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γH2AX Foci Form Preferentially in Euchromatin after Ionising-Radiation

BACKGROUND: The histone variant histone H2A.X comprises up to 25% of the H2A complement in mammalian cells. It is rapidly phosphorylated following exposure of cells to double-strand break (DSB) inducing agents such as ionising radiation. Within minutes of DSB generation, H2AX molecules are phosphory...

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Autores principales: Cowell, Ian G., Sunter, Nicola J., Singh, Prim B., Austin, Caroline A., Durkacz, Barbara W., Tilby, Michael J.
Formato: Texto
Lenguaje:English
Publicado: Public Library of Science 2007
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2020439/
https://www.ncbi.nlm.nih.gov/pubmed/17957241
http://dx.doi.org/10.1371/journal.pone.0001057
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author Cowell, Ian G.
Sunter, Nicola J.
Singh, Prim B.
Austin, Caroline A.
Durkacz, Barbara W.
Tilby, Michael J.
author_facet Cowell, Ian G.
Sunter, Nicola J.
Singh, Prim B.
Austin, Caroline A.
Durkacz, Barbara W.
Tilby, Michael J.
author_sort Cowell, Ian G.
collection PubMed
description BACKGROUND: The histone variant histone H2A.X comprises up to 25% of the H2A complement in mammalian cells. It is rapidly phosphorylated following exposure of cells to double-strand break (DSB) inducing agents such as ionising radiation. Within minutes of DSB generation, H2AX molecules are phosphorylated in large chromatin domains flanking DNA double-strand breaks (DSBs); these domains can be observed by immunofluorescence microscopy and are termed γH2AX foci. H2AX phosphorylation is believed to have a role mounting an efficient cellular response to DNA damage. Theoretical considerations suggest an essentially random chromosomal distribution of X-ray induced DSBs, and experimental evidence does not consistently indicate otherwise. However, we observed an apparently uneven distribution of γH2AX foci following X-irradiation with regions of the nucleus devoid of foci. METHODOLOGY/PRINCIPLE FINDINGS: Using immunofluorescence microscopy, we show that focal phosphorylation of histone H2AX occurs preferentially in euchromatic regions of the genome following X-irradiation. H2AX phosphorylation has also been demonstrated previously to occur at stalled replication forks induced by UV radiation or exposure to agents such as hydroxyurea. In this study, treatment of S-phase cells with hydroxyurea lead to efficient H2AX phosphorylation in both euchromatin and heterochromatin at times when these chromatin compartments were undergoing replication. This suggests a block to H2AX phosphorylation in heterochromatin that is at least partially relieved by ongoing DNA replication. CONCLUSIONS/SIGNIFICANCE: We discus a number of possible mechanisms that could account for the observed pattern of H2AX phosphorylation. Since γH2AX is regarded as forming a platform for the recruitment or retention of other DNA repair and signaling molecules, these findings imply that the processing of DSBs in heterochromatin differs from that in euchromatic regions. The differential responses of heterochromatic and euchromatic compartments of the genome to DSBs will have implications for understanding the processes of DNA repair in relation to nuclear and chromatin organization.
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spelling pubmed-20204392007-10-24 γH2AX Foci Form Preferentially in Euchromatin after Ionising-Radiation Cowell, Ian G. Sunter, Nicola J. Singh, Prim B. Austin, Caroline A. Durkacz, Barbara W. Tilby, Michael J. PLoS One Research Article BACKGROUND: The histone variant histone H2A.X comprises up to 25% of the H2A complement in mammalian cells. It is rapidly phosphorylated following exposure of cells to double-strand break (DSB) inducing agents such as ionising radiation. Within minutes of DSB generation, H2AX molecules are phosphorylated in large chromatin domains flanking DNA double-strand breaks (DSBs); these domains can be observed by immunofluorescence microscopy and are termed γH2AX foci. H2AX phosphorylation is believed to have a role mounting an efficient cellular response to DNA damage. Theoretical considerations suggest an essentially random chromosomal distribution of X-ray induced DSBs, and experimental evidence does not consistently indicate otherwise. However, we observed an apparently uneven distribution of γH2AX foci following X-irradiation with regions of the nucleus devoid of foci. METHODOLOGY/PRINCIPLE FINDINGS: Using immunofluorescence microscopy, we show that focal phosphorylation of histone H2AX occurs preferentially in euchromatic regions of the genome following X-irradiation. H2AX phosphorylation has also been demonstrated previously to occur at stalled replication forks induced by UV radiation or exposure to agents such as hydroxyurea. In this study, treatment of S-phase cells with hydroxyurea lead to efficient H2AX phosphorylation in both euchromatin and heterochromatin at times when these chromatin compartments were undergoing replication. This suggests a block to H2AX phosphorylation in heterochromatin that is at least partially relieved by ongoing DNA replication. CONCLUSIONS/SIGNIFICANCE: We discus a number of possible mechanisms that could account for the observed pattern of H2AX phosphorylation. Since γH2AX is regarded as forming a platform for the recruitment or retention of other DNA repair and signaling molecules, these findings imply that the processing of DSBs in heterochromatin differs from that in euchromatic regions. The differential responses of heterochromatic and euchromatic compartments of the genome to DSBs will have implications for understanding the processes of DNA repair in relation to nuclear and chromatin organization. Public Library of Science 2007-10-24 /pmc/articles/PMC2020439/ /pubmed/17957241 http://dx.doi.org/10.1371/journal.pone.0001057 Text en Cowell et al. http://creativecommons.org/licenses/by/4.0/ This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are properly credited.
spellingShingle Research Article
Cowell, Ian G.
Sunter, Nicola J.
Singh, Prim B.
Austin, Caroline A.
Durkacz, Barbara W.
Tilby, Michael J.
γH2AX Foci Form Preferentially in Euchromatin after Ionising-Radiation
title γH2AX Foci Form Preferentially in Euchromatin after Ionising-Radiation
title_full γH2AX Foci Form Preferentially in Euchromatin after Ionising-Radiation
title_fullStr γH2AX Foci Form Preferentially in Euchromatin after Ionising-Radiation
title_full_unstemmed γH2AX Foci Form Preferentially in Euchromatin after Ionising-Radiation
title_short γH2AX Foci Form Preferentially in Euchromatin after Ionising-Radiation
title_sort γh2ax foci form preferentially in euchromatin after ionising-radiation
topic Research Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2020439/
https://www.ncbi.nlm.nih.gov/pubmed/17957241
http://dx.doi.org/10.1371/journal.pone.0001057
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