Sister Chromatid Exchanges in Human Lymphocytes Exposed to Ionizing Radiation during G 0

Sister chromatid exchanges occur in G2-irradiated cells

“…Systematic investigations revealed that S-phase-dependent agents are generally strong inducers of SCEs, whereas ionizing radiation (IR), radiomimetic drugs or restriction enzymes are weak inducers. [6][7][8][9][10][11] Therefore, it became a common belief in the scientific community that cells have to pass through S phase to manifest SCEs after damage induction. [12][13][14] Although some investigators suggested models that involve non-homologous end-joining (NHEJ) in the generation of SCEs, the prevailing evidence suggests that homologous recombination (HR) is the underlying mechanism for SCE formation.…”

“…[15][16][17][18][19] As a result of the extensive research, the mechanism of formation of SCEs arising in cells after treatment with S-phase-independent clastogens such as IR was critically discussed. 8,9,14,16 For example, Mühlmann-Diaz and Bedford suggested that SCEs induced after γ-or X-irradiation might represent "false" SCEs that arise from chromosomal aberrations, in particular paracentric inversions, produced in G 0 /G 1 . 20 Color-jumps on chromatids were also observed in cells that were treated with DSB-inducing agents in G 2 , but these jumps were attributed to a two-lesion exchange process.…”

Effects of radiotherapy and chemotherapy on sister chromatid exchanges in peripheral lymphocytes of the patients with gynecologic cancer.

“…On the other hand, Galloway (1977) reported that, by X-ray irradiation (200 R) on human lymphocytes in the G0 and S phases, the SCE frequency of the GO phase cells decreased slightly than that of the control group. Littlefield et al (1979) irradiated 60Co on human TABLE 5. SCE frequency in cases undergoing chemotherapy lymphocytes in Go phase and found that changes in the SCE frequency were insignificant.…”

“…The increase of SCE frequency found by Perry and Evans (1975) following irradiation was due not only to the influence of BrdU in the culture fluid, but also due to the influence of the BrdU-absorbed DNA's reaction. We have used irradiation in vivo similar to that used by Littlefield et al (1979) in vitro, after which we sampled lymphocytes, cultured them in a medium containing PIIA and then added BrdU to it. Only by means of such a method, can the influences of radioactivity on natural DNA be accurately determined.…”

Insights into the mechanisms of sister chromatid exchange formation

“…Ionizing radiation is a poor inducer of SCEs and it is only effective when applied to cells in G 1 with chromosomes unifilarily substituted with BrdU (Littlefield et al, 1979;Renault et al, 1982). This fact gave rise to many debates about the nature of radiationinduced lesions responsible for SCEs, because ionizing radiation induces mainly single and double strand breaks which, when induced in G 1 , are expected to be repaired before the cell enters S-phase (Szumiel, 1998).…”