New research on the Drosophila melanogaster fruit fly species yields results that support the mutation accumulation (MA) theory of ageing:
The other, more widely accepted theory of antagonistic pleiotrophy (AP) says that aging occurs when genes that offer help during the reproductive years -- those that produce estrogen, for example -- take on harmful roles later in life. Selection under AP theory favors the early life effects because these lead to the production of offspring but does not oppose the deleterious effects in late life, Hughes said. Building on her theoretical study of age-related inbreeding depression and genetic variability (PNAS, June 1996) while a doctoral student at the University of Chicago, Hughes and colleagues raised fruit flies to test the effect of delayed mutations.
The new study found that the deleterious effects of mutations on reproduction rose dramatically with age during the reproductive years in both genotypes -- homozygous (those with many identical genes, or inbreeding) and heterozygous (those having a variety of genes present). Reproductive success declined more rapidly, however, in the homozygous lines, as predicted by the MA theory.
"This study allowed us to detect certain kinds of genetic effects called dominance variance that are predicted to increase with age only under the MA theory," Hughes said. "The power to detect these effects is critical to tests of evolutionary aging theories, because an age-related increase appears to be a unique prediction of the MA theory, while other kinds of genetic effects can increase under either model."
There are other explanations for aging aside from the mutation accumulation (MA) theory. It is likely that aging is caused by an assortment of changes. For instance, cells accumulate trash molecules (eg lipofuscin) that the cells are unable to break down or expel. One way to solve assorted aging problems for cells that can be replaced is to replace them with younger cells. If an organ or reservoir of cells is replaced then all the aging effects for that group of cells are eliminated until the damage accumulates again. However, there are cell types for which it is far more preferable to repair than to replace (eg brain cells). So treatments utilizing both approaches will be developed.
|Share |||Randall Parker, 2002 November 06 05:34 PM Aging Reversal|