Department of Neurobiology, University of Oldenburg, Germany.
J Comp Neurol. 2011 Feb 15;519(3):433-50. doi: 10.1002/cne.22526.
In the mouse retina, connexin45 (Cx45) participates in the gap junction between ON cone bipolar cells and AII amacrine cells, which constitutes an essential element of the primary rod pathway. Although it has been shown that Cx45 is also expressed in OFF bipolar cells, its subcellular localization and functional role in these cells are unknown. Here, we analyzed the localization of Cx45 on OFF bipolar cells in the mouse retina. For this, we used wild-type mice and a transgenic mouse line that expressed, in addition to native Cx45, a fusion protein consisting of Cx45 and the enhanced green fluorescent protein (EGFP). Cx45-EGFP expression generates an EGFP signal at gap junctions containing Cx45. Combining immunohistochemistry with intracellular injections, we found that Cx45 was present on dendrites and axon terminals of all OFF bipolar cell types. Cx45 was not found at intersections of two terminal processes of the same type, suggesting that Cx45 might not form gap junctions between axon terminals of the same OFF bipolar cell type but rather might connect OFF bipolar cells to amacrine or ganglion cells. In OFF bipolar cell dendrites, Cx45 was found predominantly in the proximal outer plexiform layer (OPL), well below the cone pedicles. Cx45 did not colocalize with Cx36, which is found predominantly in the distal OPL. We conclude that Cx45 is expressed on OFF bipolar cell dendrites, presumably forming gap junctions with cells of the same type, and on OFF bipolar cell axon terminals, presumably forming heterologous gap junctions with other retinal neurons.
在小鼠视网膜中，连接蛋白 45（Cx45）参与 ON 锥体双极细胞和 AII 无长突细胞之间的缝隙连接，这构成了初级视杆通路的基本元素。尽管已经表明 Cx45 也在 OFF 双极细胞中表达，但它在这些细胞中的亚细胞定位和功能作用尚不清楚。在这里，我们分析了小鼠视网膜中 OFF 双极细胞上 Cx45 的定位。为此，我们使用了野生型小鼠和一种转基因小鼠系，该小鼠系除了表达天然 Cx45 外，还表达了由 Cx45 和增强型绿色荧光蛋白（EGFP）组成的融合蛋白。Cx45-EGFP 的表达会在含有 Cx45 的缝隙连接处产生 EGFP 信号。通过免疫组织化学结合细胞内注射，我们发现 Cx45 存在于所有 OFF 双极细胞类型的树突和轴突末端。在同一类型的两个末端过程的交点处没有发现 Cx45，这表明 Cx45 可能不会在同一 OFF 双极细胞类型的轴突末端之间形成缝隙连接，而是可能将 OFF 双极细胞连接到无长突细胞或节细胞。在 OFF 双极细胞树突中，Cx45 主要存在于近端外丛状层（OPL）中，远低于锥体足。Cx45 与主要存在于远端 OPL 中的 Cx36 不共定位。我们得出结论，Cx45 表达在 OFF 双极细胞树突上，可能与同一类型的细胞形成缝隙连接，并且表达在 OFF 双极细胞轴突末端上，可能与其他视网膜神经元形成异源缝隙连接。
