Delayed Consequences of Changes in DNA Synthesis in Cells Exposed to Single Irradiation at the End of S Phase of the Mitotic Cycle

Kinetics of DNA synthesis throughout the mitotic cycle in mouse corneal epithelial cells after single γ-irradiation of cells (4 Gy) at the end of S phase was studied by the method of radioautography. It was found that single irradiation increased the duration of S phase due to reparation of damage in the cell at the expense of time that normally falls on g1 phase. During reparation, two parallel DNA synthesis processes occur in the damaged cells: de novo synthesis at the site of injury after excision of the damaged fragments (reparative synthesis) and supplementary synthesis during the repair period in the remaining undamaged genome competent for replication. During supplementary synthesis, repeats appear in DNA structure, which increases the amount of genetic material in the cell and affect S phase duration. All reparative processes take place in the cell population consisting of subpopulations of “differentiated”, “resting”, and “proliferating” cells. The changes in the proportions between the subpopulations under the influence of extreme factors can induce the appearance of metastatic cells in the population.