Elizabeth Sears
Education
M.Sc. Candidate, Department of Integrative Biology, University of Guelph
B.Sc. Hons. Biological Sciences, Marine and Freshwater Biology, University of Guelph
Research
Graduate:
I am interested in the evolution of the vertebrate heart and the diversity, both structurally and functionally, seen across phyla. My research focuses on the troponin protein complex, and the structural and functional changes found in the evolution of endothermy. Changes in amino acid sequence of this complex are at least partially responsible for differences in calcium sensitivity and adrenergic sensitivity between ectotherms (such as teleost fish) and endotherms (such as mammals). Generally speaking, ectothermic hearts have a much higher calcium sensitivity than endotherms, allowing them to function at low temperatures which would be fatal to mammals. Endotherms on the other hand have a lower calcium sensitivity, enabling the contractile element to remain responsive to calcium activation at high temperatures. I am interested in how key changes in contractile protein function may be linked to the evolution of endothermy in vertebrates.
I will be investigating the functional characteristics of the cardiac troponin complex from the African clawed frog (Xenopus laevis), and comparing it to troponin complex function of the rat and the rainbow trout. As an amphibian, the clawed frog is an ectotherm, but resides at temperatures between 15 and 30 degrees C, making them an excellent intermediate study system between cold adapted ectotherms, and endotherms.
Undergraduate:
Changes in troponin isoform expression have been observed during development in many organisms, including chicken and mice. Embryonic forms of troponin T (TnT) and troponin I (TnI) in the cardiac muscle of these organisms more closely resemble the adult forms of slow skeletal TnT and TnI than the adult cardiac forms. It has been suggested that this is due to the fact that slow skeletal troponins are less sensitive to acidosis than the cardiac isoforms. My undergraduate research investigated different aspects of troponin expression in developing rainbow trout (Oncorhynchus mykiss) hearts. In continued studies, we hope to determine whether different isoforms of cardiac TnT and TnI are expressed during development, and what stage is critical to switching of the isoforms. This could give us an indication of different cardiac contractile needs at different developmental stages.
My undergraduate work also investigated the effect of the drug isoproterenol on the heart tissue of developing rainbow trout embryos. Isoproterenol is a beta-agonist, which acts to stimulate beta-receptors, resulting in increased heart rate and vasodilation. This cardiac stimulant acts by increasing adenylyl cyclase activity, which could cause differences in phosphorylation of contractile proteins, including the troponin complex. I looked at the effect of isoproterenol on the phosphorylation state of the troponin subunits at different stages of embryonic and larval development.
esears@uoguelph.ca