Salt and water balance is a basic requirement for most vertebrates to keep separate internal chemical conditions, irrespective of external influence. Therefore, the physiology of transport epithelia is fundamental to vertebrate life and the impairment of function is involved in many health problems. In fish, the gill, gut, and kidney perform the homeostatic regulation of water and salt transport. Euryhaline fish species like trout can move between diverse salinities and this requires a unique functional plasticity in these organs, which in turn makes them ideal models in the study of epithelial physiology. The proposed research will use the trout gill model to study tight junction proteins of the claudin family. These proteins are essential for regulation of epithelial permeability. The overall goal of the research is to comprehend the regulation and specific function of claudin proteins. We will provide new insights into basic physiological mechanisms, which ultimately will enhance our understanding of related pathological conditions in fish as well as in higher vertebrates. Our current data suggests that claudin-10e is involved in sodium secretion in seawater fish and possibly subject to rapid regulation, while claudin-28a is a target for prolactin induced freshwater acclimation. Accordingly, the aims of the project are to test the following hypotheses: i) the secretion path for sodium in the gill of seawater trout is primarily defined by the presence of claudin-10e, ii) phosphorylation of gill claudin-10e is involved in the control of gill permeability and is critical during seawater-acclimation, iii) prolactin-induced tightening of the gill epithelium during freshwater acclimation is mostly dependent on claudin-28a expression. The project is designed to demonstrate key principles of tight junction remodeling in the gill of euryhaline fishes and to explain how rapid onset/offset of sodium secretion may be controlled. Multidisciplinary methods will be applied, ranging from analysis of transcript and protein expression, tissue localization, and electrophysiological studies of monolayered cell cultures. These methods will complement each other and are ideal for gaining novel molecular insight into basic biological mechanisms. During the project several undergraduate, two graduate students and one postdoctoral fellow will gain a broad training in vertebrate biology and biochemical, molecular and physiological methods. Outreach include, a partnership with the George Washington Carver research program that provides summer research experiences for undergraduates from Historically Black Colleges and Universities and Hispanic serving institutions. The broader scientific impact of the proposed research relates to potential health applications based on the increased understanding at the molecular level of water and salt management in vertebrates along with applications in the biotechnology and aquaculture industry. The project will also contribute to the development of research resources and capacity in Arkansas, an EPSCoR jurisdiction.
