title: Identification of radiation-sensitive mutants in the Medaka, Oryzias latipes.
abstract: We screened populations of N-ethyl-N-nitrosourea (ENU)-mutagenized Medaka, (Oryzias latipes) for radiation-sensitive mutants to investigate the mechanism of genome stability induced by ionizing radiation in developing embryos. F3 embryos derived from male founders that were homozygous for induced the mutations were irradiated with gamma-rays at the organogenesis stage (48hpf) at a dose that did not cause malformation in wild-type embryos. We screened 2130 F2 pairs and identified three types of mutants with high incidence of radiation-induced curly tailed (ric) malformations using a low dose of irradiation. The homozygous strain from one of these mutants, ric1, which is highly fertile and easy to breed, was established and characterized related to gamma-irradiation response. The ric1 strain also 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. We found that the decrease in hatching success after gamma-irradiation, depends on the maternal genotype at the ric1 locus. Terminal deoxynucleotidyl transferase-mediated deoxy-UTP nick end-labeling assays showed a high frequency of apoptosis in the ric1 embryos immediately after gamma-irradiation at the pre-early gastrula stage but apoptotic cells were not observed before midblastula transition (MBT). The neutral comet assay revealed that the ric1 mutant has a defect in the rapid repair of DNA double-strand breaks induced by gamma-rays. These results suggest that RIC1 is involved in the DNA double strand break repair in embryos from morula to organogenesis stages, and unrepaired DNA double strand breaks in ric1 trigger apoptosis after MBT. These results support the use of the ric1 strain for investigating various biological consequences of DNA double strand breaks in vivo and for sensitive monitoring of genotoxicity related to low dose radiation.
authors.affiliation: Department of Integrated Biosciences, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa-no-ha 5-1-5, Kashiwa, Chiba 277-8572, Japan.
authors.forename: Kouichi
authors.initials: K
authors.lastname: Aizawa
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Mitani
authors.forename: Nozomi
authors.initials: N
authors.lastname: Kogure
authors.forename: Atsuko
authors.initials: A
authors.lastname: Shimada
authors.forename: Yukihiro
authors.initials: Y
authors.lastname: Hirose
authors.forename: Takao
authors.initials: T
authors.lastname: Sasado
authors.forename: Chikako
authors.initials: C
authors.lastname: Morinaga
authors.forename: Akihito
authors.initials: A
authors.lastname: Yasuoka
authors.forename: Hiroki
authors.initials: H
authors.lastname: Yoda
authors.forename: Tomomi
authors.initials: T
authors.lastname: Watanabe
authors.forename: Norimasa
authors.initials: N
authors.lastname: Iwanami
authors.forename: Sanae
authors.initials: S
authors.lastname: Kunimatsu
authors.forename: Masakazu
authors.initials: M
authors.lastname: Osakada
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Suwa
authors.forename: Katsutoshi
authors.initials: K
authors.lastname: Niwa
authors.forename: Tomonori
authors.initials: T
authors.lastname: Deguchi
authors.forename: Thorsten
authors.initials: T
authors.lastname: Hennrich
authors.forename: Takeshi
authors.initials: T
authors.lastname: Todo
authors.forename: Akihiro
authors.initials: A
authors.lastname: Shima
authors.forename: Hisato
authors.initials: H
authors.lastname: Kondoh
authors.forename: Makoto
authors.initials: M
authors.lastname: Furutani-Seiki
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000528:radiation effects; D020552:Comet Assay; D004260:DNA Repair / Q000502:physiology; D005720:Gamma Rays; D005775:Gastrula / Q000502:physiology; D042822:Genomic Instability; D009154:Mutation; D009990:Oryzias / Q000196:embryology / Q000235:genetics*; D011836:Radiation Tolerance / Q000235:genetics*; D013623:Tail / Q000002:abnormalities / Q000196:embryology / Q000528:radiation effects; D013997:Time Factors