Abstract
The RIC1 is radiation-sensitive medaka mutant (Oryzias latipes) and the ric1 mutant embryos have the defect in the repair of DNA double-strand breaks induced (Aizawa et al. 2004). In this study, we established cultured cell lines from RIC1 and wild type CAB embryos (5-8 days), and performed long period time-lapse observation (0-24hours) of morphological changes induced by irradiation with γ-ray (10 Gy) to investigate the process of apoptotic cell death. CAB cells became fragmented in cell death within 10 hours after γ-ray irradiation. In contrast, γ-ray irradiation did not induce such a apoptotic cell death in RIC1 cells. Immediately after γ-ray irradiation, cell arrest was observed in CAB and RIC1 cells. While CAB cells did not restart proliferation up to 24 hours after irradiation, RIC1 cells started to proliferation again 14-18 hours after γ-ray irradiation. To investigate cell cycle checkpoint in detail, we analyzed cell cycle with flow cytometry. The percentage of G2 phase CAB cells increased in 8 hours after γ-ray irradiation, indicating that γ-ray irradiation induced G2-M checkpoint in the CAB cells. In the RIC1 cells, though cell arrest was observed immediately after γ-ray irradiation, the percentages of G1 and G2 phase cells did not change in 24 hours after γ-ray irradiation. This result suggests that γ-ray irradiation induced G2-M and G1 checkpoint in the RIC1 cells. These results suggest the possibility that ric1 is the key gene relating DNA repair, cell cycle and cell death.
