To efficiently enter host cells, apicomplexan parasites such as Toxoplasma gondii rely on an apical complex composed of tubulin-based structures as well as two sets of secretory organelles named micronemes and rhoptries. The trafficking and docking of these organelles to the apical pole of the parasite is crucial for the discharge of their contents. Here, we describe two proteins typically associated with microtubules, Centrin 2 (CEN2) and Dynein Light Chain 8a (DLC8a), that are required for efficient host cell invasion. CEN2 localizes to four different compartments, and remarkably, conditional depletion of the protein occurs in stepwise manner, sequentially depleting the protein pools from each location. This phenomenon allowed us to discern the essential function of the apical pool of CEN2 for microneme secretion, motility, invasion and egress. DLC8a localizes to the conoid, and its depletion also perturbs microneme exocytosis in addition to the apical docking of the rhoptry organelles, causing a severe defect in host cell invasion. Phenotypic characterization of CEN2 and DLC8a indicates that while both proteins participate in microneme secretion, they likely act at different steps along the cascade of events leading to organelle exocytosis.

中文翻译：

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Centrin 2和Dynein轻链8a在弓形虫根尖分泌细胞器排放中的作用。

为了有效地进入宿主细胞，像弓形虫这样的复合体寄生虫需要依靠由微管蛋白为基础的结构以及两套分泌性细胞器（称为微nemes和rhoptry）组成的根尖复合物。这些细胞器的运输和对接至寄生虫的顶极对于释放其内含物至关重要。在这里，我们描述了通常与微管相关的两种蛋白质，即Centrin 2（CEN2）和Dynein轻链8a（DLC8a），它们是有效宿主细胞入侵所必需的。CEN2定位于四个不同的区室，并且值得注意的是，蛋白质的条件耗损以逐步的方式发生，依次从每个位置耗竭蛋白质池。这种现象使我们能够辨别CEN2的根尖池对于微neme分泌，运动，侵袭和流出的基本功能。DLC8a定位在圆锥体上，除根状细胞器的顶端对接外，它的消耗还干扰了微neme胞吐作用，从而导致宿主细胞侵袭的严重缺陷。CEN2和DLC8a的表型特征表明，尽管这两种蛋白都参与微neme的分泌，但它们可能沿导致细胞器胞吐的一系列事件作用于不同的步骤。