Single-celled tubules represent a complicated structure that forms during development, requiring extension of a narrow cytoplasm surrounding a lumen exerting osmotic pressure that can burst the luminal membrane. Genetic studies on the excretory canal cell of Caenorhabditis elegans have revealed many proteins that regulate the cytoskeleton, vesicular transport, and physiology of the narrow canals. Here, we show that βH-spectrin regulates the placement of intermediate filament proteins forming a terminal web around the lumen, and that the terminal web in turn retains a highly conserved protein (EXC-9/CRIP1) that regulates apical endosomal trafficking. EXC-1/IRG, the binding partner of EXC-9, is also localized to the apical membrane and affects apical actin placement and RAB-8–mediated vesicular transport. The results suggest that an intermediate filament protein acts in a novel pathway to direct the traffic of vesicles to locations of lengthening apical surface during single-celled tubule development.

中文翻译：

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末端网和囊泡运输蛋白介导线虫单细胞管发生

单细胞小管代表了在发育过程中形成的复杂结构，需要围绕管腔延伸狭窄的细胞质，施加渗透压，从而使管腔膜破裂。对秀丽隐杆线虫排泄管细胞的遗传学研究揭示了许多调节细胞骨架、囊泡运输和狭窄管生理学的蛋白质。在这里，我们发现βH-血影蛋白调节中间丝蛋白的位置，形成管腔周围的末端网，而末端网又保留了调节顶端内体运输的高度保守的蛋白质（EXC-9/CRIP1）。EXC-1/IRG 是 EXC-9 的结合伴侣，也定位于顶膜并影响顶肌动蛋白的位置和 RAB-8 介导的囊泡运输。结果表明，在单细胞小管发育过程中，中间丝蛋白以一种新的途径发挥作用，将囊泡运输至延长顶端表面的位置。