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Early evolution of the venom system in lizards and snakes

机译：蜥蜴和蛇中毒液系统的早期进化

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Among extant reptiles only two lineages are known to have evolved venom delivery systems, the advanced snakes and helodermatid lizards ( Gila Monster and Beaded Lizard)(1). Evolution of the venom system is thought to underlie the impressive radiation of the advanced snakes ( 2,500 of 3,000 snake species)(2-5). In contrast, the lizard venom system is thought to be restricted to just two species and to have evolved independently from the snake venom system(1). Here we report the presence of venom toxins in two additional lizard lineages ( Monitor Lizards and Iguania) and show that all lineages possessing toxin-secreting oral glands form a clade, demonstrating a single early origin of the venom system in lizards and snakes. Construction of gland complementary-DNA libraries and phylogenetic analysis of transcripts revealed that nine toxin types are shared between lizards and snakes. Toxinological analyses of venom components from the Lace Monitor Varanus varius showed potent effects on blood pressure and clotting ability, bioactivities associated with a rapid loss of consciousness and extensive bleeding in prey. The iguanian lizard Pogona barbata retains characteristics of the ancestral venom system, namely serial, lobular non-compound venom-secreting glands on both the upper and lower jaws, whereas the advanced snakes and anguimorph lizards ( including Monitor Lizards, Gila Monster and Beaded Lizard) have more derived venom systems characterized by the loss of the mandibular ( lower) or maxillary ( upper) glands. Demonstration that the snakes, iguanians and anguimorphs form a single clade provides overwhelming support for a single, early origin of the venom system in lizards and snakes. These results provide new insights into the evolution of the venom system in squamate reptiles and open new avenues for biomedical research and drug design using hitherto unexplored venom proteins.
机译：在现存的爬行动物中，只有两个血统已经进化出了毒液输送系统，即高级蛇和嗜血蜥蜴（吉拉·怪物和串珠蜥蜴）（1）。毒液系统的进化被认为是高级蛇（3,000种蛇中的2500种）令人印象深刻的辐射的基础（2-5）。相比之下，蜥蜴毒液系统仅限于两个物种，并且独立于蛇毒液系统而进化（1）。在这里，我们报告了另外两个蜥蜴谱系（Monitor Lizards和Iguania）中毒毒素的存在，并显示所有具有分泌毒素的口腔腺的谱系都形成了进化枝，证明了蜥蜴和蛇中毒液系统的一个早期起源。腺互补DNA文库的构建和转录本的系统发育分析表明，蜥蜴和蛇之间共有九种毒素类型。对Lace Monitor Varanus varius毒液成分的毒理学分析表明，其对血压和凝血能力，与生物活性迅速丧失意识和猎物大量出血相关的有效作用。鬣蜥蜥蜴Pogona barbata保留了祖先毒液系统的特征，即上颚和下颚上有连续的小叶非复合性分泌毒液的腺体，而高级蛇和anguimorph蜥蜴（包括Monitor Lizards，Gila Monster和Beaded Lizard）有更多衍生的毒液系统，其特征是下颌（下部）或上颌（上部）腺体丧失。证明蛇，鬣蜥和anguimorphs形成单一进化枝，为蜥蜴和蛇中毒液系统的单个早期起源提供了压倒性的支持。这些结果为鳞状爬行动物中毒液系统的进化提供了新见识，并为迄今尚未使用的毒液蛋白的生物医学研究和药物设计开辟了新途径。

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