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Buns
of Steel
Excerpt
By Serena Gordon, HealthScoutNews
(HealthScoutNews) -- How would
you like to eat whatever you want, and have your body convert
almost all of it directly to muscle?
No problem -- as long as
you're a callipyge (cal-ah-PEEJ) sheep. Humans, sadly, will have
to wait awhile.
After more than 10 years
of searching, scientists have discovered the mutated gene that
causes callipyge (which means beautiful buttocks) sheep to have
large, muscular rear ends.
This discovery has scientists
excited for several reasons. First, they hope that by studying
the mutation, they can learn more about how muscle and fat are
deposited in the sheep, which might provide clues to how fat and
muscle are metabolized in humans. They're also excited because
it's given them a whole new way to search for elusive gene defects.
Their findings appear in the October issue of Genome Research.
It all started 20 years
ago when a Nebraska farmer noticed one of his sheep had a very
muscular bottom. "Callipyge sheep are like Arnold Schwarzenegger.
They have huge muscles with virtually no fat," says one of
the researchers, Randy Jirtle, a professor of radiation oncology
at Duke University Medical Center. The animals convert food into
muscle 30 percent more efficiently than normal sheep do, he says.
Once the farmer started
breeding the sheep, he noticed that only those born to large-bottomed
males carried the unusual trait. Because of this, scientists knew
they were searching for an imprinted gene -- rare genes that are
literally stamped with markings that turn off one parent's gene.
Normally, two copies of each gene are inherited -- one from the
mother and one from the father. One copy will be dominant and
the other recessive, but both will be present. This isn't so with
imprinted genes.
Jirtle, along with Brad
Freking, a geneticist with the U.S. Department of Agriculture,
and their colleagues searched through all of the known genes and
turned up nothing that could be responsible for the muscular mutation.
Then Freking and his team compared DNA from normal sheep to DNA
from the large-bottomed callipyge.
They found 600 distinct
markers, which are minute variations, in the gene sequence they
examined. Only one, however, was unique to callipyge sheep. What
was truly unusual, says Jirtle, is that they found this marker
in an area scientists had thought contained no genes, and that
such a minor mutation could have such a dramatic effect.
Jirtle says this is the
first time scientists have identified a gene through its mutation.
Usually, scientists look for genes, and only after a gene is identified
do they start searching for its mutations.
This new method of searching
for genetic mutations may help scientists solve the mystery of
certain disorders, such as autism or bipolar disorder, Jirtle
says. By comparing gene sequences in people who have the disorder
to people who don't, researchers may be able to zero in on where
the mutation is occurring.
"So, we're at the
end of the beginning," explains Jirtle, who says the researchers
now hope to figure out how this gene causes the change in metabolism,
which could ultimately be important in treating obesity.
"[This study] is
intriguing from several points of view," says Dr. Richard
Re, director of research for the Ochsner Clinic Foundation in
New Orleans. "The methodology appears to be atypical, and
the sheep have a very interesting system for fat-muscle balance."
However, he says it's too soon to know what impact this discovery
might have on obesity research in the future.
What To Do
This article from the
Harvard University Gazette and this one from the
Medical College of Wisconsin look at ways genes may affect
human obesity.
Reference
Source 101
For more information on how to prevent other diseases, use
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