title: Species conserved DNA damage response at the inactive human X chromosome.
abstract: Chromatin modifications are long known as an essential part of the orchestrated response resulting in the repair of radiation-induced DNA double-strand breaks (DSBs). Only recently, however, the influence of the chromatin architecture itself on the DNA damage response has been recognised. Thus for heterochromatic DSBs the sensing and early recruitment of repair factors to the lesion occurs within the heterochromatic compartments, but the damage sites are subsequently relocated from the inside to the outside of the heterochromatin. While previous studies were accomplished at the constitutive heterochromatin of centromeric regions in mouse and flies, here we examine the DSB repair at the facultative heterochromatin of the inactive X chromosome (Xi) in humans. Using heavy ion irradiation we show that at later times after irradiation the DSB damage streaks bend around the Xi verifying that the relocation process is conserved between species and not specialised to repetitive sequences only. In addition, to measure chromatin relaxation at rare positions within the genome, we established live cell microscopy at the GSI microbeam thus allowing the aimed irradiation of small nuclear structures like the Xi. Chromatin decondensation at DSBs within the Xi is clearly visible within minutes as a continuous decrease of the DNA staining over time, comparable to the DNA relaxation revealed at DSBs in mouse chromocenters. Furthermore, despite being conserved between species, slight differences in the underlying regulation of these processes in heterochromatic DSBs are apparent.
authors.affiliation: GSI Helmholtzzentrum für Schwerionenforschung, Planckstraße 1, 64291 Darmstadt, Germany. Electronic address: I.Mueller@gsi.de.
authors.forename: Iris
authors.initials: I
authors.lastname: Müller
authors.forename: Bruno
authors.initials: B
authors.lastname: Merk
authors.forename: Kay-Obbe
authors.initials: KO
authors.lastname: Voss
authors.forename: Nicole
authors.initials: N
authors.lastname: Averbeck
authors.forename: Burkhard
authors.initials: B
authors.lastname: Jakob
authors.forename: Marco
authors.initials: M
authors.lastname: Durante
authors.forename: Gisela
authors.initials: G
authors.lastname: Taucher-Scholz
mesh_terms: D000818:Animals; D002843:Chromatin / Q000235:genetics*; D041321:Chromosomes, Human, X / Q000235:genetics* / Q000528:radiation effects; D004249:DNA Damage / Q000235:genetics* / Q000528:radiation effects; D004260:DNA Repair / Q000235:genetics*; D005260:Female; D005347:Fibroblasts / Q000378:metabolism / Q000473:pathology*; D005455:Fluorescent Antibody Technique; D006570:Heterochromatin / Q000235:genetics*; D006657:Histones / Q000235:genetics / Q000378:metabolism; D006801:Humans; D051379:Mice; D041681:NIH 3T3 Cells
chemical_list: D002843:Chromatin; C468783:H2AX protein, human; D006570:Heterochromatin; D006657:Histones
keywords: Chromocenter; DNA damage response; Heterochromatin; Inactive X chromosome; Particle irradiation