BACKGROUND Changes of the interneuronal coupling mediated by electrical synapse proteins in response to light adaptation and receptive field shaping are a paramount feature in the photoreceptor/horizontal cell/bipolar cell (PRC/HC/BPC) complex of the outer retina. The regulation of these processes is not fully understood at the molecular level but they may require information transfer to the nucleus by locally generated messengers. Electrical synapse proteins may comprise a feasible molecular determinant in such an information-laden signalling pathway. RESULTS Connexin55.5 (Cx55.5) is a connexin with horizontal cell-restricted expression in zebrafish accumulating at dendritic sites within the PRC/HC/BPC complex in form of hemichannels where light-dependent plasticity occurs. Here we provide evidence for the generation of a carboxy-terminal domain of Cx55.5. The protein product is translated from the Cx55.5 mRNA by internal translation initiation from an in-frame ATG codon involving a putative internal ribosome entry site (IRES) element localized in the coding region of Cx55.5. This protein product resembling an 11 kDa domain of Cx55.5 is partially located in the nucleus in vivo and in vitro. CONCLUSION Our results demonstrate the generation of a second protein from the coding region of Cx55.5 by an IRES mediated process. The nuclear occurrence of a fraction of this protein provides first evidence that this electrical synapse protein may participate in a putative cytoplasmic to nuclear signal transfer. This suggests that Cx55.5 could be involved in gene regulation making structural plasticity at the PRC/HC/BPC complex feasible.

中文翻译：

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IRES 介导的水平细胞特异性连接蛋白 Cx55.5 的羧基末端结构域在体内和体外的翻译。

背景由电突触蛋白介导的神经元间耦合的变化响应光适应和感受野成形是外部视网膜的光感受器/水平细胞/双极细胞（PRC/HC/BPC）复合体中的最重要特征。这些过程的调节在分子水平上尚未完全了解，但它们可能需要通过本地生成的信使将信息传输到细胞核。电突触蛋白可能包含这种充满信息的信号通路中可行的分子决定因素。结果 Connexin55.5 (Cx55.5) 是一种在斑马鱼中具有水平细胞限制性表达的连接蛋白，它以半通道的形式在PRC/HC/BPC 复合物内的树突位点积累，其中发生光依赖性可塑性。在这里，我们为生成 Cx55.5 的羧基末端域提供了证据。蛋白质产物是从 Cx55.5 mRNA 通过内部翻译起始从框内 ATG 密码子翻译而来的，该密码子涉及位于 Cx55.5 编码区的推定内部核糖体进入位点 (IRES) 元件。这种类似于 Cx55.5 的 11 kDa 域的蛋白质产品部分位于体内和体外的细胞核中。结论 我们的结果证明了通过 IRES 介导的过程从 Cx55.5 的编码区产生了第二种蛋白质。这种蛋白质的一部分在核中的出现提供了这种电突触蛋白可能参与假定的细胞质到核信号转移的第一个证据。这表明 Cx55.