title: Testing the Toxicofera: comparative transcriptomics casts doubt on the single, early evolution of the reptile venom system.
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.
authors.affiliation: School of Biological Sciences, Bangor University, Brambell Building, Deiniol Road, Bangor, Gwynedd LL57 2UW, United Kingdom. Electronic address: adamdhargreaves@gmail.com.
authors.forename: Adam D
authors.initials: AD
authors.lastname: Hargreaves
authors.affiliation: Institute of Biological, Environmental & Rural Sciences, Aberystwyth University, Penglais, Aberystwyth, Ceredigion SY23 3DA, United Kingdom. Electronic address: mts11@aber.ac.uk.
authors.forename: Martin T
authors.initials: MT
authors.lastname: Swain
authors.affiliation: Wellcome Trust Sanger Institute, Hinxton, Cambridge CB10 1HH, United Kingdom. Electronic address: dl5@sanger.ac.uk.
authors.forename: Darren W
authors.initials: DW
authors.lastname: Logan
authors.affiliation: School of Biological Sciences, Bangor University, Brambell Building, Deiniol Road, Bangor, Gwynedd LL57 2UW, United Kingdom. Electronic address: j.mulley@bangor.ac.uk.
authors.forename: John F
authors.initials: JF
authors.lastname: Mulley
mesh_terms: D000818:Animals; D001483:Base Sequence; D005075:Biological Evolution; D003545:Cysteine / Q000031:analogs & derivatives / Q000235:genetics; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases / Q000235:genetics; D020869:Gene Expression Profiling / Q000379:methods*; D006821:Hyaluronoglucosaminidase / Q000235:genetics / Q000378:metabolism; D037102:Lectins / Q000235:genetics / Q000378:metabolism; D016013:Likelihood Functions; D008116:Lizards / Q000235:genetics* / Q000378:metabolism*; D008957:Models, Genetic; D008969:Molecular Sequence Data; D010802:Phylogeny; D017423:Sequence Analysis, RNA; D059467:Transcriptome / Q000235:genetics*; D014688:Venoms / Q000235:genetics*; D000097604:Ficolins
chemical_list: D003545:Cysteine; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases; D006821:Hyaluronoglucosaminidase; D037102:Lectins; D014688:Venoms; D000097604:Ficolins; C031752:ethyl cysteine
keywords: Snake venom; Toxicofera; Transcriptomics