RNA-seq and high-definition mass spectrometry reveal the complex and divergent venoms of two rear-fanged colubrid snakes.

James J Mcgivern,Mark J Margres,Darin R Rokyta,Michelle E Couch,Stephen P Mackessy,Kenneth P Wray

doi:10.1186/1471-2164-15-1061

James J Mcgivern, Mark J Margres + Show 4 more

Open Access

https://doi.org/10.1186/1471-2164-15-1061

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Abstract

BackgroundLargely because of their direct, negative impacts on human health, the venoms of front-fanged snakes of the families Viperidae and Elapidae have been extensively characterized proteomically, transcriptomically, and pharmacologically. However, relatively little is known about the molecular complexity and evolution of the venoms of rear-fanged colubrid snakes, which are, with a few notable exceptions, regarded as harmless to humans. Many of these snakes have venoms with major effects on their preferred prey, and their venoms are probably as critical to their survival as those of front-fanged elapids and viperids.ResultsWe sequenced the venom-gland transcriptomes from a specimen of Hypsiglena (Desert Night Snake; family Colubridae, subfamily Dipsadinae) and of Boiga irregularis (Brown Treesnake; family Colubridae, subfamily Colubrinae) and verified the transcriptomic results proteomically by means of high-definition mass spectrometry. We identified nearly 3,000 nontoxin genes for each species. For B. irregularis, we found 108 putative toxin transcripts in 46 clusters with <1% nucleotide divergence, and for Hypsiglena we identified 79 toxin sequences that were grouped into 33 clusters. Comparisons of the venoms revealed divergent venom types, with Hypsiglena possessing a viper-like venom dominated by metalloproteinases, and B. irregularis having a more elapid-like venom, consisting primarily of three-finger toxins.ConclusionsDespite the difficulty of procuring venom from rear-fanged species, we were able to complete all analyses from a single specimen of each species without pooling venom samples or glands, demonstrating the power of high-definition transcriptomic and proteomic approaches. We found a high level of divergence in the venom types of two colubrids. These two venoms reflected the hemorrhagic/neurotoxic venom dichotomy that broadly characterizes the difference in venom strategies between elapids and viperids.

Highlights

Because of their direct, negative impacts on human health, the venoms of front-fanged snakes of the families Viperidae and Elapidae have been extensively characterized proteomically, transcriptomically, and pharmacologically
Three-finger toxins have been described for colubrids [6,39,40,45], but our results show that colubrid venoms can be as diverse and specialized for 3FTxs as the venoms of elapids
We found clear evidence for positive selection in the cysteine-rich secretory protein (CRISP) (Figure 3), Snake venom metalloproteinase (SVMP), and at least some C-type lectin (CTL) and 3FTxs (Figure 3 and Tables 5, 6, and 7)

Summary

Introduction

Because of their direct, negative impacts on human health, the venoms of front-fanged snakes of the families Viperidae and Elapidae have been extensively characterized proteomically, transcriptomically, and pharmacologically. The genus ranges over a variety of habitats throughout much of western North America, from central Mexico northward throughout the drier regions of the western United States and extreme south-central British Columbia Members of this genus are largely nocturnal and consume prey as diverse as insect, frogs, and snakes, but more than 70% of their diet consists of lizards and squamate eggs [21]. The genus Boiga (subfamily Colubrinae) consists of 33 species of long, slender-bodied, arboreal rear-fanged venomous snakes This nocturnal genus ranges over a variety of habitats across India, southeastern Asia, and northern Australia and is typified by the Brown Treesnake (Boiga irregularis). Birds, and frogs, but more than 60% of its diet consists of lizards and their eggs [23]

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