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MBE Advance Access originally published online on January 24, 2008
Molecular Biology and Evolution 2008 25(4):737-747; doi:10.1093/molbev/msn021
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© The Author 2008. 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

Concerted Evolution of Sea Anemone Neurotoxin Genes Is Revealed through Analysis of the Nematostella vectensis Genome

Yehu Moran*, Hagar Weinberger*, James C. Sullivan{dagger}, Adam M. Reitzel{dagger},1, John R. Finnerty{dagger} and Michael Gurevitz*

* Department of Plant Sciences, George S. Wise Faculty of Life Sciences, Tel-Aviv University, Tel-Aviv, Israel
{dagger} Department of Biology, Boston University

E-mail: mamgur{at}post.tau.ac.il.

Accepted for publication January 20, 2008.

Gene families, which encode toxins, are found in many poisonous animals, yet there is limited understanding of their evolution at the nucleotide level. The release of the genome draft sequence for the sea anemone Nematostella vectensis enabled a comprehensive study of a gene family whose neurotoxin products affect voltage-gated sodium channels. All gene family members are clustered in a highly repetitive ~30-kb genomic region and encode a single toxin, Nv1. These genes exhibit extreme conservation at the nucleotide level which cannot be explained by purifying selection. This conservation greatly differs from the toxin gene families of other animals (e.g., snakes, scorpions, and cone snails), whose evolution was driven by diversifying selection, thereby generating a high degree of genetic diversity. The low nucleotide diversity at the Nv1 genes is reminiscent of that reported for DNA encoding ribosomal RNA (rDNA) and 2 hsp70 genes from Drosophila, which have evolved via concerted evolution. This evolutionary pattern was experimentally demonstrated in yeast rDNA and was shown to involve unequal crossing-over. Through sequence analysis of toxin genes from multiple N. vectensis populations and 2 other anemone species, Anemonia viridis and Actinia equina, we observed that the toxin genes for each sea anemone species are more similar to one another than to those of other species, suggesting they evolved by manner of concerted evolution. Furthermore, in 2 of the species (A. viridis and A. equina) we found genes that evolved under diversifying selection, suggesting that concerted evolution and accelerated evolution may occur simultaneously.

Key Words: sea anemone toxins • concerted evolution • Nematostella vectensis

1 Present address: Biology Department, Woods Hole Oceanographic Institution.

Dan Graur, Associate Editor


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