Abstract Photoreceptors are polarized neurons, with specific subcellular compartmentalization and unique requirements for protein expression and trafficking. Each photoreceptor contains an outer segment (OS) where vision begins, an inner segment (IS) where protein synthesis occurs and a synaptic terminal for signal transmission to second-order neurons. The OS is a large, modified primary cilium attached to the IS by a slender connecting cilium (CC), the equivalent of the transition zone (TZ). Daily renewal of ~10% of the OS requires massive protein biosynthesis in the IS with reliable transport and targeting pathways. Transport of lipidated (‘sticky’) proteins depends on solubilization factors, phosphodiesterase δ (PDEδ) and uncoordinated protein-119 (UNC119), and the cargo dispensation factor (CDF), Arf-like protein 3-guanosine triphosphate (ARL3-GTP). As PDE6 and transducin still reside prominently in the OS of PDEδ and UNC119 germline knockout mice, respectively, we propose the existence of an alternate trafficking pathway, whereby lipidated proteins migrate in rhodopsin-containing vesicles of the secretory pathway.

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扩散或搭便车：光感受器脂化蛋白质如何从这里到那里

摘要 光感受器是极化的神经元，具有特定的亚细胞区室化和蛋白质表达和运输的独特要求。每个光感受器包含一个外段 (OS)，视觉开始处，内段 (IS)，蛋白质合成发生处，以及一个突触终端，用于将信号传输到二级神经元。OS 是通过细长的连接纤毛 (CC) 连接到 IS 的大型改良初级纤毛，相当于过渡区 (TZ)。每天更新约 10% 的 OS 需要在 IS 中进行大量蛋白质生物合成，并具有可靠的运输和靶向途径。脂化（“粘性”）蛋白的运输取决于增溶因子、磷酸二酯酶 δ (PDEδ) 和非协调蛋白 119 (UNC119) 以及货物分配因子 (CDF)，Arf 样蛋白 3-鸟苷三磷酸 (ARL3-GTP)。由于 PDE6 和转导蛋白仍然分别存在于 PDEδ 和 UNC119 种系敲除小鼠的 OS 中，我们提出存在替代运输途径，由此脂质化蛋白质在分泌途径的含视紫质的囊泡中迁移。