MBE Advance Access published online on March 10, 2009
Molecular Biology and Evolution, doi:10.1093/molbev/msp042
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Research Article |
Multiple Dicer genes in the early diverging Metazoa
1 Tieraerztliche Hochschule, Division of Ecology and Evolution, Buenteweg 17d, 30559, Hannover, Germany
2 American Museum of Natural History, 79th Street at Central Park West, New York, NY 10024
3 Department of Ecology and Evolutionary Biology, Yale University, New Haven, CT 06520-8104, USA
* Correspondence to: Prof. Dr. Bernd Schierwater, Tieraerztliche Hochschule, Division of Ecology and Evolution, Buenteweg 17d 30559, Hannover, Germany, Phone : (+49)-511-953-8880 Fax: (+49)-511-953-8584, email : bernd.schierwater{at}ecolevol.de
Received for publication October 31, 2008. Revision received February 10, 2009. Accepted for publication March 4, 2009.
Dicer proteins are highly conserved, are present in organisms ranging from plants to metazoans and are essential components of the RNA interference (RNAi) pathway. While the complement of Dicer proteins has been investigated in many ‘higher’ metazoans, there has been no corresponding characterisation of Dicer proteins in any early branching metazoan. We cloned partial cDNAs of genes belonging to the Dicer family from the anthozoan cnidarian Nematostella vectensis and two distantly related haplotypes ("species lineages") of the Placozoa (Trichoplax adhaerens 16S haplotype H1; Placozoa sp. H2). We also identified Dicer genes in the hydrozoan Hydra magnipapillata and the demosponge Amphimedon queenslandica with the use of publicly available sequence databases. Two Dicer genes are present in each cnidarian species, while five Dicer genes each are found in the Porifera and Placozoa. Phylogenetic analyses comparing these and other metazoan Dicers suggest an ancient duplication event of a ‘Proto-Dicer’ gene. We show that the Placozoa is the only known metazoan phylum which contains both representatives of this duplication event, and that the multiple Dicer genes of the basal metazoan phyla represent lineage specific duplications. There is a striking diversity of Dicer genes in ‘basal’ metazoans, in stark contrast to the single Dicer gene found in most ‘higher’ metazoans. This new data has allowed us to formulate new hypotheses regarding the evolution of metazoan Dicer proteins and their possible functions in the early diverging metazoan phyla. We theorize that the multiple placozoan Dicer genes fulfill a specific biological requirement, such as an immune defense strategy against viruses.
Key Words: Dicer • RNAi • Evolution • Placozoa • Cnidaria • Porifera