To analyze the relationship between resistance to oxidative stress and longevity, we isolated three novel paraquat-resistant mutants, mev-5, mev-6, and mev-7, from the nematode Caenorhabditis elegans. They all showed the Dyf (defective in dye filling) phenotype, but not always resistance to heat or UV. Life-span extension was observed only in the mev-5 mutant at 26 C. These results indicate that longevity is uncoupled with the phenotype of paraquat resistance.Key words: Caenorhabditis elegans; oxidative stress; paraquat; aging; Dyf A number of hypotheses have been presented to account for the mechanism of aging. The free radical hypothesis of aging was first mentioned by Harman in the mid-1950s, 1) and since then has drawn much attention. Among the free radicals, reactive oxygen species (ROS) are most notable because they are generated in normal metabolic processes and damage cellular components such as proteins, DNA, and lipids. The resulting damage is thought to cause cellular dysfunction and eventually to lead to senescence. Animals have evolved various defense mechanisms against ROS, 2) but they appear to be far from perfect. Accumulating genetic evidence from model organisms such as the nematode, fruit fly, and mouse indicates a positive relationship between the longevity of mutant individuals and their capacity to resist oxidative stress.
3)But, much remains to be elucidated as regards defense mechanisms against ROS even in model organisms.To assess the above relationship, we employed genetic analysis using the nematode C. elegans as a model system, because it has been proved to be extremely useful for identifying responsible genes in mutants. We used paraquat (methyl viologen), which generates superoxide anions in cells, as an agent to isolate mutants with resistance to oxidative stress. 4) We mutagenized wild-type N2 worms with ethyl-methansulfonate and screened them by resistance to paraquat.We isolated three novel mutants, designated mev-5 (qa5005), mev-6 (qa5006), and mev-7 (qa5007). Their paraquat-resistant traits were all recessive and inherited by progeny in a Mendelian fashion. Their mutations were cleaned by back-crossing to N2 worms five times for subsequent analysis. Genetic analysis revealed that mev-5, mev-6, and mev-7 were concordant with the genetic markers dpy-11, dpy-1, and dpy-5 located on LG V, III, and I respectively. To map the genes regionally, three-factor-cross experiments were carried out, and the following results were obtained: mev-5 (4/4) (rol-4 unc-76), unc-42 (3/6) mev-5 (3/6) lon-3, (unc-45 dpy-1) (9/ 9) mev-6, dpy-1 (3/9) mev-6 (6/9) unc-32, dpy-1 (3/14) mev-6 (11/14) unc-93, (dpy-5 unc-37) (5/5) mev-7, dpy-14 (8/12) mev-7 (4/12) unc-29, mev-7 (7/7) (unc-29 dpy-24), (unc-40 bli-4) (2/2) mev-7 (Fig. 1A).Sensitivity to paraquat in the mev-mutants was determined as described previously.5) In brief, eggs were placed and incubated on plates containing various concentration of paraquat for 5 d, and the percentage of worms that reached adulthood was determined. Wildtype N2 worms h...