Cloning and Expression of Guanylin-Like Peptides in Teleost Fish

Euryhaline teleosts migrate between SW environments and FW lakes and rivers at various stages in their life cycle. During such migrations, fish face a number of osmotic challenges. FW is a hypo-osmotic environment which results in an influx of water across permeable body surfaces (predominately the gills). To counteract this effect the fish excrete large volumes of urine and limit their rate of drinking. In contract when the hyperosmotic SW environment, fish lose water and cellular dehydration occurs. To overcome these effects fish drink copious amounts of SW and ions and water are taken up across the intestine by regulated ion and water transporters which control the rate and the amount of solute/water absorption. The absorbed monovalent ions are actively secreted back to the environment by gill chloride cells are the water is retained. A number of neuronal and hormonal mechanisms have been identified in teleosts which act together to control fluid absorption and secretion thus maintaining body fluid homeostasis even at the extremes of environmental salinity. We hypothesise that the 15 amino acid peptide hormone guanylin also contributes to this osmotic regulation. Little is known about the physiological roles of this peptide in species other than a few mammals. Using cloning, sequencing and expression techniques our present data suggests that guanylin-like peptides are present in both stenohaline and euryhaline teleosts and in the European eel we have identified two distinct members of the guanylin family. The effect of FW/SW acclimation in the expression of these genes will be discussed.