Rad-2-dependent repair of radiation-induced chromosomal aberrations in Caenorhabditis elegans.

A method involving light microscopy was developed and utilized for the observation of gamma- or ultraviolet-induced aberrations of the chromosomes of Caenorhabditis elegans var. Bristol (N2). Gravid worms were irradiated and the chromosomes were examined in the early embryos derived from eggs fertilized after the irradiation. The frequency of gamma-induced aberrations in the early embryonic cells of C. elegans increased proportionally with the dosage of gamma-rays. It decreased greatly following incubation of the irradiated gravid worms for 2 days. This decrease was blocked by the rad-2 mutation but not by the rad-1 mutation of the same epistasis group. Both mutations make worms sensitive to radiation and chemicals. In addition, the hatchability of eggs laid by the rad-2 mutant after irradiation was restored very quickly as was that of the wild-type strain. Ultraviolet irradiation, on the other hand, induced few aberrations in both the wild-type and rad-1 strains, but it caused an elevated frequency of aberrations in the rad-2 strain. Ultraviolet irradiation strongly blocked the separation of chromosomes of the rad-2 strain. Furthermore, hatchability was very low in eggs laid by ultraviolet-irradiated rad-2 worms. These results suggest the existence of a rad-2-dependent mechanism for gonadal repair of chromosomal aberrations, including chromosomal non-separation, and indicate that gamma-induced chromosome aberrations are not fatal to the hatching of Caenorhabditis elegans which has holocentric chromosomes.