γh2ax foci form preferentially in euchromatin after ionising-radiation电离辐射后γh2ax焦点形式优先常染色质.pdfVIP

cH2AX Foci Form Preferentially in Euchromatin after Ionising-Radiation 1 1 2 1 3 3 Ian G. Cowell *, Nicola J. Sunter , Prim B. Singh , Caroline A. Austin , Barbara W. Durkacz , Michael J. Tilby 1 Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle upon Tyne, United Kingdom, 2 Division of Tumour Biology, Forschungszentrum Borstel, Borstel, Germany, 3 Northern Institute for Cancer Research, Newcastle University, Newcastle upon Tyne, United Kingdom 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 cH2AX 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 cH2AX 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