Background: To date, few peptides in the complex mixture of platypus venom have been identified andsequenced, in part due to the limited amounts of platypus venom available to study. We have constructed andsequenced a cDNA library from an active platypus venom gland to identify the remaining components. Results: We identified 83 novel putative platypus venom genes from 13 toxin families, which are homologous toknown toxins from a wide range of vertebrates (fish, reptiles, insectivores) and invertebrates (spiders, seaanemones, starfish). A number of these are expressed in tissues other than the venom gland, and at least three ofthese families (those with homology to toxins from distant invertebrates) may play non-toxin roles. Thus, furtherfunctional testing is required to confirm venom activity. However, the presence of similar putative toxins in suchwidely divergent species provides further evidence for the hypothesis that there are certain protein families thatare selected preferentially during evolution to become venom peptides. We have also used homology with knownproteins to speculate on the contributions of each venom component to the symptoms of platypusenvenomation. Conclusions: This study represents a step towards fully characterizing the first mammal venom transcriptome. Wehave found similarities between putative platypus toxins and those of a number of unrelated species, providinginsight into the evolution of mammalian venom.
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