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Human Genome Yields Up More Secrets - washingtonpost.com
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Birney, who headed up the two-and-a-half year analysis of the ENCODE data, noted that just
1.5 percent of the "letters" in the genome actually make cellular proteins. So, his team
wondered, what was the other 98.5 percent doing?
"People rather dismissively called the rest of it 'junk DNA,' " he said. But the ENCODE data
suggest that this genetic material is, in fact, very active.
"One of the big surprises is that the regions between genes seem to be alive, not only with
regulatory regions -- which we suspected -- but also there's a lot of [gene] transcription," Birney
said. Transcription is the process whereby DNA transcribes its information into usable proteins.
The researchers also discovered another, less obvious purpose to a lot of genetic material.
They noticed that up to 70 percent of "functional regions" in the genomes of both humans and
other mammals were what Birney called "neutral." These neutral genetic blips popped up
frequently and didn't help or hinder the organism, in terms of activities needed to sustain life.
But Collins and other experts believe the neutral regions may, in fact, be key players in
evolution and disease, swinging into action occasionally and triggering either helpful or harmful
changes.
"It's like clutter in the attic," Collins said. "It's not the kind of clutter that you would get rid of
without consequences, however, because you might need it."
"Most of the time the human genome is operating on the 'first and second floor,' with maybe 5
percent of the genome doing whatever needs to be done in terms of daily activities," Collins
added. "But over evolutionary time, a much larger fraction of the genome -- this stuff up in the
attic -- becomes important. In fact, it's probably responsible for getting us where we are in
terms of [our] complexity. It's still there, waiting for natural selection to call upon it."
ENCODE is also revealing that epigenetics -- factors that modify the function of DNA but don't
change its sequence -- are a major player in disease.
For example, a team at the University of Virginia has found that the degree to which DNA is
bound within the chromosome's chromatin structure strongly influences whether that gene can
express, or produce, a protein.
While smaller studies have hinted at that before, "this genome-wide survey really shows that
these factors are beautifully coordinated," lead researcher Dr. Anindya Dutta, a professor of
molecular genetics at the university, toldHealthDay. "Portions of the chromosome that are
lightly packed are replicated early, and they also have the highest amount of gene expression."
That means that a too-loose or too-tight "packing" can cause changes in how a gene functions,
much like a mutation would. The ENCODE survey found that, "in cancer cells, this happens in
20 percent of our genes," Dutta noted.
Indeed, revelations from ENCODE should, in the long run, greatly enhance research into a
variety of diseases, the experts said. The findings come on the heels of a major study,
released last week inNature, in which British scientists substantially increased the number of
genes implicated in such common diseases as bipolar disorder, diabetes, heart disease and
rheumatoid arthritis.
http://www.washingtonpost.com/wp-dyn/content/article/2007/06/13/AR200706130...
6/13/2007