Abstract
Three radiation sensitive mutant strains of Medaka which showed significant increase of malformation by irradiation at organogenesis stage were established. We reported that one of these strains, RIC1, showed higher incidence of malformation and lower hatchability compared to the wild-type CAB strain after gamma-irradiation at the morula and pre-early gastrula stages and has a defect in the repair of DNA double-strand breaks (DSBs). We examined the responses of early embryonic cells in the other mutants, RIC2 and RIC3. Genetical complementation analyses demonstrated that these three strains have mutation at three different genetic loci. After irradiation with 1Gy at the morula stage, although no significant increase of hatchability was observed in CAB strain embryos, lower hatchabilities than those of non-irradiated were shown in RIC2 and RIC3. Moreover, RIC2 was more sensitive than RIC1. The TUNEL assay showed higher frequency of apoptosis in RIC2 and RIC3 embryos immediately after gamma-irradiation at the pre-early gastrula stage. These results suggest that RIC2 and RIC3 show high radiation sensitivity even at early embryonic stages. However, the comet neutral assay showed that almost of all DSBs induced were rejoined within 1h after irradiation at the pre-early gastrula stage like CAB. This result suggests that the products of ric2 and ric3 gene are associated with DNA surveillance mechanisms except for DNA DSBs repair mechanism in which ric1 gene participates at early developmental stages.
