Madsen Steffen S, Bujak Joanna, Tipsmark Christian K
Department of Biology, University of Southern Denmark, DK-5230 Odense M, Denmark Department of Biological Sciences, University of Arkansas, SCEN601, Fayetteville, AR 72701, USA
Department of Biological Sciences, University of Arkansas, SCEN601, Fayetteville, AR 72701, USA.
J Exp Biol. 2014 Sep 1;217(Pt 17):3108-21. doi: 10.1242/jeb.105098. Epub 2014 Jun 19.
We investigated the salinity-dependent expression dynamics of seven aquaporin paralogs (aqp1a, aqp3a, aqp7, aqp8ab, aqp10a, aqp10b and aqp11a) in several tissues of euryhaline Japanese medaka (Oryzias latipes). All paralogs except aqp7 and aqp10a had a broad tissue distribution, and several were affected by salinity in both osmoregulatory and non-osmoregulatory tissues. In the intestine, aqp1a, aqp7, aqp8ab and aqp10a decreased upon seawater (SW) acclimation in both long-term acclimated fish and during 1-3 days of the transition period. In the gill, aqp3a was lower and aqp10a higher in SW than in freshwater (FW). In the kidney no aqps were affected by salinity. In the skin, aqp1a and aqp3a were lower in SW than in FW. In the liver, aqp8ab and aqp10a were lower in SW than in FW. Furthermore, six Na(+),K(+)-ATPase α-subunit isoform transcripts were analysed in the intestine but none showed a consistent response to salinity, suggesting that water transport is not regulated at this level. In contrast, mRNA of the Na(+),K(+),2Cl(-)-cotransporter type-2 strongly increased in the intestine in SW compared with FW fish. Using custom-made antibodies, Aqp1a, Aqp8ab and Aqp10a were localized in the apical region of enterocytes of FW fish. Apical staining intensity strongly decreased, vanished or moved to subapical regions, when fish were acclimated to SW, supporting the lower mRNA expression in SW. Western blots confirmed the decrease in Aqp1a and Aqp10a in SW. The strong decrease in aquaporin expression in the intestine of SW fish is surprising, and challenges the paradigm for transepithelial intestinal water absorption in SW fishes.
我们研究了广盐性日本青鳉（Oryzias latipes）几种组织中七个水通道蛋白旁系同源物（aqp1a、aqp3a、aqp7、aqp8ab、aqp10a、aqp10b和aqp11a）的盐度依赖性表达动态。除aqp7和aqp10a外，所有旁系同源物都有广泛的组织分布，并且有几种在渗透调节组织和非渗透调节组织中均受盐度影响。在肠道中，长期适应海水的鱼以及过渡期的1 - 3天内，aqp1a、aqp7、aqp8ab和aqp10a在海水适应后均减少。在鳃中，海水环境下的aqp3a低于淡水环境，而aqp10a则高于淡水环境。在肾脏中，没有水通道蛋白受盐度影响。在皮肤中，海水环境下的aqp1a和aqp3a低于淡水环境。在肝脏中，海水环境下的aqp8ab和aqp10a低于淡水环境。此外，在肠道中分析了六种Na(+)、K(+)-ATP酶α亚基异构体转录本，但没有一个对盐度表现出一致的反应，这表明水的运输在此水平上不受调节。相反，与淡水鱼相比，海水鱼肠道中Na(+)、K(+)、2Cl(-)-协同转运蛋白2型的mRNA强烈增加。使用定制抗体，Aqp1a、Aqp8ab和Aqp10a定位于淡水鱼肠上皮细胞的顶端区域。当鱼适应海水时，顶端染色强度强烈降低、消失或移至顶端下区域，这支持了海水环境中较低的mRNA表达。蛋白质免疫印迹证实了海水中Aqp1a和Aqp10a的减少。海水鱼肠道中水通道蛋白表达的强烈减少令人惊讶，并挑战了海水鱼经上皮肠道水吸收模式。
