Contribution of sponge genes to unravel the genome of the hypothetical ancestor of Metazoa (Urmetazoa)

Recently the term Urmetazoa, as the hypothetical metazoan ancestor, was int roduced to highlight the finding that: all metazoan phyla including the Por ifera (sponges) are derived from one common ancestor. Sponges as the evolut ionarily oldest, still extant phylum, are provided with a complex network o f structural and functional molecules. Analyses of sponge genomes from Demo spongiae (Suberites domuncula and Geodia cydonium), Calcarea (Sycon raphanu s) and Hexactinellida (Aphrocallistes vastus) have contributed also to the reconstruction of the evolutionary position of Metazoa with respect to Fung i. Furthermore, these analyses have provided evidence that the characterist ic evolutionary novelties of Metazoa, such as the extracellular matrix mole cules, the cell surface receptors, the nervous signal transduction molecule s as well as the immune molecule existing in Porifera, share high sequence and in some aspects also functional similarities to related polypeptides fo und in other metazoan phyla. During the transition to Metazoa new domains o ccurred; as one example, the formation of the death domain from the ankyrin is outlined. In parallel, domanial proteins have been formed, such as the receptor tyrosine kinases. The metazoan essentials have been defined by ana lyzing and comparing the sponge sequences with the related sequences from t he metazoans Homo sapiens, Caenorhabditis elegans and Drosophila melanogast er, the fungus Saccharomyces cerevisiae and the plant Arabidopsis thaliana. The data revealed that those sponge molecules grouped to cell adhesion cel l recognition proteins are predominantly found in Protostomia and Deuterost omia while they are missing in Fungi and Viridiplantae. Moreover, evidence is presented allowing the conclusion that the sponge molecules are more clo sely related to the corresponding molecules from H. sapiens than to those o f C elegans or D. melanogaster. Especially surprising was the finding that the Demospongiae are provided with elements of adaptive immunity. (C) 2001 Elsevier Science B.V. All rights reserved.