Shabnam Mohammadi, Ph.D.
I'm a highly integrative biologist that investigates the physiology and molecular mechanisms of specialized adaptive traits in organisms. I am currently at Utah State University, where I recently completed my Ph.D. I completed my master's degree at Old Dominion University on morphological and physiological comparisons of snakes with toxic and non-toxic diets.
Current Research. My current studies aim at elucidating the genetic origins, and the molecular and physiological mechanisms of toxin resistance in snakes. I currently focus on the snake-toad (predator-prey) system.
Genetic origin of bufadienolide resistance
Bufadienolides are toxins used by toads as chemical defense. These steroids carry out their toxic effects by binding to and inhibiting the Na+/K+ATPases of cell membranes. By comparing and testing the sequences of the bufadienolide binding sites of Na+/K+ATPases I am able to determine whether a species is resistant or nonresistant to bufadienolides through the presence/absence of resistance-conferring mutations. I am also able to use these sequences to trace the origins of resistance through ancestral state analyses. See recent work published in Proceedings of the Royal Society B.
Physiological mechanisms of bufadienolides resistance
The physiological mechanisms of bufadienolide resistance have not yet been fully investigated. Bufadienolides have a long history of use in human medicine and most studies have focused on their effects on the heart, where they exert their most pronounced effect in mammals. I am using dose-challenge experiments in living snakes in conjunction with physiological monitoring, including electrocardiography and blood hormone measurements, to investigate the consequences of resistance and to determine whether there are other possible mechanisms involved in resistance (i.e., non-target-site insensitivity mechanisms). (Recent work currently in press in General and Comparative Endocrinology)
Investigations of molecular mechanisms of bufadienolide resistance
To further investigate the mechanisms of resistance in snakes, I use functional in vitro
enzymatic assays and qPCR to measure Na+/K+ATPase activity and expression in various tissues of snakes. The aim of this study is to determine whether variation in resistance occurs between species and within individuals at Extracting steroid hormones from snake blood. the organ level. See recent work published in GENE)
I am interested in taking my research in directions that further dig into the understanding of the gene regulatory pathways of mutant Na+/K+-ATPases and the physiological controls of these pathways. I am also interested in using ancestral state reconstruction and bioengineering of ancient proteins to learn how the Na+/K+-ATPase of snakes has changed over evolutionary time from the bufadienolide-sensitive ancestral state to the bufadienolide-resistant modern state. Not only would this allow us to observe stepwise changes in the DNA sequences but also physiological differences in the enzymes themselves.
In addition to studying the evolution and physiology of predators of toxic prey, my diverse toolbox has allowed me to enter into research collaborations of other study systems involving extreme adaptations. I am currently investigating population-level physiological adaptations to saline environments in amphibians from the Pacific Northwest and Japan. I look forward to continue expanding my collaborations into other systems.