In preparing for a discussion of the stress resistance of age-1 mutants in C. elegans, Ayyadevera et al (2008) review the literature to answer this question.
The biggest changes in lifespan from a single gene mutation are in the range of 3-fold for C. elegans hermaphrodites, slightly less than 2-fold in Drospholia, and between 1.3-1.5 fold in mice. When you combine multiple genomic mutations with caloric restriction or germ-cell laser ablation, you can see increases in lifespan of up to 4-6 fold in C. elegans or 1.7 fold in mice. Some of these mutations also yield resistance to a number of stressors (such as thermotolerance), although some of them come with adverse side effects such as diminished fertility.
Ayyadevera’s team conducted an experiment to test the phenotype of age-1’s offspring, which were previously believed to have extremely diminished lifespans. They show that if they develop in low temperatures of 15-20 degrees C, they develop well and indeed have enhanced lifespans compared to wildtype nematodes. What does this reveal about the function of the age-1 gene? Further research will be necessary to bear out these results.
Ayyadavera S, Alla R, Thaden JJ, Shmookler Reis RJ. 2008 Remarkable longevity and stress resistance of nematode PI3K-null mutants. Aging Cell 7:13-22.