News: 'Junk' DNA proves functional

'Junk' DNA proves functional

In a paper published in Genome Research on Nov. 4, scientists at the Genome
Institute of Singapore (GIS) report that what was previously believed to be
"junk" DNA is one of the important ingredients distinguishing humans from
other species.

More than 50 percent of human DNA has been referred to as "junk" because it
consists of copies of nearly identical sequences. A major source of these
repeats is internal viruses that have inserted themselves throughout the
genome at various times during mammalian evolution.

Using the latest sequencing technologies, GIS researchers showed that many
transcription factors, the master proteins that control the expression of
other genes, bind specific repeat elements. The researchers showed that from
18 to 33% of the binding sites of five key transcription factors with
important roles in cancer and stem cell biology are embedded in distinctive
repeat families.

Over evolutionary time, these repeats were dispersed within different
species, creating new regulatory sites throughout these genomes. Thus, the
set of genes controlled by these transcription factors is likely to
significantly differ from species to species and may be a major driver for
evolution.

This research also shows that these repeats are anything but "junk DNA,"
since they provide a great source of evolutionary variability and might hold
the key to some of the important physical differences that distinguish
humans from all other species.

The GIS study also highlighted the functional importance of portions of the
genome that are rich in repetitive sequences.

"Because a lot of the biomedical research use model organisms such as mice
and primates, it is important to have a detailed understanding of the
differences between these model organisms and humans in order to explain our
findings," said Guillaume Bourque, Ph.D., GIS Senior Group Leader and lead
author of the Genome Research paper.

"Our research findings imply that these surveys must also include repeats,
as they are likely to be the source of important differences between model
organisms and humans," added Dr. Bourque. "The better our understanding of
the particularities of the human genome, the better our understanding will
be of diseases and their treatments."

"The findings by Dr. Bourque and his colleagues at the GIS are very exciting
and represent what may be one of the major discoveries in the biology of
evolution and gene regulation of the decade," said Raymond White, Ph.D.,
Rudi Schmid Distinguished Professor at the Department of Neurology at the
University of California, San Francisco, and chair of the GIS Scientific
Advisory Board.

"We have suspected for some time that one of the major ways species differ
from one another - for instance, why rats differ from monkeys - is in the
regulation of the expression of their genes: where are the genes expressed
in the body, when during development, and how much do they respond to
environmental stimuli," he added.

"What the researchers have demonstrated is that DNA segments carrying
binding sites for regulatory proteins can, at times, be explosively
distributed to new sites around the genome, possibly altering the activities
of genes near where they locate. The means of distribution seem to be a
class of genetic components called 'transposable elements' that are able to
jump from one site to another at certain times in the history of the
organism. The families of these transposable elements vary from species to
species, as do the distributed DNA segments which bind the regulatory
proteins."

Dr. White also added, "This hypothesis for formation of new species through
episodic distributions of families of gene regulatory DNA sequences is a
powerful one that will now guide a wealth of experiments to determine the
functional relationships of these regulatory DNA sequences to the genes that
are near their landing sites. I anticipate that as our knowledge of these
events grows, we will begin to understand much more how and why the rat
differs so dramatically from the monkey, even though they share essentially
the same complement of genes and proteins."

Source: Agency for Science, Technology and Research (A*STAR), Singapore
http://www.physorg.com/news145038245.html

Posted by
Robert Karl Stonjek


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