Microtubule stability and dynamics in Plasmodium sporozoites

微管是由α-微管蛋白和β-微管蛋白的二聚体形成的长丝状结构。微管动态地形成和分解，这些动态对于许多细胞过程是必不可少的。翻译后修饰和微管结合蛋白在调节微管动力学中起关键作用。引起疟疾的疟原虫寄生虫属于染色泡纲中的顶复纲，是一种不同的生命形式，其细胞生物学与酵母等后角体模式生物不同。与其他生物一样，疟原虫中的微管对细胞分裂、囊泡运输、运动和寄生虫形态发生都很重要。一些微管动力学的抑制剂已被证明可以杀死生长期的寄生虫，但一旦形成，微管就非常稳定。我们最近发现，删除两个α-微管蛋白基因之一，可以阻止疟原虫子孢子的形成，这种子孢子是由按蚊传播的。在这些α1-微管蛋白（-）寄生虫中，在形成子孢子的寄生卵囊内没有微管形成。值得注意的是，当用α 2-微管蛋白基因补充这种缺失时，形成的子孢子显示出更少更短的微管，并且具有异常的形状。引人注目的是，子孢子较短，并显示出较强的曲率，这导致这些高度运动的寄生虫的不同运动路径。这些α 2-微管蛋白补充寄生虫的感染性低于野生型或α 1-微管蛋白补充对照系，但可以完成寄生虫的生命周期。在子孢子形成期间对微管长度的详细显微分析揭示了在子孢子形成期间微管令人惊讶地生长至超过12微米，随后在寄生虫形成完成后，野生型的微管收缩至约6微米，突变体的微管收缩至4.5微米。我们现在想解决两种α-微管蛋白同种型不同行为的确切分子基础，并产生具有较长微管的寄生虫，以测试这些如何影响子孢子形状和感染性。为此，我们将产生一系列表达嵌合α-微管蛋白基因的寄生虫系。此外，我们还将研究可能影响微管稳定性的乙酰化位点的功能。

Microtubules are long filamentous structures formed from dimers of alpha- and ß-tubulin. Microtubules form and disassemble dynamically and these dynamics are essential for many cellular processes. Post-translational modifications and microtubule binding proteins play key roles in modulating microtubule dynamics. Malaria causing Plasmodium parasites belong to the apicomplexa within the chromalveolata and are divergent life forms with a cellular biology distinct to opisthokont model organisms such as yeast. Like in other organisms, microtubules in Plasmodia are important for cell division, vesicular transport, motility and parasite morphogenesis. Some inhibitors of microtubule dynamics have been shown to kill parasites in their growth phase but once formed the microtubules are remarkably stable. We recently showed that deletion of one of the two alpha-tubulin genes blocks formation of Plasmodium sporozoites, the forms transmitted by the Anopheles mosquito. In these α1-tubulin(-) parasites, no microtubules formed inside the parasitic oocysts where sporozoites are formed. Remarkably, when complementing this deletion with the alpha2-tubulin gene sporozoites formed that showed fewer and shorter microtubules and had an aberrant shape. Strikingly, sporozoites were shorter and showed a stronger curvature, which lead to different movement paths of these highly motile parasites. These alpha2-tubulin complemented parasites were less infectious than the wild type or alpha1-tubulin complemented control lines but could complete the parasite life cycle. Detailed microscopic analysis of microtubule length during the formation of the sporozoites revealed a surprising growth of microtubules to over 12 micrometer during sporozoite formation followed by a shrinkage to about 6 micrometer after parasite formation is completed for the wild type and to 4.5 micrometer in the mutant. We now want to address the exact molecular basis for the different behaviors of the two alpha-tubulin isotypes and generate parasites with longer microtubules to test how these impact on sporozoite shape and infectivity. To do so we will generate a series of parasite lines expressing chimeric alpha-tubulin genes. In addition we will investigate the functionality of an acetylation site that could impact microtubule stability.