A novel membrane complex is required for docking and regulated exocytosis of lysosome-related organelles in Tetrahymena thermophila.
A novel membrane complex is required for docking and regulated exocytosis of lysosome-related organelles in Tetrahymena thermophila.
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DOI：
10.1371/journal.pgen.1010194
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发表时间：
2022-05
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影响因子：
4.5
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中科院分区：
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在纤毛虫嗜热四膜虫中，溶酶体相关的细胞器（称为粘液囊）聚集在细胞外周，在那里它们响应细胞外事件分泌其内容物，这种现象称为调节性胞吐。调节胞吐作用的分子基础在动物中已被广泛描述，但目前尚不清楚是否存在类似的机制在纤毛虫或其姐妹谱系，顶复门寄生虫，它们共同属于生态学和医学上重要的超门。以T开头。为了研究嗜热菌突变体在粘液囊胞吐中的作用，我们使用正向遗传方法来揭示MDL1（Mucocyst Discharge with a LamG domain），这是一种对调节粘液囊胞吐作用至关重要的新基因。Mdl1p是一种40 kDa的膜糖蛋白，定位于粘液囊，特别是当粘液囊对接时接触质膜的尖端结构域。Mdl1p的这种亚定位发生在对接之前，强调了粘液囊中的功能不对称性，其与其他肺泡中高度极化的分泌细胞器惊人地相似。LamG结构域中的错义突变导致粘囊停靠但仅经历无效的胞吐作用。相比之下，MDL1的完全敲除在很大程度上阻止了粘液囊自身的对接。Mdl1p与其他9种蛋白质在物理上相关，所有这些蛋白质都是新的，主要限于肺泡，沉降分析支持它们形成一个大复合物的想法。对该假定复合物的其他三个成员（称为MDD（用于粘液囊对接和排出））的分析表明，它们也定位于粘液囊。纯化的MDD复合物的负染色显示具有中央通道的不同颗粒。我们的研究结果揭示了一种新的大分子复合物，其亚基在肺泡细胞中是保守的，但在其他谱系中却不是，这是T.嗜热菌所有的细胞，无论是单细胞原生生物还是多细胞生物，都与它们的环境动态地相互作用。一种重要的相互作用模式是释放分子，这种现象称为分泌，然后可以改变环境以促进有机体的健康。此外，许多细胞具有快速调节分泌途径的能力，使它们能够根据周围环境的变化调整其分泌行为。一个戏剧性的例子是合成并储存分泌分子库的能力，当细胞感觉到特定的环境条件时，这些分子的最终释放被触发。这种现象被称为“受调节的胞吐作用”，并已在动物中进行了长期研究，因为它是不同细胞和组织之间交流的基础。许多单细胞生物也可以通过调节胞吐作用分泌，了解所涉及的机制可能对开发针对几种毁灭性人类寄生虫的疗法产生实际影响。在本文中，我们采取了遗传学的方法来确定参与胞吐在单细胞原生生物，四膜虫的纤毛虫嗜热细胞因子。我们发现，一个新的基因，似乎只存在于四膜虫及其相对密切的进化亲属，在这一途径中发挥着重要作用。我们的研究结果为最近的发现增加了另一层，即像四膜虫这样的细胞进化出了独特的调节胞吐作用的机制，扩大了我们对细胞生物多样性的认识。
In the ciliate Tetrahymena thermophila, lysosome-related organelles called mucocysts accumulate at the cell periphery where they secrete their contents in response to extracellular events, a phenomenon called regulated exocytosis. The molecular bases underlying regulated exocytosis have been extensively described in animals but it is not clear whether similar mechanisms exist in ciliates or their sister lineage, the Apicomplexan parasites, which together belong to the ecologically and medically important superphylum Alveolata. Beginning with a T. thermophila mutant in mucocyst exocytosis, we used a forward genetic approach to uncover MDL1 (Mucocyst Discharge with a LamG domain), a novel gene that is essential for regulated exocytosis of mucocysts. Mdl1p is a 40 kDa membrane glycoprotein that localizes to mucocysts, and specifically to a tip domain that contacts the plasma membrane when the mucocyst is docked. This sub-localization of Mdl1p, which occurs prior to docking, underscores a functional asymmetry in mucocysts that is strikingly similar to that of highly polarized secretory organelles in other Alveolates. A mis-sense mutation in the LamG domain results in mucocysts that dock but only undergo inefficient exocytosis. In contrast, complete knockout of MDL1 largely prevents mucocyst docking itself. Mdl1p is physically associated with 9 other proteins, all of them novel and largely restricted to Alveolates, and sedimentation analysis supports the idea that they form a large complex. Analysis of three other members of this putative complex, called MDD (for Mucocyst Docking and Discharge), shows that they also localize to mucocysts. Negative staining of purified MDD complexes revealed distinct particles with a central channel. Our results uncover a novel macromolecular complex whose subunits are conserved within alveolates but not in other lineages, that is essential for regulated exocytosis in T. thermophila. All cells, whether single-celled protists or multicellular organisms, interact dynamically with their environments. One important mode of interaction is the release of molecules, a phenomenon called secretion, which can then modify the environment to promote the organism’s well-being. Moreover, many cells have the capacity to rapidly adjust the pathways that underlie secretion, allowing them to tailor their secretory behavior in response to changes in their surroundings. A dramatic example of this is the capacity to synthesize and then store reservoirs of secretory molecules, whose eventual release is triggered when the cell senses specific environmental conditions. This phenomenon is called ‘regulated exocytosis’ and has been long studied in animals, because it serves as the basis for communication between different cells and tissues. Many single-celled organisms can also secrete via regulated exocytosis, and understanding the mechanisms involved could have practical consequences for developing therapies against several devastating human parasites. In this paper, we took a genetic approach to identifying factors involved in exocytosis in a single-celled protist, the ciliate Tetrahymena thermophila. We find that a novel gene, which appears to be present only in Tetrahymena and its relatively close evolutionary relatives, plays an important role in the pathway. Our results add another layer to recent findings that cells like Tetrahymena evolved unique mechanisms for regulated exocytosis, expanding our appreciation of cellular biodiversity.
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影响因子：
5.3
作者：
Calow J;Behrens AJ;Mader S;Bockau U;Struwe WB;Harvey DJ;Cormann KU;Nowaczyk MM;Loser K;Schinor D;Hartmann MW;Crispin M
通讯作者：
Crispin M
影响因子：
3.3
作者：
Cowan, AT;Bowman, GR;Turkewitz, AP
通讯作者：
Turkewitz, AP
影响因子：
1.2
作者：
Cingolani, Pablo;Platts, Adrian;Ruden, Douglas M.
通讯作者：
Ruden, Douglas M.
DOI：
10.1016/j.bbamcr.2021.118947
发表时间：
2021-04
期刊：
Biochimica et biophysica acta. Molecular cell research
影响因子：
--
作者：
Docampo R;Huang G
通讯作者：
Huang G
DOI：
10.1083/jcb.69.1.126
发表时间：
1976-04
期刊：
The Journal of cell biology
影响因子：
--
作者：
Beisson J;Lefort-Tran M;Pouphile M;Rossignol M;Satir B
通讯作者：
Satir B