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extend life span in worms also lengthen
the animals’ fertile period. Those experiments found that certain mutations in
biological processes regulated by insulin prolong worms’ lives and give them
about three extra fertile days. Mutations in a different biological process,
controlled by a protein
called TGF-beta, extend fertility but not life span. But
the older TGF-beta mutant
mothers’ muscles get too
weak to lay eggs, and the
animals essentially die in
childbirth, Murphy said.
In the new study, the
researchers examined which
genes are turned on or off to
prolong life and fertility in the oocytes
and other body cells of the long-lived
worms.
“We were really surprised to find this
was a completely different mechanism”
controlling aging in eggs compared with
other body cells, Murphy said. “In fact,
there was almost no overlap between
the genes involved in the long life of
worms and those that extend fertility
in the oocytes.”
Body, or somatic, cells are known to
turn on stress-management genes to
protect proteins and change metabo-
lism as they age. But oocytes don’t
bother with guarding proteins, Murphy
and her colleagues found. Instead,
eggs ramp up production of factors
that protect them from or repair DNA
Because the entire job of
an egg is to provide genetic
information used to build a
new generation, it is perhaps
not so surprising that eggs
devote resources to making
sure the DNA stays healthy and chromo-
somes are allocated properly, said Craig
Blackstone, a physician and researcher
at the National Institute of Neurological
Disorders and Stroke in Bethesda, Md.
“It makes sense that this would happen,
but it hadn’t been shown before,” he said.
“It’s clever of her to study this.” s
“We were
really
surprised to
find this was
a completely
different
mechanism.”
COLEEN MURPHY
Eggs have own biological clock
By Tina Hesman Saey
Egg cells age differently than cells in the
rest of the body, a new study shows.
The finding, from experiments with
roundworms presented December 5,
might one day lead to ways to predict
how long women will stay fertile or even
to extend a woman’s fertile years.
Princeton University biologist Coleen
Murphy and her colleagues study aging
in the roundworm, Caenorhabditis
elegans. The worms typically live for
about 21 days, but their fertility drops
off sharply after the first week and the
worms can no longer reproduce after
they are about 9 days old. Even though
9-day-old worms still have plenty of eggs
left, the egg cells, or oocytes, are of such
poor quality they can’t produce embryos.
Women experience a similar sharp
decline in fertility starting in their late
30s. This drop-off in reproductive capability is one of the earliest signs of aging.
In earlier work, Murphy and her colleagues tested whether mutations that
Bacteria in bondage
Cells can trap some invading bacteria and slate them for
destruction, a new study shows. Serge Mostowy and Pascale
Cossart of the Pasteur Institute in Paris discovered that when
a type of diarrhea-causing bacteria called Shigella (blue) gets
inside cells, the cells fight back by encasing 10 to 30 percent
of the bacteria in cages made of proteins called septins (red).
the cells then digest the trapped bacteria in a cellular process
called autophagy, Cossart said December 4. the entrapment
strategy works only on bacteria that are actively grabbing
a cellular protein called actin and adding it to the cometlike
tails that the microbes use to propel themselves through the
cell. And the septins and autophagy proteins have to work
together: If either fails to latch on to a bacterium, the microbe
can escape. the findings could eventually help researchers
develop new therapies against Shigella and some other dis-ease-causing bacteria by boosting cage-building components.
— Tina Hesman Saey
S. MoStowy
www.sciencenews.org
