Workshop on Pattern Formation and Functional Morphology, Tue, 08 Jan, 2008
Speaker: Thomas Holstein
Abstract
Cnidarians are the simplest metazoan animals with a nervous system and they are well known for their remarkable regeneration capacity. In the freshwater polyp hydra new polyps even regenerate from dissociated single cells by the process of de novo pattern formation. This process is based on the restoration of a signaling centre, i.e., an organizer. We are interested in the signaling cascades that constitute the regulatory network required for the robust patterning of this ancient signaling centre.
We identified wnt genes from the freshwater polyp hydra and the sea anemone Nematostella vectensis, a species representing the most basal group within the cnidarians. We found a so far unpredicted ancestral diversity within the Wnt family of cnidarians which have at twelve of the thirteen known wnt gene subfamilies in common; five subfamilies where lost in the protostome lineage. The expression patterns of wnt genes during N. vectensis embryogenesis show that these genes have distinct roles in gastrulation, resulting in serial and overlapping expression domains along the oral-aboral axis of the planula larva. Similar overlapping expression patterns of wnt genes in the freshwater polyp Hydra indicate that wnt genes have also distinct roles during the formation of the Hydra head organizer during regeneration. Furthermore, Dkk, a major antagonist of Wnt ligands previously known only from chordates exhibits a similar and conserved function in hydra. Furthermore, also the BMP/Chordin pathway is active in the regeneration process, indicating a permissive function of Chordin for organizer formation.
The unexpectedly high level of genetic complexity of signalling molecules evolved in early multi-cellular animals about 650 Myr ago and suggests a radical expansion of the genetic repertoire, concurrent with the evolution of multi-cellularity. Our data emphasize the crucial function of wnt/dkk and bmp/chordin signalling in an ancient metazoan signaling centre and in the diversification of eumetazoan body plans.
Funded by the German Science Foundation (DFG).
URL: www.ricam.oeaw.ac.at/specsem/ssqbm/participants/abstracts/index.php
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