Mackessy, Stephen P.
Keenan, Susan M.
University of Northern Colorado
Type of Resources
Place of Publication
University of Northern Colorado
For decades, snakes and snake venoms have been utilized in numerous aspects of biological and biomedical research. Behaviorally, snakes have been examined for their extraordinary chemosensory capabilities, providing a detailed understanding of their foraging ecology and predatory responses. The presence of a highly complex vomeronasal organ has enabled snakes to not only respond to, but also discriminate between a high-range of heterospecific, conspecific, predatory, and prey-derived chemical odors. Snake venom has allowed for a transition in predatory behaviors, and this often complex mixture of proteins and peptides has provided researchers with an ever growing catalog of natural compounds that may be applicable as novel therapeutics or as biomedical reagents. Research into venomous systems also provides a detailed understanding of the biological roles of venom compounds, as well as providing critical information necessary for the proper assessment and treatment of snakebite. The current work addresses several aspects of snake behavior and snake venom toxinology and has four major objectives: i) to examine the chemosensory responses of neonate, subadult and adult Prairie Rattlesnake (Crotalus viridis viridis) to various prey chemical stimuli, ii) to identify the chemical component(s) of venom which allows for prey recovery during viperid predatory episodes, iii) to examine the anti-cancer effects of a novel snake venom disintegrin towards various human derived cancer cell lines and iv) to complete in-depth proteomic analyses of the neonate and adult C. v. viridis and examine the efficacy of the current anti-venom treatment CroFab® against this species’ venom. Chapter I presents the objectives and aims of my dissertation work, and provides background on chemosensory systems in squamates, and the numerous studies examining prey relocation in viperid snakes. Further, this chapter addresses the importance of examining the potential medicinal values of disintegrins as anti-cancer therapeutics, and the utilization of proteomics to develop a better understanding of venom composition and anti-venom efficacy. Chapters II focuses on the chemosensory responses of wild-caught neonate, subadult, and adult C. v. viridis to natural and non-natural prey-derived chemical odors. Results indicate that responses to chemical stimuli shift with snake age, correlating with ontogenetic changes in snake diet. Chapter III examines this phenomenon in more detail with a group of “stunted”C. v. viridis which had been in captivity since birth and had only consumed neonate lab mice (Mus musculus). Further, these snakes were the age of adults yet only the size of large juveniles, therefore they could not consume larger prey normally taken by adult snakes. Results suggest that ontogenetic shifts in responsiveness to natural prey chemical cues are innately programmed and are not based on body size or feeding experience. Chapter IV identifies the venom component, disintegrins, which are responsible for prey recovery during strike-induced chemosensory searching in Western Diamondback Rattlesnakes (Crotalus atrox). In Chapter V, a novel disintegrin protein (named tzabcanin) was isolated from the venom of the Middle American Rattlesnake (Crotalus simus tzabcan) and the cytotoxic and anti-adhesion properties of this protein toward Colo-205 and MCF-7 cell lines was examined. Chapter VI also examines the anti-cancer effects of tzabcanin towards A-375 and A-549 cell lines, and by specifically binding integrin ανβ3, tzabcanin inhibits cell migration and cell adhesion to vitronectin. In Chapter VII, a detailed proteomic analysis of the venoms of four individual C. v. viridis is presented, showing a novel trend in ontogenetic changes in venom composition, as well as identifying which compounds are, and which are not, effectively immunocaptured by the current anti-venom therapy used in the United States, CroFab®.
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