Cnidarians such as hydrae and sea anemones are sessile, predatory, soft bodied animals which depend on offensive and defensive allomones for prey capture and survival. These allomones are distributed throughout the entire organism both in specialized stinging cells (nematocytes) and in the body tissues. The cnidarian allomonal system is composed of neurotoxins, cytolysins and toxic phospholipapses. The present bioinformatic survey was motivated by the fact that while hydrae are the most studied model cnidarian, little is known about their allomones. A large-scale EST database from Hydra magnipapillata was searched for orthologs of known cnidarian allomones, as well as for allomones found in other venomous organisms. We show that the hydrae express orthologs of cnidarian phospholipase A2 toxins and cytolysins belonging to the actinoporin family, but could not find orthologs of the 'classic' short chain neurotoxins affecting sodium and potassium conductance. Hydrae also express proteins similar to elapid-like phospholipases, CRISP proteins, Prokineticin-like polypeptides and toxic deoxyribonucleases. Our results illustrate a high level of complexity in the hydra allomonal system, suggest that several toxins represent a basal component of all cnidarian allomones, and raise the intriguing possibility that similar proteins may fulfill both endogenous and allomonal roles in cnidaria.
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We would like to thank the many biologists and bioinformaticists at the University of California, Irvine, Pomona College, and the EST Group of the Genome Sequencing Center (GSC) at Washington University in St. Louis, Missouri, who are involved in the hydra EST database. We would like to thank N. Sher for critical reading of the manuscript. This work is supported by grants 476/01 and 750/04 from the Israel Science Foundation.