Aquaporins are a family of membrane proteins that provide channels for the rapid movement of water molecules and some small solutes across the cellular membrane. Since the discovery of the first water channel protein, hundreds of homologous proteins have been found in all forms of life and much has been learned about their complex role in body water homeostasis. This is the first study to use molecular and immunological techniques to demonstrate that an orthologue of mammalian AQP3 is present in the epithelial cells of Squalus acanthias dogfish shark kidney, gills, rectal gland, esophagus, stomach, eye and brain. The full-length Squalus acanthias sequence has 73.8% amino acid identity to human AQP3. Quantitative PCR experiments suggest that constitutive AQP3 expression in the esophagus and kidney may be regulated by external salinity, but the role of AQP3 in water homeostasis of marine elasmobranchs such as Squalus acanthias is yet to be described
