A segmentação é o segredo por detrás da extraordinária diversificação dos animais

terça-feira, julho 27, 2010

Segmentation Is the Secret Behind the Extraordinary Diversification of Animals

ScienceDaily (July 27, 2010) — Segmentation, the repetition of identical anatomical units, seems to be the secret behind the diversity and longevity of the largest and most common animal groups on Earth. Researchers from CNRS and Université Paris Diderot have shown that this characteristic was inherited from a common segmented ancestor thought to have lived 600 million years ago and whose presence "changed the face of the world."

An example of animal with highly-visible repeated anatomical units: a Vietnamese cave centipede (Credit: Copyright CNRS Photothèque / DEHARVENG Louis)

This discovery is published inScience on 16 July 2010.
What do centipedes, earthworms and humans have in common? They all feature the repetition of anatomically identical units along the axis running from the front to the rear of their bodies. This characteristic, which researchers call segmentation, is shared by three large groups of animals. It may not be obvious at first glance though, as the repeated segments can be hidden by a shell or be partially fused. The segments are nevertheless present, laid out along the bilateral axis in the trunk, abdomen or thorax.
The first of these animal groups is the arthropods, which include centipedes but also insects, spiders, scorpions and crustaceans, representing by far the largest group of animals on the planet. With the highest number of species and individuals, it makes up nearly 40% of animal biomass. Apart from centipedes, whose segmentation is impossible to miss, arthropods also include grasshoppers, crickets and shrimps. Vertebrates, another highly diverse group, come next. They comprise most familiar animals, including humans, and they represent an evolutionary success. In this group, segmentation is found in the vertebrae of the backbone and, at a finer anatomical scale, in the muscles and nerves that spread from the spinal cord. The final group is the annelid worms, whose body is almost entirely formed of identical segments, such as sea and earthworms. They are also very numerous in terms of species, though much less conspicuous.
Read more here/Leia mais aqui: Science Daily
Science 16 July 2010:
Vol. 329. no. 5989, pp. 339 - 342
DOI: 10.1126/science.1188913

Hedgehog Signaling Regulates Segment Formation in the Annelid Platynereis

Nicolas Dray,1,*,{dagger} Kristin Tessmar-Raible,2,3,* Martine Le Gouar,1,* Laura Vibert,1 Foteini Christodoulou,3Katharina Schipany,2 Aurélien Guillou,4 Juliane Zantke,2 Heidi Snyman,3 Julien Béhague,1,4Michel Vervoort,1,4 Detlev Arendt,3 Guillaume Balavoine1,4,{ddagger}
Annelids and arthropods share a similar segmented organization of the body whose evolutionary origin remains unclear. The Hedgehog signaling pathway, prominent in arthropod embryonic segment patterning, has not been shown to have a similar function outside arthropods. We show that the ligand Hedgehog, the receptor Patched, and the transcription factor Gli are all expressed in striped patterns before the morphological appearance of segments in the annelid Platynereis dumerilii. Treatments with small molecules antagonistic to Hedgehog signaling disrupt segment formation. Platynereis Hedgehog is not necessary to establish early segment patterns but is required to maintain them. The molecular similarity of segment patterning functions of the Hedgehog pathway in an annelid and in arthropods supports a common origin of segmentation in protostomes.
1 Centre de Génétique Moléculaire du CNRS, FRE 3144, Avenue de la Terrasse, 91189 Gif-sur-Yvette, France.2 Max F. Perutz Laboratories, Universität Wien, Dr. Bohr-Gasse 9, 1030 Vienna, Austria.3 Developmental Biology Unit, European Molecular Biology Laboratory, Heidelberg 69117, Germany.4 Institut Jacques Monod, CNRS—Université Paris–Diderot, 15 rue Hélène Brion, 75205 Paris cedex 13, France.
* These authors contributed equally to this work.
{dagger} Present address: Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT 06520–8103, USA.
{ddagger} To whom correspondence should be addressed. E-mail: balavoine.guillaume@ijm.univ-paris-diderot.fr
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