探討鹹水模式魚種－恆河青鱂魚（Oryzias dancena）FXYD蛋白質的表現及可能角色

Abstract

FXYD proteins are novel regulators of Na+-K+-ATPase (NKA). In fish subjected to salinity challenges, NKA in osmoregulatory organs (i.e., gills, kidneys, and intestines) is a primary driving force for many ion transport systems that act in concert to maintain a stable internal environment. Although teleostean FXYD proteins have been identified and investigated, previous studies focused on limited species. Based on their close phylogenetic relationships and diverse characteristics, the Oryzias species offer unique models for comparative and osmoregulatory studies. Among them, the brackish medaka (O. dancena) and the Japanese medaka (O. latipes) were model fish commonly used in experiments of different fields. The purposes of the present study were to use the brackish medaka, a saltwater fish model, for illustrating the potential roles of FXYD proteins and to investigate the diversity of teleostean FXYD expression profiles in these two closely related euryhaline medaka upon exposure to salinity changes. Seven members of the FXYD protein family were identified in each medaka species (OdFXYD and OlFXYD). In the osmoregulayory organs, most fxyd genes expressed, and certain fxyd expression was salinity-dependent. Among the cloned genes, fxyd11 and fxyd12 was expressed mainly and abundantly in the gills, kidneys, and intestines, respectively. In gills of the brackish medaka, the OdFXYD11 protein interacted with the NKA α-subunit which was expressed at a higher level in freshwater-acclimated individuals relative to fish in the other salinity groups. Salinity changes led to different effects on the OdFXYD11 and NKA α-subunit expression patterns in the gills of the brackish medaka. This finding (non-correlated expression patterns) is the first report of teleost FXYD proteins in a chronic (i.e., acclimated) rather than an acute (i.e., time-course) salinity challenge experiment. On the other hand, the function of OdFXYD12 was demonstrated to be able to maintain a high-level NKA activity. To our knowledge, this is the first study to illustrate the functions of teleost FXYD12 protein. Taken together, the present study inferred that the FXYD11 might play a crucial role in gills via increasing NKA activity in response to salinity challenge and revealed that FXYD12 was involved in osmoregulation/ionoregulation of internal osmoregulatory organs (i.e., kidneys and intestines) via enhancing NKA activity.