Dorgau Birthe, Herrling Regina, Schultz Konrad, Greb Helena, Segelken Jasmin, Ströh Sebastian, Bolte Petra, Weiler Reto, Dedek Karin, Janssen-Bienhold Ulrike
Department of Neurobiology, University of Oldenburg, D-26111, Oldenburg, Germany.
Institute of Genetic Medicine, Newcastle University, Newcastle, UK.
J Comp Neurol. 2015 Oct 1;523(14):2062-81. doi: 10.1002/cne.23779. Epub 2015 May 14.
Horizontal cells in the mouse retina are of the axon-bearing B-type and contribute to the gain control of photoreceptors and to the center-surround organization of bipolar cells by providing feedback and feedforward signals to photoreceptors and bipolar cells, respectively. Horizontal cells form two independent networks, coupled by dendro-dendritic and axo-axonal gap junctions composed of connexin57 (Cx57). In Cx57-deficient mice, occasionally the residual tracer coupling of horizontal cell somata was observed. Also, negative feedback from horizontal cells to photoreceptors, potentially mediated by connexin hemichannels, appeared unaffected. These results point to the expression of a second connexin in mouse horizontal cells. We investigated the expression of Cx50, which was recently identified in axonless A-type horizontal cells of the rabbit retina. In the mouse retina, Cx50-immunoreactive puncta were predominantly localized on large axon terminals of horizontal cells. Electron microscopy did not reveal any Cx50-immunolabeling at the membrane of horizontal cell tips invaginating photoreceptor terminals, ruling out the involvement of Cx50 in negative feedback. Moreover, Cx50 colocalized only rarely with Cx57 on horizontal cell processes, indicating that both connexins form homotypic rather than heterotypic or heteromeric gap junctions. To check whether the expression of Cx50 is changed when Cx57 is lacking, we compared the Cx50 expression in wildtype and Cx57-deficient mice. However, Cx50 expression was unaffected in Cx57-deficient mice. In summary, our results indicate that horizontal cell axon terminals form two independent sets of homotypic gap junctions, a feature which might be important for light adaptation in the retina.
小鼠视网膜中的水平细胞属于有轴突的B型细胞，通过分别向光感受器和双极细胞提供反馈和前馈信号，对光感受器的增益控制以及双极细胞的中心 - 外周组织形成有贡献。水平细胞形成两个独立的网络，通过由连接蛋白57（Cx57）组成的树突 - 树突和轴突 - 轴突缝隙连接耦合。在Cx57基因缺陷的小鼠中，偶尔会观察到水平细胞胞体的残余示踪剂耦合。此外，水平细胞对光感受器的负反馈（可能由连接蛋白半通道介导）似乎未受影响。这些结果表明小鼠水平细胞中存在第二种连接蛋白的表达。我们研究了Cx50的表达，Cx50最近在兔视网膜的无轴突A型水平细胞中被鉴定出来。在小鼠视网膜中，Cx50免疫反应性斑点主要定位于水平细胞的大轴突终末。电子显微镜未在水平细胞尖端内陷光感受器终末的膜上发现任何Cx50免疫标记，排除了Cx50参与负反馈的可能性。此外，Cx50在水平细胞突起上仅很少与Cx57共定位，表明这两种连接蛋白形成同型而非异型或异源缝隙连接。为了检查当Cx57缺乏时Cx50的表达是否发生变化，我们比较了野生型和Cx57基因缺陷小鼠中Cx50的表达。然而，Cx50的表达在Cx57基因缺陷小鼠中未受影响。总之，我们的结果表明水平细胞轴突终末形成两组独立的同型缝隙连接，这一特征可能对视网膜的光适应很重要。
