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| Heidelberg, 20 April 2007 |
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| The origin of the brain lies in a worm
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Researchers Detlev Arendt, Alexandru Denes and Gáspár Jékely |
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Researchers discover that the centralised nervous system of vertebrates is
much older than expected
Press
Release 20 April 2007 [PDF]
The rise of the central nervous system
[CNS] in animal evolution has puzzled scientists for centuries.
Vertebrates, insects and worms evolved from the same
ancestor, but their CNSs are different and were thought to have
evolved only after their lineages had split during evolution.
Researchers from the European Molecular Biology Laboratory
[EMBL] in Heidelberg now reveal that the vertebrate nervous system
is probably much older than expected. The study, which is
published in the current issue of Cell, suggests that the last common
ancestor of vertebrates, insects and worms already had a
centralised nervous system resembling that of vertebrates today.
Many animals have evolved complex nervous systems throughout
the course of evolution, but their architectures can differ substantially
between species. While vertebrates have a CNS in the shape
of a spinal cord running along their backs, insects and annelid
worms like the earthworm have a rope-ladder-like chain of nerve
cell clusters on their belly side. Other invertebrates on the other
hand have their nerve cells distributed diffusely over their body.
Yet, all these species descend from a common ancestor called
Urbilateria. If this ancestor already possessed a nervous system,
what it might have looked like and how it gave rise to the diversity
of nervous systems seen in animals today is what Detlev Arendt
and his group study at EMBL. To do so, they investigate the nervous
system of a marine annelid worm called Platynereis dumerilii.
"Platynereis can be considered a living fossil," says Arendt, "it still
lives in the same environment as the last common ancestors used
to and has preserved many ancestral features, including a prototype
invertebrate CNS."
Arendt and his group investigated how the developing CNS in
Platynereis embryos gets subdivided into the regions that later on
give rise to the different CNS structures. The regions are defined
by the unique combination of regulatory genes expressed, which
endow every type of neuron with a specific molecular fingerprint.
Comparing the molecular fingerpint of Platynereis nerve cells
with what is known about vertebrates revealed surprising similarities.
"Our findings were overwhelming," says Alexandru Denes, who
carried out the research in Arendt's lab. "The molecular anatomy
of the developing CNS turned out to be virtually the same in vertebrates
and Platynereis. Corresponding regions give rise to neuron
types with similar molecular fingerprints and these neurons
also go on to form the same neural structures in annelid worm
and vertebrate."
"Such a complex arrangement could not have been invented twice
throughout evolution, it must be the same system," adds Gáspár
Jékely, a researcher from Arendt's lab, who contributed essentially
to the study. "It looks like Platynereis and vertebrates have
inherited the organisation of their CNS from their remote common
ancestors."
The findings provide strong evidence for a theory that was first
put forward by zoologist Anton Dohrn in 1875. It states that vertebrate
and annelid CNS are of common descent and vertebrates
have turned themselves upside down throughout the course of
evolution.
"This explains perfectly why we find the same centralised CNS on
the backside of vertebrates and the bellyside of Platynereis,"
Arendt says. "How the inversion occurred and how other invertebrates
have modified the ancestral CNS throughout evolution
are the next exciting questions for evolutionary biologists."
Source Article
A.S. Denes, G. Jékely, D. Arendt et al., Conserved mediolateral molecular architecture of the annelid trunk neuroectoderm reveals
common ancestry of bilaterian nervous system centralisation, Cell, 20 April 2007
Press Contact
Anna-Lynn Wegener
Press Officer
EMBL Heidelberg
Tel: +49 6221 387-8452
Email: wegener@embl.de |
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