SAGE Thoughts on Aging

The scientific method, and genetic analysis in particular, is based upon identifying variations between individuals of the same species. The study of Jones et al. in this issue reveals variation in transcript abundance between two developmental stages of the nematode Caenorhabditis elegans. In this case, the variation is not genetically specified but is induced by the environment as part of a shift to an alternate developmental form, the dauer larva. In this type of whole-genome analyses, it is assumed that such studies would reveal differences in transcript abundance that would be causally associated with distinct molecular and morphological transformations driving development. Much of this paper is conjecture about how the observed differences in transcript abundance specify observed differences in longevity (or, more precisely, in mortality rate).

C. elegans owes its existence as a species (a very successful, cosmopolitan species at that) to its ability to perform two critical tasks: finding new food resources and producing new progeny. In the wild, these events are temporally separated and involve continual transitions between the migratory food-seeking stage (the dauer) and the reproductive stage most commonly studied in the lab. The long-livedage-1mutant (see Braeckman et al. [2001] for the most recent comprehensive review on long-lived mutants), has a subtle change in its ability to transit between the dauer and the reproductive stages. This alteration does not affect its ability to grow when on plentiful food; however, under varying food conditions the age-1 mutation leads to a rapid loss of the mutant form in competition with wild type (Walker et al. 2000).

The dauer is not an immobile spore; it is highly migratory and this stage is almost certainly responsible for the cosmopolitan nature of this 1-mm invertebrate. Dauers survive for several months, showing negligible senescence (T.E. Johnson and P.M. Tedesco, …