The regulation of salt and water balance, or osmoregulation, is fundamental to the proper function of the molecules that carry on the business of life in living organisms. This project addresses the gap in knowledge of how osmotic balance is monitored and how an organism responds to any deviation from the optimal state. Detection of a change in this critical balance by osmoreceptor cells is the first step in activating the mechanisms which ensure osmotic balance is restored and maintained. Nevertheless, our understanding of how osmoreceptor cells work has been hindered by their complex structure and arrangement among other cells in the brain, kidney and other organs. This makes it extremely difficult to develop useful experimental approaches. The prolactin cell of the tilapia solves this problem. Prolactin is an osmoregulatory hormone in tilapia, a remarkable fish that can live in fresh water and in salinities exceeding that of seawater. Unlike mammals, prolactin cells in tilapia are arranged into a nearly homogeneous mass in the pituitary gland making it easy to study how the cell is regulated. Prolactin cells have been shown to function as osmoreceptors that respond directly to osmotic changes by altering prolactin secretion which restores osmotic balance. An increase in cell size is the trigger that activates cell mechanisms that increase prolactin secretion. This project will investigate how cell size controls the activity/expression of the gene that encodes prolactin. It is anticipated that this work will increase the fundamental understanding of how osmoreceptor cells work in an economically important food fish grown in fresh water and seawater.

This project will allow the recruitment, education, and training of high school, undergraduate and graduate students, including those of under-represented minorities from within our multi-ethnic, culturally diverse, University and area schools. Progress will be conveyed via institutional educational programs and will be posted on a publically accessible website:

National Science Foundation (NSF)
Division of Integrative Organismal Systems (IOS)
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Steven Ellis
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University of Hawaii
United States
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