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CHAMPAIGN -- The queen honey bee is
genetically identical to the workers in her hive, but she lives 10
times longer and -- unlike her sterile sisters -- remains
reproductively viable throughout life. A study from the University
of Illinois sheds new light on the molecular mechanisms that account
for this divergence. The study appears in the online edition of the
Proceedings of the National Academy of Sciences.
The research centers on the interplay
of three factors known to have a role in reproduction, growth and
longevity. The first, vitellogenin (Vg), is a yolk protein important
to reproduction but which also has been found to contribute to
longevity in worker bees. The second, juvenile hormone, contributes
to growth and maturation. The third, an insulin-IGF-1 signaling
pathway, regulates aging, fertility and other important biological
processes in invertebrates and vertebrates.
The study explores these factors in
queen honey bees. How, the researchers wanted to know, could the
queen achieve such a long life compared with her sisters while also
devoting so much energy to reproduction?
"Many times the way organisms achieve
longevity is via a tradeoff with reproduction," said
entomology
professor Gene Robinson, principal investigator on the study. "In
general, life forms that postpone reproduction until later in life
live longer. But the queen bee has her cake and eats it too. She's
an egg-laying machine. She lays 2,000 eggs a day and yet lives 10
times longer than individuals that stem from the same genome and yet
do not reproduce." The
researchers knew from studies of the fruit fly and nematode that the
insulin-signaling pathway had a role in longevity. Down-regulation
of insulin-IGF-1 signaling (IIS) in those species was associated
with increases in longevity -- but at the expense of fertility.
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 They also knew that manipulating
fat body cells in the head of the fruit fly influenced longevity.
Because Vg is synthesized in fat body cells in honey bees, the team
decided to look at Vg expression in the head and thorax as well as
the abdomen. This led to an
important discovery. Expression of Vg was high in the abdomen in the
young queen and declined over time but increased with age in the
head and thorax. Old queens showed much higher Vg expression than
young queens. Worker bees had
much lower levels of Vg expression than queens, and Vg in worker
heads was also low compared with queens. Previous studies in workers
had shown that Vg reduced oxidative stress in honey bees by
scavenging free radicals that can lead to aging or illness. Not
surprisingly, queens were more resistant to oxidative stress than
workers.
 Whether this is the
actual mechanism by which queens achieve both fertility and long
life remains to be seen, Robinson said. In any event, this study
suggests that vitellogenin plays a vital role in queen bee
longevity, he said, particularly since the honey bee lacks many
antioxidants commonly found in other species.
"There are implications here (for
other species) in the sense that here is an organism that is
reproductively active and long-lived," said Robinson, who is also
affiliated with the Institute for Genomic Biology. "And we see novel
and conserved factors that are part of a large regulatory network.
The queen has her cake and eats it too. And humans want to know how
that works."
[Text copied from
University
of Illinois news release]
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