Regulation of Energy Balance and Intestinal Function in Ancient Fishes

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Appropriate regulation of energy balance is of fundamental importance to all life on earth and is in part achieved in multi-cellular organisms by a suite of hormones released into the circulatory system that act to control uptake of nutrients across the intestine followed by, distribution, storage or use by the organism. Regulation of blood glucose in humans by insulin released from pancreatic B cells is perhaps the most intensively studied example of this. In the ancient fishes how hormones regulate uptake, storage and/or use of nutrients is largely unexplored. As `living fossils' elasmobranchs (sharks, skates and rays) and sturgeons are excellent models to address the long-term goal of my research program that is, to understand how the function of hormones like insulin and corticosteroids have evolved in vertebrates. There are three primary areas of research with short term objectives aiming to understand: 1) control of hormone release; 2) hormonal regulation of nutrient uptake across the gut; and 3) hormonal control of nutrient processing by the liver. The primary nutrient of interest is glucose; however, metabolic organization in sturgeons and in particular, elasmobranchs, indicate ketones also play an important role in whole animal energy balance. Proposed objectives focus on the regulation of insulin release in the pancreatic islet cells of both elasmobranchs and sturgeon and how glucoregulating hormones such as insulin, glucagon and GLP 1 influence uptake of glucose across the gut in these ancient fishes. The action of cortisol in sturgeon and the elasmobranch specific corticosteroid, 1alpha-hydroxycorticosterone (1 alpha-OHB), on processing of glucose and ketones in the liver in both groups of fishes will further our understanding in the mechanistic underpinnings of the stress response in these fishes. Elasmobranch specific research will examine the role the intestine microbial community plays in whole body nitrogen balance and test the novel hypothesis that through a mutualistic relationship tissue bacteria mediate synthesis of 1alpha-OHB, a steroid that is central to whole body energy and nitrogen balance in this ancient group of fishes. HQP involved in this research will gain technical skills at all levels of whole animal physiology. Studies are designed to discover the evolution of regulatory mechanisms controlling complex physiological systems in an inclusive environment that promotes the success of all individuals through community involvement, conference attendance, collaboration and publication. The research will significantly impact our understanding of the evolution of perhaps the most studied hormones in comparative endocrinology; insulin and corticosteroids. Furthermore, many species of sturgeons and elasmobranchs are under threat of extinction around the world; data generated will be applied to improve management and conservation efforts for elasmobranchs in the global aquarium trade and conservation aquaculture of sturgeons.