by Ilan Gattegno, Israel Hayom Staff and Reuters
Israeli scientists discover cellular equivalent of "on/off" switches in DNA, explaining differences between modern humans and extinct Neanderthals • Paleoanthropologist Chris Stringer calls research "pioneering," and "a remarkable breakthrough."
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A
replica of a Neanderthall skull
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Photo credit: Reuters
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Breakthrough Israeli research published in the online
edition of the prestigious journal "Science" may explain what separates modern
man, or Homo sapiens, from Neanderthals.
How can creatures as different in body and mind as
present-day humans and their extinct Neanderthal cousins be 99.84 percent
identical genetically?
Four years after scientists discovered that the two
species' genomes differ by a fraction of a percent, geneticists said on Thursday
they have an explanation: the cellular equivalent of "on/off" switches that
determine whether DNA is activated or not.
The discovery also underlines the power of those on/off
patterns. Together, they add up to what is called the human epigenome, to
distinguish it from the human genome. The genome is the sequence of 3 billion
molecules that constitute all of a person's DNA while the epigenome is which
bits of DNA are turned on or off even as the molecular sequence remains
unchanged.
In the last few years, research on the epigenome has shed
light on how gene silencing leads to cancer, for instance, and how identical
twins with identical DNA sequences can be very different. The epigenome exerts
such powerful effects that it is often called the "second genetic code."
Now it has offered clues to what makes modern humans
distinct.
For the new study, geneticists led by Liram Carmel of the
Hebrew University of Jerusalem started with DNA from limb bones: those of a
living person, a Neanderthal and a Denisovan, an extinct human that lived in
Eurasia during the Stone Age and whose remains -- a pinkie bone and a tooth,
from a cave in Siberia -- were not discovered until 2010.
Geneticist David Gokhman and others on the Israeli team
then examined the DNA's on/off patterns, identifying about 2,200 regions that
were activated in today's humans, but silenced in either or both extinct
species, or vice versa. When a gene is silenced, it does not produce the trait
it otherwise would.
Chief among the epigenetic differences: a cluster of five
genes called HOXD, which influences the shape and size of limbs, including arms
and hands. It was largely silenced in both ancient species, the scientists
found.
That may explain anatomical differences between archaic
and present-day humans, including Neanderthals' shorter legs and arms,
bowleggedness, large hands and fingers, and curved arm bones.
Calling the work "pioneering," and "a remarkable
breakthrough," paleoanthropologist Chris Stringer of the Natural History Museum
in London said in an interview that the HOXD gene finding "may help to explain
how these ancient humans were able to build stronger bodies, better adapted to
the physical rigors of Stone Age life."
One caveat about the research is that one person's
epigenome can vary markedly from another's due to diet, environment and other
factors. It is therefore impossible to know whether the on/off patterns found in
Neanderthal genes are typical of the species overall or peculiar to the
individual studied.
Other DNA with big differences in on/off patterns between
the extinct and present-day humans is associated with neurological and
psychiatric disorders including autism, schizophrenia and Alzheimer's disease.
More of the Neanderthal versions were silenced.
In an interview, Carmel speculated that any given gene
might "do many things in the brain." When dozens of brain-related genes became
more active in today's humans, that somehow produces the harmful side effect of
neurological illness.
But the main effect might have been the astonishing leap in brain
development that most distinguishes modern Homo sapiens from our extinct
ancestors.
Ilan Gattegno, Israel Hayom Staff and Reuters
Source: http://www.israelhayom.com/site/newsletter_article.php?id=16953
Copyright - Original materials copyright (c) by the authors.
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