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| Heidelberg,
Thursday 24 November 2005 |
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| The earliest animals had human-like genes |
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![Detlev Arendt [left], Florian Raible and Peer Bork.](../../../../../images/press/press05/press24nov05spic.jpg) |
| Detlev Arendt [left], Florian Raible and Peer Bork. |
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Press
Release 24 November 2005 [PDF]
[Deutsch]
Species evolve at very different rates, and the
evolutionary line that produced humans seems to
be among the slowest. The result, according to a
new study by scientists at the European Molecular
Biology Laboratory [EMBL], is that our species has
retained characteristics of a very ancient ancestor
that have been lost in more quickly-evolving animals.
This overturns a commonly-held view of the nature
of genes in the first animals. The work appears
in the current issue of the journal Science.
Genes hold the recipes for proteins. The genes of
animals usually contain extra bits of DNA sequence,
called introns – information which has to
be removed as cells create new molecules. The number
of introns in genes, however, varies greatly among
animals. While humans have many introns in their
genes, common animal models such as flies have fewer.
From an evolutionary perspective, it was long assumed
that the simpler fly genes would be more ancient.
The current study reveals the opposite: early animals
already had a lot of introns, and quickly-evolving
species like insects have lost most of them.
To discover what early animals were like, scientists
usually compare their descendents. This is difficult
when comparing distantly-related animals such as
humans and flies. In these cases, it helps to look
at living organisms that have preserved many features
of their ancestors. Detlev Arendt's group is doing
this with a small marine worm called Platynereis
dumerlii. "Similar animals are already found
in the earliest fossils from the Cambrium, about
600 million years ago," Arendt explains, "arguing
that Platynereis could be something like
a 'living fossil'." This makes it an ideal model
for evolutionary comparisons to find out what the
common ancestors of humans, flies and worms were
like."
Until quite recently,
such comparisons could only be made by looking at
physical characteristics such as the structure of
bones, teeth, or tissues. But DNA sequencing now
permits scientists to make comparisons of the genetic
code and read evolutionary history from it. An international
consortium involving researchers from EMBL, the
UK, France and the United States has now sequenced
a part of the Platynereis genome. "The fraction
of Platynereis genes we have been able to look at
tells a very clear story," says researcher Florian
Raible, who performed most of the computer analyses.
"The wormÕs genes are very similar to human genes.
That's a much different picture than we've seen
from the quickly-evolving species that have been
studied so far."
Raible is member of both Arendt's
group and a second EMBL lab, that of Peer Bork,
whose specialty is analyzing genomes by computer.
"Human genes are typically more complex than those
of flies," explains Bork. "Classicallystudied species
like flies have far fewer introns, so many scientists
have believed that genes have become more complex
over the course of evolution. There have already
been speculations that this may not be true, but
proof was missing. Now we have direct evidence that
genes were already quite complex in the first animals,
and many invertebrates have reduced part of this
complexity."
Not only are the introns there – the team
also discovered that their positions within genes
have been preserved over the last half a billion
years." This gives us two independent measurements
that tell the same story," Raible explains. "Most
introns are very old, and they haven't changed very
much in slowly-evolving branches of life, such as
vertebrates or annelid worms. This makes vertebrates
into something like 'living fossils' in their own
right."
The discovery that Platynereis also represents
a slowlyevolving branch of animal life has important
implications for the study of humans. "We've already
learned an incredible amount about humans from studies
of the fly," Arendt says. "The marine worm might
well give us an even better look at important conserved
processes. Another thing that this has shown us
is that evolution is not always about gain; the
loss of complexity can equally be an important player
in evolution."
Source article
Vertebrate-type intron-rich genes in the marine annelid Platynereis dumerilii
F. Raible, K. Tessmar-Raible, K. Osoegawa, P. Wincker,
C. Jubin, G. Balavoine, D. Ferrier, V. Benes, P.
de Jong, J. Weissenbach, P. Bork and D. Arendt.
Science, 25 November 2005
Press contact
Sarah Sherwood
EMBL Information Officer, European Molecular Biology
Laboratory, Meyerhofstrasse 1, 69117 Heidelberg,
Germany
Tel: +49 [0] 6221 387-125
E-mail: sarah.sherwood@embl.de |
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