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表膜下微管和内膜骨架的共依赖性形成。

Co-dependent formation of the subpellicular microtubules and inner membrane skeleton.

作者信息

Engelberg Klemens, Bauwens Ciara, Ferguson David J P, Gubbels Marc-Jan

机构信息

Department of Biology, Boston College, Chestnut Hill, Massachusetts, USA.

Department of Biological and Medical Sciences, Oxford Brookes University, and NDCLS, Oxford University, Oxford, United Kingdom.

出版信息

mBio. 2025 Aug 13:e0138925. doi: 10.1128/mbio.01389-25.

Abstract

One of the defining features of apicomplexan parasites is their cytoskeleton composed of alveolar vesicles, known as the inner membrane complex (IMC) undergirded by an intermediate filament-like protein network and an array of subpellicular microtubules (SPMTs). In , this specialized cytoskeleton is involved in all aspects of the disease-causing lytic cycle and notably acts as a scaffold for parasite offspring in the internal budding process. Despite advances in our understanding of the architecture and molecular composition, insights pertaining to the coordinated assembly of the scaffold are still largely elusive. Here, tachyzoites were dissected by advanced, iterative expansion microscopy (pan-expansion microscopy), revealing new insights into the very early sequential formation steps of the tubulin and IMC scaffold. A comparative study of the related parasite revealed that different MT bundling organizations of the nascent SPMTs correlate with the number of central and basal alveolar vesicles. In the absence of a so-far identified MT nucleation mechanism, we genetically dissected γ-tubulin and γ-tubulin complex proteins 4, 5, and 6 (GCP4/5/6). While γ-tubulin depletion abolished the formation of the tubulin scaffold, a set of MTs still formed that suggests SPMTs are nucleated at the outer core of the centrosome. Depletion of GCP4/5/6 interfered with the correct assembly of nascent SPMTs into the forming daughter buds, further indicating that the parasite utilizes the γ-tubulin ring complex in tubulin scaffold formation.IMPORTANCEApicomplexan protozoan parasites rely on their specialized cytoskeleton to form offspring. The cytoskeleton serves as an essential scaffold for the emerging daughter cells and is formed by the inner membrane complex (IMC) and underlying subpellicular microtubules (SPMTs). In , the IMC is composed of several membranous sacks and supported by 22 SPMTs, the latter are evenly spaced around the apical end of mature parasites. Although many advances have been made, little is known about the earliest steps of scaffold formation. Here, we gain unprecedented insights into IMC and SPMT establishment via iterative expansion microscopy and comparative cell biology. We show that at the onset of division, SPMTs are grouped and reveal that the number of groups determines the number of IMC sacks that are assembled. We further dissect the parasite's γ-tubulin ring complex and show that it is critically involved in scaffold formation.

摘要

顶复门寄生虫的一个显著特征是其由泡状小泡组成的细胞骨架,即内膜复合体(IMC),其下方是中间丝样蛋白网络和一系列表膜下微管(SPMT)。在 中,这种特殊的细胞骨架参与致病裂解周期的各个方面,尤其在内部出芽过程中作为寄生虫后代的支架。尽管我们对其结构和分子组成的理解取得了进展,但有关支架协同组装的见解仍大多难以捉摸。在这里,通过先进的迭代扩展显微镜(全景扩展显微镜)对速殖子进行剖析,揭示了微管蛋白和IMC支架非常早期的连续形成步骤的新见解。对相关寄生虫的比较研究表明,新生SPMT的不同微管束组织与中央和基底泡状小泡的数量相关。在缺乏迄今已确定的微管成核机制的情况下,我们对γ-微管蛋白和γ-微管蛋白复合体蛋白4、5和6(GCP4/5/6)进行了基因分析。虽然γ-微管蛋白的缺失消除了微管蛋白支架的形成,但仍形成了一组微管,这表明SPMT在中心体的外核心成核。GCP4/5/6的缺失干扰了新生SPMT正确组装到形成的子芽中,进一步表明寄生虫在微管蛋白支架形成中利用了γ-微管蛋白环复合体。重要性顶复门原生动物寄生虫依靠其特殊的细胞骨架来形成后代。细胞骨架作为新出现的子细胞的重要支架,由内膜复合体(IMC)和下面的表膜下微管(SPMT)组成。在 中,IMC由几个膜袋组成,并由22根SPMT支撑,后者在成熟寄生虫顶端均匀分布。尽管已经取得了许多进展,但对支架形成的最早步骤知之甚少。在这里,我们通过迭代扩展显微镜和比较细胞生物学对IMC和SPMT的建立获得了前所未有的见解。我们表明,在分裂开始时,SPMT会聚集在一起,并揭示聚集的数量决定了组装的IMC膜袋的数量。我们进一步剖析了寄生虫的γ-微管蛋白环复合体,并表明它在支架形成中起关键作用。

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