杏吧原创

GENES that help one creature live longer could hasten the death of another. A
new study shows that genetic variations that confer longevity in some fruit
flies often turn out to have adverse effects on flies of the opposite sex or
those in a different environment.

Researchers have found mutant forms of genes in flies and worms that lengthen
the animals鈥� lifespans, and hope to identify similar life-extending genes in
people. But whether certain genes can consistently lengthen lives is a matter of
debate. Studies in several organisms have shown that gender and environment
affect the behaviour of genes.

In an attempt to gauge the extent of these effects, Trudy Mackay at North
Carolina State University in Raleigh and her colleagues recorded the lifespans
of inbred male and female flies raised on different diets at different
temperatures. Using genetic mapping techniques, they then searched for genetic
variations that correlated with long lifespans.

Each of the 17 variations that Mackay鈥檚 team found increased longevity only
in certain environments, or in a sex-dependent manner, or both. Ten variations
that made flies live longer under some conditions made flies die sooner under
others. One variation, for example, made females live longer if they experienced
a hot spell early in life but die sooner if they lived at constant room
temperature, with no effect on males.

鈥淲hat鈥檚 really exciting about the study is its relevance to the evolution of
ageing,鈥� says John Tower, an expert on fruit fly ageing at the University of
Southern California. It highlights the fact that mutations that decrease
lifespan in some situations are nonetheless selected during evolution because
they prove beneficial under other circumstances.

James Curtsinger at the University of Minnesota in St Paul recently performed
similar studies, however, and found that environment or gender had virtually no
effect on longevity-associated genetic variations. Although he describes the
Mackay team as masters of fruit fly genome mapping, he believes their inbred
flies, derived from genetically unrelated stocks, might have genomes that are
unusually sensitive to the environment. 鈥淚 think there鈥檚 a serious limitation to
this study they do not fully appreciate,鈥� he says.

Mackay concedes that her lab-bred flies are genetically different to those
found in the wild, and that she needs to analyse other flies. But she points out
that studies of other animals, including humans, back the idea that environment
and gender alter the effects of genes. For example, geneticists at the
University of Calabria in Italy have discovered a genetic variation that seems
to make men, but not women, live longer.

If Mackay鈥檚 studies prove generally applicable, they might help explain other
contradictory genetic findings. 鈥淢any association studies have been done for
candidate genes affecting characters like alcoholism and Alzheimer鈥檚 disease,鈥�
says Mackay. 鈥淒ifferent researchers get different answers. One might wonder if
the environment accounts for some of these disparities.鈥�