Institute of Biochemistry and Biology, Department of Animal Physiology, University of Potsdam, Karl-Liebknecht-Strasse 24-25, 14476, Potsdam, Germany.
Cell Tissue Res. 2010 May;340(2):215-28. doi: 10.1007/s00441-010-0948-x. Epub 2010 Mar 25.
The Drosophila genome contains at least three loci for the Na,K-ATPase beta-subunit; however, only the protein products of nrv1 and nrv2 have been characterized hitherto. Here, we provide evidence that nrv3 also encodes for a functional Na,K-ATPase beta-subunit, as its protein product co-precipitates with the Na,K-ATPase alpha-subunit. Nrv3 expression in adult flies is restricted to the nervous system in which Nrv3 is enriched in selective types of sensory cells. Because Nrv3 expression is especially prominent in the compound eye, we have analyzed the subcellular and developmental distribution of Nrv3 within the visual cells and related this distribution to those of the alpha-subunit and of the beta-subunits Nrv1 and Nrv2. Prospective visual cells express Nrv2 in the third larval instar stage and during the first half of pupal development. During the last third of pupal life, Nrv3 gradually replaces Nrv2 as the Na,K-ATPase beta-subunit in the photoreceptor cells. Adult photoreceptors express Nrv3 as their major beta-subunit; the visual cells R1-R6 co-express Nrv2 at a low level, whereas R7 and R8 co-express Nrv1. Notably, beta-subunits do not co-distribute exactly with the alpha-subunit at some developmental stages, supporting the concept that the alpha-subunit and beta-subunit can exist in the plasma membrane without being engaged in alpha/beta heterodimers. The non-visual cells within the compound eye express almost exclusively Nrv2, which segregates together with the alpha-subunit to septate junctions throughout development.
果蝇基因组至少包含三个钠钾 ATP 酶β亚基基因位点；然而，迄今为止，只有 nrv1 和 nrv2 的蛋白产物得到了鉴定。在这里，我们提供的证据表明 nrv3 也编码一种功能性的钠钾 ATP 酶β亚基，因为它的蛋白产物与钠钾 ATP 酶α亚基共沉淀。nrv3 在成年果蝇中的表达仅限于神经系统，在神经系统中 nrv3 富集在某些特定类型的感觉细胞中。由于 nrv3 在复眼中的表达尤为显著，我们分析了 nrv3 在视觉细胞中的亚细胞和发育分布，并将其分布与α亚基以及 nrv1 和 nrv2 的β亚基进行了比较。预期的视觉细胞在第三龄幼虫期和蛹发育的前半段表达 nrv2。在蛹发育的最后三分之一阶段，nrv3 逐渐取代 nrv2 成为光感受器细胞中的钠钾 ATP 酶β亚基。成年光感受器细胞主要表达 nrv3 作为其主要β亚基；R1-R6 视细胞低水平共表达 nrv2，而 R7 和 R8 视细胞共表达 nrv1。值得注意的是，β亚基在某些发育阶段与α亚基不完全共分布，这支持了α亚基和β亚基可以在没有形成α/β异二聚体的情况下存在于质膜中的概念。复眼的非视觉细胞几乎只表达 nrv2，该蛋白与α亚基一起在整个发育过程中分离到隔膜连接。
