Intestinal FXYD12 and sodium-potassium ATPase: A comparative study on two euryhaline medakas in response to salinity changes

FXYD proteins are the regulators of sodium-potassium ATPase (Na+/K+-ATPase, NKA). In teleosts, NKA is a primary driving force for the operation of many ion transport systems in the osmoregulatory organs (e.g. intestines). Hence, the purpose of this study was to determine the expression of FXYD proteins and NKA α-subunit in the intestines of two closely related medakas (Oryzias dancena and O. latipes), which came from different salinity habitats and have diverse osmoregulatory capabilities, to illustrate the association between NKA and FXYD proteins of two medaka species in response to salinity changes. The results showed that the fxyd12 mRNA was the most predominant in the intestines of both medakas. The association of FXYD12 and NKA in the intestines of the two medaka species was demonstrated via double immunofluorescent staining and co-immunoprecipitation. Upon salinity challenge, the localization of FXYD12 and NKA was similar in the intestines of the two medaka species. However, the expression profiles of intestinal FXYD12 and NKA (mRNA and protein levels), as well as NKA activity differed between the medakas. These results showed that FXYD12 may play a role in modulating NKA activity in the intestines of the two medakas following salinity changes in the maintenance of internal homeostasis. These findings contributed to knowledge of the expression and potential role of vertebrate FXYD12, the regulators of NKA, upon salinity challenge.FXYD蛋白（FXYD proteins）是钠钾ATP酶（Na+/K+-ATPase，NKA）的调控因子。在硬骨鱼类中，NKA是渗透调节器官（如肠道）内多种离子转运系统运作的核心动力来源。因此，本研究旨在探究两种亲缘关系相近的青鳉（尖吻青鳉*Oryzias dancena*与日本青鳉*O. latipes*）肠道中FXYD蛋白与NKA α亚基的表达情况——这两种青鳉栖息于不同盐度生境，渗透调节能力存在差异——以阐明两种青鳉的NKA与FXYD蛋白在应对盐度变化时的关联机制。研究结果显示，fxyd12 mRNA是两种青鳉肠道中表达丰度最高的FXYD家族转录本。通过双重免疫荧光染色与免疫共沉淀实验，证实了两种青鳉肠道内FXYD12与NKA的相互作用关系。在盐度胁迫处理后，两种青鳉肠道内FXYD12与NKA的定位模式保持一致。但二者肠道内FXYD12与NKA的表达谱（mRNA及蛋白水平）以及NKA活性均存在物种差异。上述结果表明，在盐度变化引发的体内稳态维持过程中，FXYD12可能通过调控两种青鳉肠道内的NKA活性发挥功能。本研究结果丰富了脊椎动物FXYD12（NKA的调控因子）在盐度胁迫下的表达模式与潜在功能相关的认知。