Master of Science (MSc)
Faculty of Science
Dr. Allison McDonald
In addition to the typical electron transport system in animal mitochondria responsible for oxidative phosphorylation, some species possess an alternative oxidase (AOX) pathway, which causes electrons to bypass proton pumping complexes. Although AOX appears to be energetically wasteful, studies have revealed its wide taxonomic distribution, and indicate it plays a role in environmental stress tolerance. AOX discovery in animals is recent, and further research into its expression, regulation, and physiological role has been impeded by the lack of an experimental model organism. DNA database searches using bioinformatics revealed an AOX sequence present in the arthropod Tigriopus californicus. Multiple sequence alignments compared known AOX proteins to that of T. californicus and examined the conservation of amino acid residues involved in AOX catalytic function and post-translational regulation. The physiological function of a native AOX has never been identified in an animal that produces it, but I hypothesize that AOX protein levels will change in response to environmental stress in T. californicus. In order to test this hypothesis, copepods were exposed to five different temperatures (6, 10, 15, 22 and 28°C), and extended periods of light/dark. Samples were taken after 24 hours (acute) and 1 week (chronic) of incubation at each stress treatment. In conclusion, T. californicus possesses the necessary residues required for AOX function. Furthermore, Western blots demonstrate that there are fluctuations in AOX expression when exposing T. californicus to temperature stress. In contrast, during light stress AOX is constitutively expressed when animals were subjected to changes in their circadian rhythms. AOX has been most thoroughly characterized in a number of plants; however, the physiological function of a native AOX has never been identified in an animal that produces it. This is the second study to confirm AOX protein expression in an animal and is the first study to look at a native AOX protein in an animal and its response to biotic stress. By understanding why T. californicus possesses AOX, we can better understand why some other organisms, including humans, do not express or have lost the AOX gene. More thorough investigation of AOX in copepods may aid in the development of a drug that can be added to fish aquaculture to exterminate parasitic copepods and prevent the loss of economically valuable fish.
Tward, Carly, "Expression of alternative oxidase in the copepod T. californicus when exposed to environmental stressors" (2019). Theses and Dissertations (Comprehensive). 2164.