Elazar Kochva

Early evolution of the venom system in lizards and snakes

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). Evolution of the venom system is thought to underlie the impressive radiation of the advanced snakes (2,500 of 3,000 snake species). 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. 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.

Sarafotoxins S6: several isotoxins from Atractaspis engaddensis (burrowing asp) venom that affect the heart.

Three isotoxins, named sarafotoxins S6a1, S6b and S6c, with strong cardiotoxic activity were isolated from the venom of a snake, Atractaspis engaddensis. All three sarafotoxins are homologous peptides (four or less than four residue replacements) consisting of 21 amino acid residues. Their structure and activity are novel among snake venom components.

Evolutionary origin and development of snake fangs

Many advanced snakes use fangs—specialized teeth associated with a venom gland—to introduce venom into prey or attacker. Various front- and rear-fanged groups are recognized, according to whether their fangs are positioned anterior (for example cobras and vipers) or posterior (for example grass snakes) in the upper jaw. A fundamental controversy in snake evolution is whether or not front and rear fangs share the same evolutionary and developmental origin. Resolving this controversy could identify a major evolutionary transition underlying the massive radiation of advanced snakes, and the associated developmental events. Here we examine this issue by visualizing the tooth-forming epithelium in the upper jaw of 96 snake embryos, covering eight species. We use the sonic hedgehog gene as a marker, and three-dimensionally reconstruct the development in 41 of the embryos. We show that front fangs develop from the posterior end of the upper jaw, and are strikingly similar in morphogenesis to rear fangs. This is consistent with their being homologous. In front-fanged snakes, the anterior part of the upper jaw lacks sonic hedgehog expression, and ontogenetic allometry displaces the fang from its posterior developmental origin to its adult front position—consistent with an ancestral posterior position of the front fang. In rear-fanged snakes, the fangs develop from an independent posterior dental lamina and retain their posterior position. In light of our findings, we put forward a new model for the evolution of snake fangs: a posterior subregion of the tooth-forming epithelium became developmentally uncoupled from the remaining dentition, which allowed the posterior teeth to evolve independently and in close association with the venom gland, becoming highly modified in different lineages. This developmental event could have facilitated the massive radiation of advanced snakes in the Cenozoic era, resulting in the spectacular diversity of snakes seen today.

Neutralization of Viperidae and Elapidae snake venoms by sera of different animals

The venoms of three vipers, Vipera palaestinae, Echis colorata and Pseudocerastes fieldi, and the elapid Walterinnesia aegyptia, all from Israel, show a similar ld50 of 250–300 μg/kg body weight when injected intravenously into mice. The venoms of the viperid Aspis cerastes from Israel and the elapid Naja nigricollis from East Africa are less toxic and have an ld50 of 600 and 1200 μg/kg respectively. Compared with mice on a weight basis, V. palaestinae, Natrix tessellata (a non-venomous water snake) and the mammal Herpestes ichneumon (mongoose) are highly resistant to V. palaestinae venom; Mesocricetus auratus (hamster) also shows some degree of tolerance. The sera from these and other animals were tested for their capacity to neutralize this venom in vitro. The snake sera, which represented the families Elapidae, Viperidae, Crotalidae and Colubridae, all neutralized V. palaestinae venom, whereas sera from two lizards (Uromastix aegyptius and Agama stellio) failed to do so. Of the mammalian sera tested, neutralization was clearly demonstrated with hamster serum and to a lesser degree with hedgehog (Erinaceus europeus) serum, but not with human serum, cat serum or rabbit serum, and even serum from the highly resistant mongoose failed to show any neutralization. In tests involving these sera and the 6 venoms listed above, the Viperidae venoms were neutralized by sera from snakes of the same family, by W. aegyptia serum, and, with the exception of E. colorata venom, by N. nigricollis serum. The neutralization by sera from non-venomous snakes was slightly less complete, and sera from the mongoose and hamster failed to neutralize in some cases. N. nigricollis venom could be neutralized by the homologous serum and by W. aegyptia serum, but not by any others. All test sera, including the homologous serum, were without effect on W. aegyptia venom. Despite the lack of neutralizing capacity of its serum, W. aegyptia is highly resistant to its own venom and the mongoose to both of the elapid venoms tested. This resistance is apparently not due to humoral factors.

A novel cardiotoxic polypeptide from the venom of Atractaspis engaddensis (burrowing asp): Cardiac effects in mice and isolated rat and human heart preparations

A new cardiotoxic polypeptide isolated from the venom of the snake Atractaspis engaddensis has an LD50 of 15 micrograms/kg body weight in white mice. Intravenous administration in mice of lethal doses of the toxin causes, within seconds, marked changes in the ECG, consisting primarily of a transient slope elevation of the S-T segment, a temporary diminution of the S-wave and an increase in the amplitudes of the R- and T-waves. Concomitantly, and apparently unrelated to these changes, a severe A-V block develops and leads to complete cardiac arrest within a few min. Studies with rat and human isolated heart preparations showed that the toxin exerts a powerful coronary vasoconstriction (rats), and positive inotropic effects (rats and humans).

A new type of toxin in the venom of snakes of the genus Atractaspis (Atractaspidinae).

The venom of Atractaspis is unique in having a large percentage of both high and low molecular weight components. Its Sephadex G-50 S5 fraction appears to represent a new type of toxin that contains 17-18 Asx, 13-14 Cys and 10-11 Glx out of a total of 72-78 amino acids. The N-terminal of this toxin does not seem to resemble any of the known toxins. The overall lethal potency of the venom is very high; i.v. injections of 5 microgram of venom or 1 microgram of fractions S5 or S6 per mouse causes death within minutes. The results of the present study corroborate previous findings that suggested a separate grouping of the snakes genus Atractaspis at the subfamilial or familial level.

SRTX-d, a new native peptide of the endothelin/sarafotoxin family

Sarafotoxin; Endothelin; Snake venom; Aorta

A central role for venom in predation by Varanus komodoensis (Komodo Dragon) and the extinct giant Varanus (Megalania) priscus

The predatory ecology of Varanus komodoensis (Komodo Dragon) has been a subject of long-standing interest and considerable conjecture. Here, we investigate the roles and potential interplay between cranial mechanics, toxic bacteria, and venom. Our analyses point to the presence of a sophisticated combined-arsenal killing apparatus. We find that the lightweight skull is relatively poorly adapted to generate high bite forces but better adapted to resist high pulling loads. We reject the popular notion regarding toxic bacteria utilization. Instead, we demonstrate that the effects of deep wounds inflicted are potentiated through venom with toxic activities including anticoagulation and shock induction. Anatomical comparisons of V. komodoensis with V. (Megalania) priscus fossils suggest that the closely related extinct giant was the largest venomous animal to have ever lived.

Evolution and diversification of the Toxicofera reptile venom system.

The diversification of the reptile venom system has been an area of major research but of great controversy. In this review we examine the historical and modern-day efforts of all aspects of the venom system including dentition, glands and secreted toxins and highlight areas of future research opportunities. We use multidisciplinary techniques, including magnetic resonance imaging of venom glands through to molecular phylogenetic reconstruction of toxin evolutionary history, to illustrate the diversity within this integrated weapons system and map the timing of toxin recruitment events over the toxicoferan organismal evolutionary tree.

Sarafotoxins and endothelins: evolution, structure and function☆

The venom of the burrowing asp Atractaspis engaddensis contains several 21 amino acid residue peptides known as sarafotoxins. The sarafotoxins are homologous to the mammalian endothelin family, and they have similar biological activities. This review covers recent advances in the study of the chemical and biological properties of the sarafotoxins and endothelins.