 in erythrocytes or non-histone protein, myeloid and erythroid nuclear termination stage-specific protein (MENT), in white blood cells (lymphocytes and granulocytes). These highly abundant proteins assist in folding of nucleosome arrays and self-association of chromatin fibers into compacted chromatin structures. Here, we briefly review structural aspects and molecular mode of action by which these unrelated proteins can spread condensed chromatin to form inactivated regions in the genome.
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Affiliation(s)
- Andrzej Kowalski
- Department of Biochemistry and Genetics, Institute of Biology, Jan Kochanowski University, ul. Świętokrzyska 15, 25-406 Kielce, Poland.
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10
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Popova EY, Krauss SW, Short SA, Lee G, Villalobos J, Etzell J, Koury MJ, Ney PA, Chasis JA, Grigoryev SA. Chromatin condensation in terminally differentiating mouse erythroblasts does not involve special architectural proteins but depends on histone deacetylation. Chromosome Res 2009; 17:47-64. [PMID: 19172406 DOI: 10.1007/s10577-008-9005-y] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2008] [Revised: 10/13/2008] [Accepted: 10/13/2008] [Indexed: 01/09/2023]
Abstract
Terminal erythroid differentiation in vertebrates is characterized by progressive heterochromatin formation and chromatin condensation and, in mammals, culminates in nuclear extrusion. To date, although mechanisms regulating avian erythroid chromatin condensation have been identified, little is known regarding this process during mammalian erythropoiesis. To elucidate the molecular basis for mammalian erythroblast chromatin condensation, we used Friend virus-infected murine spleen erythroblasts that undergo terminal differentiation in vitro. Chromatin isolated from early and late-stage erythroblasts had similar levels of linker and core histones, only a slight difference in nucleosome repeats, and no significant accumulation of known developmentally regulated architectural chromatin proteins. However, histone H3(K9) dimethylation markedly increased while histone H4(K12) acetylation dramatically decreased and became segregated from the histone methylation as chromatin condensed. One histone deacetylase, HDAC5, was significantly upregulated during the terminal stages of Friend virus-infected erythroblast differentiation. Treatment with histone deacetylase inhibitor, trichostatin A, blocked both chromatin condensation and nuclear extrusion. Based on our data, we propose a model for a unique mechanism in which extensive histone deacetylation at pericentromeric heterochromatin mediates heterochromatin condensation in vertebrate erythroblasts that would otherwise be mediated by developmentally-regulated architectural proteins in nucleated blood cells.
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Affiliation(s)
- Evgenya Y Popova
- Biochemistry and Molecular Biology, College of Medicine, Penn State University, Hershey, PA 17033, USA
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12
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Rundquist I, Lindner HH. Analyses of linker histone--chromatin interactions in situ. Biochem Cell Biol 2007; 84:427-36. [PMID: 16936816 DOI: 10.1139/o06-071] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Recent studies, using cytometric techniques based on fluorescence microscopy, have provided new information on how linker histones interact with chromatin in vivo or in situ. In particular, the use of green fluorescent proteins (GFPs) has enabled detailed studies of how individual H1 subtypes, and specific motifs in them, interact with chromatin in vivo. Furthermore, the development of cytochemical methods to study the interaction between linker histones and chromatin using DNA-binding fluorochromes as indirect probes for linker histone affinity in situ, in combination with highly sensitive and specific analytical methods, has provided additional information on the interactions between linker histones and chromatin in several cell systems. Such results verified that linker histones have a substantially higher affinity for chromatin in mature chicken erythrocytes than in frog erythrocytes, and they also indicated that the affinity decreased during differentiation of the frog erythrocytes. Furthermore, in cultured human fibroblasts, the linker histones showed a relatively high affinity for chromatin in interphase, whereas it showed a significantly lower affinity in highly condensed metaphase chromosomes. This method also enables the analysis of linker histone affinity for chromatin in H1-depleted fibroblasts reconstituted with purified linker histones. No consistent correlation between linker histone affinity and chromatin condensation has so far been detected.
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Affiliation(s)
- Ingemar Rundquist
- Department of Biomedicine and Surgery, Division of Cell Biology, Faculty of Health Sciences, Linköpings universitet, SE-58185 Linköping, Sweden.
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Gilbert N, Boyle S, Sutherland H, de Las Heras J, Allan J, Jenuwein T, Bickmore WA. Formation of facultative heterochromatin in the absence of HP1. EMBO J 2004; 22:5540-50. [PMID: 14532126 PMCID: PMC213774 DOI: 10.1093/emboj/cdg520] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Facultative heterochromatin is a cytological manifestation of epigenetic mechanisms that regulate gene expression. Constitutive heterochromatin is marked by distinctive histone H3 methylation and the presence of HP1 proteins, but the chromatin modifications of facultative heterochromatin are less clear. We have examined histone modifications and HP1 in the facultative heterochromatin of nucleated erythrocytes and show that mouse and chicken erythrocytes have different mechanisms of heterochromatin formation. Mouse embryonic erythrocytes have abundant HP1, increased tri-methylation of H3 at K9 and loss of H3 tri-methylation at K27. In contrast, we show that HP1 proteins are lost during the differentiation of chicken erythrocytes, and that H3 tri-methylation at both K9 and K27 is reduced. This coincides with the appearance of the variant linker histone H5. HP1s are also absent from erythrocytes of Xenopus and zebrafish. Our data show that in the same cell lineage there are different mechanisms for forming facultative heterochromatin in vertebrates. To our knowledge, this is the first report of cell types that lack HP1s and that have gross changes in the levels of histone modifications.
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Affiliation(s)
- Nick Gilbert
- MRC Human Genetics Unit, Crewe Road, Edinburgh EH4 2XU, UK
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Kostova NN, Srebreva L, Markov DV, Rundquist I. Histone H1 and chromatin interactions in human fibroblast nuclei after H1 depletion and reconstitution with H1 subfractions. ACTA ACUST UNITED AC 2004; 58:132-9. [PMID: 15057966 DOI: 10.1002/cyto.a.10119] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
BACKGROUND Linker histones constitute a family of lysine-rich proteins associated with nucleosome core particles and linker DNA in eukaryotic chromatin. In permeabilized cells, they can be extracted from nuclei by using salt concentration in the range of 0.3 to 0.7 M. Although other nuclear proteins are also extracted at 0.7 M salt, the remaining nucleus represents a template that is relatively intact. METHODS A cytochemical method was used to study the affinity of reconstituted linker histones for chromatin in situ in cultured human fibroblasts. We also investigated their ability to condense chromatin by using DNA-specific osmium ammine staining for electron microscopy. RESULTS Permeabilized and H1-depleted fibroblast nuclei were suitable for the study of linker histone-chromatin interactions after reconstitution with purified linker histone subfractions. Our results showed that exogenous linker histones bind to chromatin with lower affinity than the native ones. We detected no significant differences between the main H1 and H1 degrees histone fractions with respect to their affinity for chromatin or in their ability to condense chromatin. CONCLUSIONS Linker histone interactions with chromatin are controlled also by mechanisms independent of linker histone subtype composition.
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Affiliation(s)
- Nora N Kostova
- Institute of Molecular Biology, Bulgarian Academy of Sciences, Sofia, Bulgaria
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