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The innate immune repertoire in Cnidaria - ancestral complexity and stochastic gene loss

David J Miller1, Georg Hemmrich2, Eldon E Ball3, David C Hayward3, Konstantin Khalturin2, Noriko Funayama4, Kiyokazu Agata4 and Thomas CG Bosch2*

Author Affiliations

1 ARC Centre of Excellence in Coral Reef Studies and Comparative Genomics Centre, James Cook University, Townsville, Queensland 4811, Australia

2 Zoological Institute, Christian-Albrechts-University Kiel, Olshausenstrasse, 24098 Kiel, Germany

3 ARC Centre for the Molecular Genetics of Development, Research School of Biological Sciences, Australian National University, Canberra ACT 2601, Australia

4 Department of Biophysics, Kyoto University, Kitashirakawa-Oiwake, Sakyo-ku, Kyoto 606-8502, Japan

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Genome Biology 2007, 8:R59  doi:10.1186/gb-2007-8-4-r59

Published: 16 April 2007

Abstract

Background

Characterization of the innate immune repertoire of extant cnidarians is of both fundamental and applied interest - it not only provides insights into the basic immunological 'tool kit' of the common ancestor of all animals, but is also likely to be important in understanding the global decline of coral reefs that is presently occurring. Recently, whole genome sequences became available for two cnidarians, Hydra magnipapillata and Nematostella vectensis, and large expressed sequence tag (EST) datasets are available for these and for the coral Acropora millepora.

Results

To better understand the basis of innate immunity in cnidarians, we scanned the available EST and genomic resources for some of the key components of the vertebrate innate immune repertoire, focusing on the Toll/Toll-like receptor (TLR) and complement pathways. A canonical Toll/TLR pathway is present in representatives of the basal cnidarian class Anthozoa, but neither a classic Toll/TLR receptor nor a conventional nuclear factor (NF)-κB could be identified in the anthozoan Hydra. Moreover, the detection of complement C3 and several membrane attack complex/perforin domain (MAC/PF) proteins suggests that a prototypic complement effector pathway may exist in anthozoans, but not in hydrozoans. Together with data for several other gene families, this implies that Hydra may have undergone substantial secondary gene loss during evolution. Such losses are not confined to Hydra, however, and at least one MAC/PF gene appears to have been lost from Nematostella.

Conclusion

Consideration of these patterns of gene distribution underscores the likely significance of gene loss during animal evolution whilst indicating ancient origins for many components of the vertebrate innate immune system.