The Function and Structure of the Microsporidia Polar Tube.

Microsporidia are obligate intracellular pathogens that were initially identified about 160 years ago. Current phylogenetic analysis suggests that they are grouped with Cryptomycota as a basal branch or sister group to the fungi. Microsporidia are found worldwide and can infect a wide range of animals from invertebrates to vertebrates, including humans. They are responsible for a variety of diseases once thought to be restricted to immunocompromised patients but also occur in immunocompetent individuals. The small oval spore containing a coiled polar filament, which is part of the extrusion and invasion apparatus that transfers the infective sporoplasm to a new host, is a defining characteristic of all microsporidia. When the spore becomes activated, the polar filament uncoils and undergoes a rapid transition into a hollow tube that will transport the sporoplasm into a new cell. The polar tube has the ability to increase its diameter from approximately 100 nm to over 600 nm to accommodate the passage of an intact sporoplasm and penetrate the plasmalemma of the new host cell. During this process, various polar tube proteins appear to be involved in polar tube attachment to host cell and can interact with host proteins. These various interactions act to promote host cell infection.

微孢子虫是专性细胞内病原体，大约在160年前首次被发现。当前的系统发育分析表明，它们与隐真菌门归为一类，是真菌的一个基部分支或姊妹群。微孢子虫在世界范围内均有发现，能够感染从无脊椎动物到脊椎动物的多种动物，包括人类。它们引发多种疾病，这些疾病曾经被认为仅限于免疫功能低下的患者，但也会发生在免疫功能正常的个体身上。含有卷曲极丝的小椭圆形孢子是所有微孢子虫的一个典型特征，极丝是将感染性孢原质转移到新宿主的挤出和侵入装置的一部分。当孢子被激活时，极丝展开并迅速转变为一个中空的管，这个管将把孢原质运输到一个新细胞中。极管能够将其直径从大约100纳米增加到600纳米以上，以容纳完整的孢原质通过并穿透新宿主细胞的质膜。在这个过程中，各种极管蛋白似乎参与了极管与宿主细胞的附着，并能与宿主蛋白相互作用。这些不同的相互作用促进了宿主细胞的感染。