Pathways of DNA double-strand break repair during the mammalian cell cycle.
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It is shown here that NHEJ-defective hamster cells (CHO mutant V3 cells) have strongly reduced repair in all cell cycle phases after 1 Gy of irradiation, and HR is particularly important in late S/G2, where both pathways contribute to repair and radioresistance.Abstract:
Little is known about the quantitative contributions of nonhomologous end joining (NHEJ) and homologous recombination (HR) to DNA double-strand break (DSB) repair in different cell cycle phases after physiologically relevant doses of ionizing radiation. Using immunofluorescence detection of -H2AX nuclear foci as a novel approach for monitoring the repair of DSBs, we show here that NHEJ-defective hamster cells (CHO mutant V3 cells) have strongly reduced repair in all cell cycle phases after 1 Gy of irradiation. In contrast, HR-defective CHO irs1SF cells have a minor repair defect in G1, greater impairment in S, and a substantial defect in late S/G2. Furthermore, the radiosensitivity of irs1SF cells is slight in G1 but dramatically higher in late S/G2, while V3 cells show high sensitivity throughout the cell cycle. These findings show that NHEJ is important in all cell cycle phases, while HR is particularly important in late S/G2, where both pathways contribute to repair and radioresistance. In contrast to DSBs produced by ionizing radiation, DSBs produced by the replication inhibitor aphidicolin are repaired entirely by HR. irs1SF, but not V3, cells show hypersensitivity to aphidicolin treatment. These data provide the first evaluation of the cell cycle-specific contributions of NHEJ and HR to the repair of radiation-induced versus replication-associated DSBs.read more
Citations
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DNA repair in human pluripotent stem cells is distinct from that in non-pluripotent human cells.
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TL;DR: The results offer direct visual confirmation that γ-H2AX forms en masse at chromosomal sites of DNA double-strand breaks and suggest the possible existence of units of higher order chromatin structure involved in monitoring DNA integrity.
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Evidence for a lack of DNA double-strand break repair in human cells exposed to very low x-ray doses
Kai Rothkamm,Markus Löbrich +1 more
TL;DR: Evidence is presented that foci of γ-H2AX (a phosphorylated histone), detected by immunofluorescence, are quantitatively the same as DSBs and are capable of quantifying the repair of individual D SBs, allowing the investigation of DSB repair after radiation doses as low as 1 mGy, an improvement by several orders of magnitude over current methods.
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