Heterochromatinization associated with cell differentiation as a model to study DNA double strand break induction and repair in the context of higher-order chromatin structure

Inhibition of H3K4me2 Demethylation Protects Auditory Hair Cells from Neomycin-Induced Apoptosis

“…Cross talk between posttranslational modifications has been proposed to create an epigenetic code that affects chromatin structure and other genome functions, such as DNA repair and replication [27][28][29]. This interaction, especially the importance of histone methylation, has been highlighted in the transcription regulation and epigenetic inheritance [30].…”

Chromatin differentiation of white blood cells decreases DSB damage induction, prevents functional assembly of repair foci, but has no influence on protrusion of heterochromatic DSBs into the low-dense chromatin

“…Despite this fact, γH2AX foci protrude from Hc into nuclear subcompartments with low chromatin density. Our living cell observations suggest that 53BP1 can penetrate into the interior of dense Hc domains only after their decondensation [2]. Conclusions: We show that Hc is less sensitive to DSB induction by gamma rays but not heavy ions; lower Hc hydratation and higher protein density (when compared with euchromatin) probably reduce formation of free radicals and increase their sequestration, respectively.…”

“…At least some DSB repair proteins (e.g. 53BP1) are expressed and γH2AX foci still occur in immature granulocytes and monocytes [2,5]; however, the colocalization of γH2AX with 53BP1 is low and the majority of DSBs are not repaired. Despite this fact, γH2AX foci protrude from Hc into nuclear subcompartments with low chromatin density.…”

“…We also studied, how is the sensitivity to DSB induction, assembly of repair foci and processing of DSBs influenced by the differentiation-induced changes in chromatin structure and composition. Materials and methods: Formation, localization (relative to higher-order chromatin domains) and mutual colocalization of γH2AX and p53BP1 repair foci have been studied together with DSB repair kinetics in spatially fixed human skin fibroblast and differently differentiated white blood cells (WBC) irradiated with gamma rays, protons of different energies [2,3], and 20 Ne ions (submitted). Immunostaining and ImmunoFISH were used in combination with high-resolution confocal microscopy [2,3] and living cell imaging [4].…”

Primary and secondary clustering of DSB repair foci and repair kinetics compared for -rays, protons of different energies and high-LET 20Ne ions

“…Though γH2AX/p53BP1 foci were positionally quite stable [ 2], ‘secondary clusters’ occasionally appeared after all kinds of irradiation during about 30 min PI. The formation of secondary clusters usually appeared due to the heterochromatin decondensation at the sites of heterochromatic DNA double-strand breaks (hcDSBs), followed by their protrusion into a limited space of nuclear subdomains of low density-chromatin (discussed in [ 1, 2, 5]). Conclusions: Primary clusters appear in cell nuclei immediately PI as the consequence of highly localized energy deposition, while secondary clusters develop during (and because of) DSB repair. Primary DSB clusters probably represent the main cause of chromosomal translocations induced with high-LET radiations while secondary clusters seem to be more important for low-LET γ-rays and protons.…”