Testing the Toxicofera: Comparative transcriptomics casts doubt on the single, early evolution of the reptile venom system

Adam Hargreaves, Martin Thomas Swain, Logan Darren, Mulley John

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Abstract

The identification of apparently conserved gene complements in the venom and salivary glands of a diverse set of reptiles led to the development of the Toxicofera hypothesis – the single, early evolution of the venom system in reptiles. However, this hypothesis is based largely on relatively small scale EST-based studies of only venom or salivary glands and toxic effects have been assigned to only some putative Toxicoferan toxins in some species. We set out to examine the distribution of these proposed venom toxin transcripts in order to investigate to what extent conservation of gene complements may reflect a bias in previous sampling efforts. Our quantitative transcriptomic analyses of venom and salivary glands and other body tissues in five species of reptile, together with the use of available RNA-Seq datasets for additional species, shows that the majority of genes used to support the establishment and expansion of the Toxicofera are in fact expressed in multiple body tissues and most likely represent general maintenance or “housekeeping” genes. The apparent conservation of gene complements across the Toxicofera therefore reflects an artefact of incomplete tissue sampling. We therefore conclude that venom has evolved multiple times in reptiles.
Original languageEnglish
Pages (from-to)140-156
Number of pages17
JournalToxicon
Volume92
Issue numberN/A
Early online date17 Oct 2014
DOIs
Publication statusPublished - 15 Dec 2014

Keywords

  • Snake venom
  • Transcriptome
  • Toxicofera

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