DNA double-strand breaks measured in individual cells subjected to gel electrophoresis.
Microscopic examination of individual mammalian cells embedded in agarose, subjected to electrophoresis, and stained with a fluorescent DNA-binding dye provides a novel way of measuring DNA damage and more importantly, of assessing heterogeneity in DNA damage within a mixed population of cells. With this method, DNA double-strand breaks can be detected in populations of cells exposed to X-ray doses as low as 5 Gy. The radiation dose-response relationship for initial formation of double-strand breaks was identical for cell lines irradiated in G1, regardless of their sensitivity to killing by ionizing radiation. However, for cells irradiated in S phase, DNA migration was significantly reduced. For Chinese hamster V79 cells, Chinese hamster ovary cells, WiDr human colon carcinoma cells, and L5178Y-R mouse lymphoblastoid cells, S-phase DNA appeared to be about 3 times less sensitive to X-ray damage than DNA from other phases of the cell cycle. However, for the very radiosensitive L5178Y-S cells, the migration of replicating DNA was reduced only slightly. For Chinese hamster V79 and Chinese hamster ovary cells, damage was repaired at a similar rate in all cells of the population, and 85% of the breaks were rejoined within 2 h after irradiation. The radiosensitive L5178Y-S cells repaired damage more slowly than V79 or Chinese hamster ovary cells; 2 h after exposure to 50 Gy, approximately 50% of the damage was still present.
Olive
P L
PL
British Columbia Cancer Research Centre, Vancouver, Canada.
Wlodek
D
D
Banáth
J P
JP
D000818:Animals; D002478:Cells, Cultured; D004247:DNA / Q000737:chemistry / Q000187:drug effects / Q000528:radiation effects* / Q000648:ultrastructure; D004249:DNA Damage; D004260:DNA Repair; D004307:Dose-Response Relationship, Radiation; D004587:Electrophoresis, Agar Gel
D004247:DNA