The advanced snakes (superfamily Colubroidea) consist of a monophyletic group of four families: Atractaspididae, "Colubridae", Elapidae and Viperidae [1
]. These snakes have evolved biochemical weapon (toxins), rather than mechanical means of handling prey. Phylogenetic studies show that the venom gland (where toxins are produced) evolved once at the base of the Colubroidea about 60–80 million years ago and has undergone extensive "evolutionary tinkering" of delivery systems and compositions of venom [2
]. Phylogenetic reconstruction between toxin genes and snake families showed that the recruitment of toxin families into the venom gland has occurred multiple times by both basal (e.g. metalloproteinases, CRISP, Kunitz-type serine protease inhibitors, NGF) and independent (e.g. PLA2
, natriuretic peptides) recruitment events [4
]. Approximately 26 families of toxins have been catalogued in snake venom proteomes, and several families appear to be specific to a particular family of venomous snakes (Additional file 1
). Sarafotoxins are found only in venoms of Atractaspididae; serine proteinases related to blood coagulation factors Xa, cobra venom factor, waprins and AVIT (prokineticin) family peptides appear to be limited to the Elapidae; and vascular endothelial growth factor (VEGF), disintegrins, waglerins, dipeptidyl peptidase IV and crotamine occur primarily in venoms of the Viperidae (Additional file 1
). The occurrence, relative abundance and pharmacological potency of various members of these toxin families in venom make envenomation remarkably complex. Envenomation by elapid snakes is usually characterized by rapid neurotoxic complications due to presence of large amounts of postsynaptic neurotoxins [5
], while envenomation by viperid snakes evokes complex hemorrhagic, hypotensive and inflammatory effects caused by the actions of numerous serine proteinases, metalloproteinases and C-type lectins (CLP) [6
]. Effects of envenomation by snakes in the genus Atractaspis
can include vasoconstriction, resulting in cardiac arrest [10
]. Despite overall similarity in clinical symptoms exhibited after envenomation by members of a particular family of snakes, there exists considerable species-specific variation in absolute effects within each group, contributing to the difficulty in assessing and treating envenomated victims.
Previously, identification and characterization of venom components relied primarily on various methods in protein chemistry or on cloning of individual genes. However, neither approach is well-suited to detect toxins that are found in low abundance. Therefore, the apparent absence of a particular family of toxins from venom could be due either to their very low abundance or to the lack of expression in the venom gland. The genes of low abundance toxins are best discovered by the construction of a cDNA library and sequencing of a sizeable number of ESTs. Using this approach, new toxin genes in known families as well as several completely new families of toxins have been discovered, and the spectrum of snake toxin proteome is gradually expanding [11
]. To search for novel and low abundance toxin genes or new families of toxins, we constructed a cDNA library and sequenced ESTs from the venom gland of Sistrurus catenatus edwardsii
(Massasauga Rattlesnake) is a small pitviper broadly distributed across the North American prairies from Ontario, Canada and New York to extreme southeastern Arizona, with an apparently disjunct population in northern Chihuahua, Mexico [29
]. One subspecies, S. c. edwardsii
(Desert Massasauga), occurs primarily in arid and desert grasslands, occasionally occurring in dune formations and desert scrub [31
]. Populations of S. catenatus
generally are threatened or declining rangewide, primarily as a result of habitat loss and human encroachment, and therefore endangered species status has been recommended [34
]. In a systematic study, Holycross and Mackessy [33
] showed that among Colorado, Arizona and New Mexico populations of S. c. edwardsii
, lizards are the major prey, followed by small mammals and centipedes. In the present work, the venom gland has been collected from snakes originating from the Colorado population.
General symptoms of envenomation resulting from many North American pitvipers bite are pain, local tissue effects (progressive edema, erythema and necrosis) with coagulopathy (hypofibrinogenemia and prolongation of prothrombin time) and thrombocytopenia as systemic effects. However, there is no specific report to date in the literature concerning envenomation by S. c. edwardsii. Profiling of toxin expression of this threatened snake species will give a global view for the expression of all genres of toxins, including variation in coding/noncoding sequences and their evolutionary trends. The results of this study will also help in the understanding of envenomation processes of rattlesnake bites, which in turn will be important for more effective clinical treatment and antivenom management in cases of snakebite.