Life-Span Extension

Scientists use life extension as a way to find genes that affect aging. Johnson and Wood proposed in 1982 that genetic variants that lengthen life could be found. Most genetic alterations shorten life, because these mutants reduce overall health and fitness. Indeed, it is counterintuitive that a genetic mutant could actually lead to longer than normal life, because mutations are generally thought of as bad. However, to the species, the length of an individual life does not matter at all. Scientists have used this strategy very effectively and have discovered numerous genes that lengthen life span.

Aside from caloric restriction, genetic manipulation is the only intervention that has been widely shown to actually extend longevity. Initial studies used naturally occurring genetic variants of longevity genes and combined them to yield longer-lived populations. Later, mutations in individual genes were shown to generate even longer life spans than possible in strains developed using this polygenic approach. In invertebrates, and especially in the small nematode worm called Caenorhabditis elegans, genetic variants leading to prolonged life have been produced for almost two decades. Other model organisms, in addition to the nematode, that are used to study genetic interventions include yeast and the fruit fly. These studies are yielding dozens of genes that affect longevity and slow down the rate of aging.

Several steps must be taken to characterize a longevity mutant. First, it must be verified that the longevity change is real and is passed on to the offspring. If it is, and if the mutation can be assigned a position in the chromosomes of the animal, then a mutational event has likely been found. Then the scientist would want to fish out the larger piece of DNA that carries the genetic mutants and figure out what this larger piece of DNA (the gene) does. Since almost all genes code for protein, this means finding out what the protein does, using both biochemical and genetic tricks.