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Platypus Special/Letter

Defensins and the convergent evolution of platypus and reptile venom genes

¹ Faculty of Veterinary Science, University of Sydney, Sydney, New South Wales 2006, Australia; ² Bioinformatics Division, The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3050, Australia; ³ School of Molecular and Microbial Biosciences, University of Sydney, Sydney, New South Wales 2006, Australia; ⁴ Nanoscale Organisation and Dynamics Group, College of Health and Science, University of Western Sydney, Sydney, New South Wales 1797, Australia; ⁵ Australian Research Council (ARC) Centre for Kangaroo Genomics, Research School of Biological Sciences, The Australian National University, Canberra, Australian Capital Territory 0200 Australia; ⁶ Genome Sequencing Center, Washington University School of Medicine, St. Louis, Missouri 63108, USA; ⁷ Department of Human Physiology, Anatomy and Genetics, Medical Research Council (MRC) Functional Genetics Unit, University of Oxford, Oxford OX1 3QX, United Kingdom; ⁸ Centre for Reproduction and Development, Monash Institute of Medical Research, Clayton, Victoria 3168 Australia; ⁹ Department of Zoology, University of Melbourne, Parkville, Victoria 3010 Australia

When the platypus (Ornithorhynchus anatinus) was first discovered, it was thought to be a taxidermist’s hoax, as it has a blend of mammalian and reptilian features. It is a most remarkable mammal, not only because it lays eggs but also because it is venomous. Rather than delivering venom through a bite, as do snakes and shrews, male platypuses have venomous spurs on each hind leg. The platypus genome sequence provides a unique opportunity to unravel the evolutionary history of many of these interesting features. While searching the platypus genome for the sequences of antimicrobial defensin genes, we identified three Ornithorhynchus venom defensin-like peptide (OvDLP) genes, which produce the major components of platypus venom. We show that gene duplication and subsequent functional diversification of beta-defensins gave rise to these platypus OvDLPs. The OvDLP genes are located adjacent to the beta-defensins and share similar gene organization and peptide structures. Intriguingly, some species of snakes and lizards also produce venoms containing similar molecules called crotamines and crotamine-like peptides. This led us to trace the evolutionary origins of other components of platypus and reptile venom. Here we show that several venom components have evolved separately in the platypus and reptiles. Convergent evolution has repeatedly selected genes coding for proteins containing specific structural motifs as templates for venom molecules.

E-mail kbelov{at}vetsci.usyd.edu.au; fax 61-2-9351-3957.

[Supplemental material is available online at www.genome.org.]

Article published online before print. Article and publication date are at http://www.genome.org/cgi/doi/10.1101/gr.7149808.

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