A review of dsb induction data for varying quality radiations

Abstract

Studies aimed at understanding the interactions of different types of radiation with cellular DNA have monitored the yields of DNA dsb versus radiation quality. Several techniques have been used to measure dsb yields in mammalian cells, and these include: neutral sedimentation gradients, filter elution and more recently pulsed field gel electrophoresis techniques (PFGE). Recent developments in PFGE have allowed the measurement of both the yields and the distribution of breaks within the genome, which go part of the way to explaining the RBE values close to 1.0 previously measured using other approaches with various radiation qualities. It is clear that future studies to determine the effectiveness of radiations of differing LET must use techniques that determine both yields and distributions of dsb, and assays need to be developed to allow these measurements at biologically relevant doses.

Different Roles for Nonhomologous End Joining and Homologous Recombination following Replication Arrest in Mammalian Cells

“…Thus, there was no relationship between induction of HR and the level of DSBs formed at stalled replication forks following treatment with equally toxic doses of thymidine. The level of fragmentation detected following a 3 mM hydroxyurea on May 10, 2018 by guest http://mcb.asm.org/ treatment corresponds to that found following a 50-Gy dose of ionizing radiation, which in turn corresponds to ϳ2,000 DSBs per cell (11,37). Given that the pulsed-field gel electrophoresis analysis used in this experiment can detect as few as 20 DSBs per cell (11), our results show that hydroxyurea produces at least 100-fold more DSBs than equally toxic doses of thymidine.…”

Extreme resistance of bdelloid rotifers to ionizing radiation

“…2 shows the gel electrophoretic distribution of DNA found after exposing A. vaga to doses in the range of 0 to 1,120 Gy. The average molecular sizes at 560, 840, and 1,120 Gy are 350, 250, and 190 kbp, respectively, with an average of 0.005 double-strand breaks (DSBs) Gy Ϫ1 ⅐Mbp Ϫ1 , a value within the range of 4 to 7 ϫ 10 Ϫ3 DSBs Gy Ϫ1 ⅐Mbp Ϫ1 measured by pulsedfield gel electrophoresis or sucrose sedimentation analysis for Escherichia coli, Saccharomyces cerevisiae, and diverse mammalian cell lines (9)(10)(11)(12). Some of the DSBs we observed may have arisen from non-DSB lesions as a result of high-temperature digestion, an effect estimated to cause about a 30% overestimate in ␥-irradiated mammalian cells (13).…”

Oxidative Stress Resistance inDeinococcus radiodurans

“…At 7 kGy, less than 3% of the DSBs are a result of double-event breaks (79). Radiation-resistant and radiation-sensitive species have remarkably similar numbers of DSBs per Gy per genome (0.002 to 0.006 DSBs/Gy/Mbp) (67,79,206,211,499,516,522) but differ in the amounts of oxidative DNA base damage (302). Furthermore, in D. radiodurans, aerobic conditions yield only 2.5-fold more DSBs/Gy than do anaerobic conditions (123).…”

“…Nonetheless, while efficiently protecting proteins against oxidative damage, neither manganese nor any other agent seems to protect DNA from doublestrand breakage during irradiation, as the numbers of DSBs per Gy per genome are similar for radiation-resistant and radiation-sensitive species (0.002 to 0.006 DSBs/Gy/Mbp) (67,79,206,211,499,516,522). DNA bases may still be protected against oxidation, as the amounts of oxidative DNA base damage per radiation dose per genome differ among organisms.…”