184 Age-related molecular variability in Caenorhabditis elegans, T. R. Golden et al. average genome copy number of 252 copies per worm at 4 days of age. Even when grown at the permissive temperature (Supplementary Fig. S4), the glp-4 mutant contained less than half as many genome copies as N2 at 5 days of age, as measured by qPCR. This leads us to hypothesize that the mutation in this strain, which has not been mapped, causes some type of DNA damage that interferes with the quantitative PCR. The biological significance of the DNA masses is unknown; these masses are so large that they might be expected to impact the health of the worm. Additionally, the synthesis of the DNA in the masses must represent a substantial allocation of resources. For these reasons, we suspect that the masses should be considered as an age-related pathology that might contribute to morbidity or even mortality of the worm. In this regard, it is interesting that the longer-lived daf-2 strains do not experience Fig. 5 Nuclear genome copy number in individual nematodes with age. Quantitative polymerase chain reaction (qPCR) was used to quantify the number of nuclear genomes in individual nematodes. (a) N2 hermaphrodites; (b) daf- 2(e1370) hermaphrodites, (c) N2 males, (d) N2 hermaphrodites raised on FUDR. Each symbol represents an individual nematode, 15 individuals per strain per age were assayed. The results shown are for chromosome II, but agree with results obtained for genes on chromosomes I and III (R2 = 0.96) for the same individuals. Fig. 6 Nuclear genome copy number in individual nematodes with age. Same data as shown in Fig. 5, with an expanded scale revealing the decline in nuclear genome copy number with age in daf- 2(e1370) hermaphrodites (b), N2 males (c) and N2 hermaphrodites raised on FUDR (d). the same proliferation of DNA. However, FUDR exposure, which prevents mass accumulation, does not extend lifespan in C. elegans (Gandhi et al., 1980). This may be analogous to the situation that would exist if cancer were removed from the human population, which has been argued would have only a minor impact on expected mean lifespan (Olshansky et al., 1990). Removal of one cause of death from a population does not necessarily change the rate of aging (i.e., the increase in the probability of death with time); death, per se, is perhaps not the best metric for the study of aging. As they age, both wild-type and long-lived strains of C. elegans appear to lose the tight regulation held over nuclear DNA copy number apparent in young adults (Fig. 5a,b). In N2, the variance in genome content reaches a maximum as the mortality rate of a population begins to increase, and correlates with the © Blackwell Publishing Ltd/Anatomical Society of Great Britain and Ireland 2007 No claim to original US government works