From: Alejandro Dubrovsky (s328940@student.uq.edu.au)
Date: Thu Jul 18 2002 - 13:56:35 MDT
(stolen from
http://news.yahoo.com/news?tmpl=story2&cid=570&ncid=753&e=3&u=/nm/20020718/sc_nm/science_brains_dc_1
)
Single Gene Makes Mice Big-Brained, Study Finds
Thu Jul 18, 2:05 PM ET
By Maggie Fox, Health and Science Correspondent
WASHINGTON (Reuters) - Adding an extra version of a single gene makes
mice grow big brains -- brains so large they have to fold up, much as
human brains do, to fit inside the skull, researchers said on Thursday.
It is not yet clear whether the mice are smarter -- they were all killed
soon after birth -- but the scientists said they were surprised that one
gene had such a strong effect and said they would do further
experiments.
"I know the most interesting question was whether they learned to play
Mozart but we don't know," Dr. Christopher Walsh of Brigham and Women's
Hospital and Harvard Medical School ( news - web sites) in Boston, who
led the study, said in a telephone interview.
"A bigger brain is not always good," he added, pointing out that a
condition called megacephaly, in which the cerebral cortex grows too
large, can cause mental retardation.
Walsh and colleague Anjen Chenn started with a protein called
beta-catenin, which helps control cell division.
"It is expressed in the brain in such a way that made us think it could
be a regulatory switch that makes cells stop dividing ... and become a
neuron," Walsh said. "Because neurons don't divide, that has to happen
for a cell to become a neuron."
Unlike cells in other tissues of the body, neurons stop dividing and
become fully formed before birth.
So Walsh and Chenn genetically engineered mice, adding extra
beta-catenin that would become overactive specifically in brain tissue.
To their surprise, they report in Friday's issue of the journal Science,
the mice developed large, folded brains that looked like human brains.
"We didn't expect to see the folds. We sort of expected the cerebral
cortex would be big. We didn't expect it to be so big," Walsh said.
Mouse brains normally have a smooth surface. Human brains are all
wrinkled and folded, because they are squashed into the skull.
Humans have disproportionately large brains for their size. Especially
large is the cerebral cortex, the surface layer made up of gray matter
-- the stuff involved in thought, as opposed to control of basic body
functions.
"The thinking power of the cerebral cortex is determined by surface
area. It is basically a sheet," said Walsh, a neurologist and
geneticist.
"If unfolded, it would be 10 times bigger than our head is. But the head
has to be small enough to come out of the mother's body at the right
time."
So in humans, it is stuffed in there, all folded up.
Walsh said one next step is to see if the beta-catenin gene is abnormal
in cases of mental retardation related to having a brain that is too big
or too small.
His team will also genetically engineer more mice and let them develop,
to see if they develop normally, and if they become more, or less,
intelligent than normal.
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