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MBE Advance Access originally published online on March 10, 2009
Molecular Biology and Evolution 2009 26(6):1333-1340; doi:10.1093/molbev/msp042
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© The Author 2009. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

Research Articles

Multiple Dicer Genes in the Early-Diverging Metazoa

Danielle de Jong*, Michael Eitel*, Wolfgang Jakob*, Hans-Juergen Osigus*, Heike Hadrys*,{dagger}, Rob DeSalle{ddagger} and Bernd Schierwater*,{dagger},{ddagger}

* Tieraerztliche Hochschule, Division of Ecology and Evolution, Hannover, Germany
{dagger} Department of Ecology and Evolutionary Biology, Yale University, New Haven, CT
{ddagger} American Museum of Natural History, Central Park West, New York, NY

E-mail: bernd.schierwater{at}ecolevol.de.

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 pathway. Although the complement of Dicer proteins has been investigated in many "higher" metazoans, there has been no corresponding characterization 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 1 [H1] and 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, whereas 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

Claudia Kappen, Associate Editor


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