The ubiquitous Na, K-ATPase is a membrane-bound ion pump located in the plasma membrane in all animal cells and plays an essential role in a variety of cellular functions. Studies in several organisms have shown that this protein regulates different aspects of embryonic development and is responsible for the pathogenesis of several human diseases. Na, K-ATPase is an important factor for retinal development, and combinations of the isoforms of each of its subunits are expressed in different cell types and determine its functional properties. In this study, we performed RT-PCR assay to determine temporal expression and in situ hybridization to determine spatial expression of Na, K-ATPase β2 isoform (atp1b2) in Xenopus laevis. Focusing on retinal expression to distinguish the specific expression domain, we used retinal marker genes sox4, sox11, vsx1, and pax6. Xenopus atp1b2 was expressed from late gastrulation to the tadpole stage. Using whole mount in situ hybridization, we showed that Xenopus atp1b2 was expressed broadly in the eye, the whole surface ectoderm, and gills. In situ hybridization on sections revealed detailed and specific expression in the outer nuclear layer of the retina, which consists of two major classes of photoreceptors, rods and cones, surface ectoderm, pharyngeal epithelium, and gills. These findings indicate that atp1b2 may play an important role for the development of Xenopus retina.

Na+/K+-ATPase, an energy-transducing ion pump, is responsible for maintenance of relatively high concentrations of potassium ions but low concentrations of sodium ions in the cell by transport of these ions across the plasma membrane. Na+/K+-ATPase consists of α, β, and γ subunits, but only α and β subunits are needed for basic functions. Na+/K+-ATPase is also involved in regulation of intracellular calcium ion concentration by coupling with Na+/Ca2+ exchanger involved in intracellular calcium extrusion. Our previous study showed that calcium regulatory molecules including Na+/Ca2+ exchanger are expressed in the uterine endometrium during the estrous cycle and pregnancy in pigs, however, expression of Na+/K+-ATPase in the uterine endometrium has not been determined. Thus, we examined expression of α1 (ATP1A1) and β1 (ATP1- B1) subunits of Na+/K+-ATPase in the uterine endometrium during the estrous cycle and pregnancy in pigs. Real-time RT-PCR analysis showed that levels of ATP1A1 m- RNA in the uterine endometrium during the estrous cycle and early pregnancy were higher than those during mid and term pregnancy, and that levels of ATP1B1 mRNA were highest on day (D) 12 of the estrous cycle. In situ hybridization analysis revealed that ATP1A1 and ATP1B1 mRNAs were localized to luminal (LE) and glandular epithelia (GE) in the endometrium. During mid to term pregnancy, localization of ATP1A1 mRNA was confined to LE, GE, and chorionic membrane (CM) of areolae and ATP1- B1 mRNA was localized to LE, GE and CM with the strongest intensity in LE of areolae. Signal intensity of ATP1B1 mRNA in LE was slightly stronger than that in GE. RT-PCR analysis showed that ATP1A1 and ATP1B1 mRNAs were expressed in conceptuses on D12 and D15 of pregnancy. These results showed that ATP1A1 and ATP1B1 were expressed in the uterine endometrium and conceptuses during the estrous cycle and pregnancy in a pregnancy status- and stage-specific manner. These suggest that Na+/K+-ATPase may play a key role in the establishment and maintenance of pregnancy by regulating intracellular concentrations of various ions including calcium at the maternal-fetal interface in pigs.