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| Titel |
The unique skeleton of siliceous sponges (Porifera; Hexactinellida and Demospongiae) that evolved first from the Urmetazoa during the Proterozoic: a review |
| VerfasserIn |
W. E. G. Müller, Jinhe Li, H. C. Schröder, Li Qiao, Xiaohong Wang |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 4, no. 2 ; Nr. 4, no. 2 (2007-05-03), S.219-232 |
| Datensatznummer |
250001621
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| Publikation (Nr.) |
 copernicus.org/bg-4-219-2007.pdf |
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| Zusammenfassung |
Sponges (phylum Porifera) had been considered as an enigmatic phylum, prior
to the analysis of their genetic repertoire/tool kit. Already with the
isolation of the first adhesion molecule, galectin, it became clear that the
sequences of sponge cell surface receptors and of molecules forming the
intracellular signal transduction pathways triggered by them, share high
similarity with those identified in other metazoan phyla. These studies
demonstrated that all metazoan phyla, including Porifera, originate from one
common ancestor, the Urmetazoa. The sponges evolved prior to the
Ediacaran-Cambrian boundary (542 million years ago [myr]) during two major
"snowball earth events", the Sturtian glaciation (710 to 680 myr) and the
Varanger-Marinoan ice ages (605 to 585 myr). During this period the ocean
was richer in silica due to the silicate weathering. The oldest sponge
fossils (Hexactinellida) have been described from Australia, China and
Mongolia and are thought to have existed coeval with the diverse Ediacara
fauna. Only little younger are the fossils discovered in the Sansha section
in Hunan (Early Cambrian; China). It has been proposed that only the sponges
possessed the genetic repertoire to cope with the adverse conditions, e.g.
temperature-protection molecules or proteins protecting them against
ultraviolet radiation.
The skeletal elements of the Hexactinellida (model organisms
Monorhaphis chuni and Monorhaphis intermedia or
Hyalonema sieboldi) and Demospongiae (models Suberites
domuncula and Geodia cydonium), the spicules, are formed
enzymatically by the anabolic enzyme silicatein and the catabolic enzyme
silicase. Both, the spicules of Hexactinellida and of Demospongiae, comprise
a central axial canal and an axial filament which harbors the silicatein.
After intracellular formation of the first lamella around the channel and
the subsequent extracellular apposition of further lamellae the spicules are
completed in a net formed of collagen fibers.
The data summarized here substantiate that with the finding of silicatein a
new aera in the field of bio/inorganic chemistry started. For the first time
strategies could be formulated and experimentally proven that allow the
formation/synthesis of inorganic structures by organic molecules. These
findings are not only of importance for the further understanding of basic
pathways in the body plan formation of sponges but also of eminent
importance for applied/commercial processes in a sustainable use of
biomolecules for novel bio/inorganic materials. |
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