Methylating the Mind
By Elizabeth Quill
ScienceNOW Daily News
7 December 2007

All brain cells are the same, genetically speaking. Yet somehow they
play vastly
different roles, some directing movement, others participating in
language or
thought. Now, a study finds that a chemical known to turn genes on and
off may
be partially responsible for this division of labor. The results,
researchers
suggest, could help scientists better understand psychiatric and
neurological
diseases.
It takes more than genes to make people who they are. Identical twins,
for
example, can look and act differently even though they share the same
DNA
(ScienceNOW, 5 July 2005). Environmental factors likely contribute to
this
variation, but it also seems to depend on so-called epigenetic
phenomena,
activity that regulates genes without changing the DNA code
(ScienceNOW, 12
April 2006). In the 1960s, researchers found that the addition of a
molecule
called a methyl group to cytosine, one of the four building blocks of
DNA, could
turn off genes. Since then, scientists have found that this process,
called
methylation, can also turn genes on and that it is linked to cancer
(ScienceNOW,
31 January 2000) and short-term memory formation (ScienceNOW, 14
March).

Because no studies have surveyed methylation's role in assigning
marching orders
to brain cells, geneticist Andrew Feinberg and psychiatric
neuroscientist James
Potash, both of Johns Hopkins University in Baltimore, Maryland,
decided to
investigate. Along with their colleagues, they compared possible
methylation
sites on 807 genes in 76 samples from human brains. Among the regions
studied
were the cerebellum, which controls movement, and the cerebral cortex,
which
controls language and memory. The team found that methylation patterns
differed
by brain region, indicating that epigenetics helps divide up the
brain's
functions. These patterns proved more robust than differences in
methylation
linked to race, age, or sex, the team reports in the December issue of
The
American Journal of Human Genetics.

The study makes clear, Feinberg says, that "working on the brain
without
thinking about epigenetics is like working with a blindfold on." By
understanding normal methylation, he adds, researchers can begin to
look at
methylation gone wrong, possibly in autism, depression, bipolar
disease, and
schizophrenia.

Given that epigenetics has been shown to modify gene expression in
other parts
of the body, the brain results are not surprising, says psychiatrist
Schahram
Akbarian of the University of Massachusetts Medical School in
Worcester. "One
could say neuroscience is catching up with the rest of the field."

Source: Science
http://sciencenow.sciencemag.org/cgi/content/full/2007/1207/3?etoc