PDF(Sci-hub)
Abstract：
Toxoplasma gondii, an obligate intracellular protozoan parasite, infects a wide variety of mammals and birds. Although T. gondii infects the brain and muscles in its latent cyst form containing bradyzoite stage parasites during chronic infection, when a chronically infected host becomes immunodeficient or is preyed upon by a predator, the latent cyst undergoes excystation. However, it is not yet known how T. gondii recognises the triggers of excystation in the microenvironment surrounding the cyst. In this study, we incubated T. gondii cysts from host cells in several solutions containing a variety of ionic compositions. Excystation occurred in a solution with an ionic composition which mimicked that of the extracellular environment. However, excystation did not occur in a solution that mimicked the intracellular environment. We also found that the specific Na+/K+ ratio and the presence of Ca2+, mimicking the extracellular environment, are required to trigger excystation. To examine whether the stage conversion of bradyzoite to tachyzoite occurs prior to egress, we constructed a gene-modified T. gondii strain expressing a green fluorescent protein specifically in the tachyzoite stage. During the process of cyst reactivation of this strain, green fluorescence was detected prior to excystation. This suggests that stage conversion from bradyzoite to tachyzoite occurs prior to cyst disruption. These results indicate that T. gondii bradyzoites monitor the ionic composition of their surroundings to recognise their expulsion from host cells, to effectively time their excystation and stage conversion.
摘要：
弓形虫,一种专性细胞内原生动物寄生虫，感染各种各样的哺乳动物和鸟类。尽管弓形虫在慢性感染期间以含有缓生孢子期寄生虫的潜伏囊肿形式感染大脑和肌肉，当慢性感染的宿主变得免疫缺陷或被捕食者捕食时，潜伏的囊肿经历了囊肿。然而,目前尚不清楚弓形虫如何识别囊肿周围微环境中的细胞外裂的触发因素。在这项研究中,我们将来自宿主细胞的弓形虫囊肿在含有多种离子成分的几种溶液中孵育。异形发生在具有离子成分的溶液中，该离子成分模仿了细胞外环境。然而,在模拟细胞内环境的溶液中没有发生基因外化。我们还发现，特定的Na+/K+比例和Ca2+的存在，模仿细胞外环境，需要触发excystation。为了检查在排出之前是否发生过缓生子到速殖子的阶段转化,我们构建了一个基因修饰的弓形虫菌株，该菌株在速殖子阶段特异性表达绿色荧光蛋白。在该菌株的囊肿重新激活过程中，在切除之前检测到绿色荧光。这表明，在囊肿破裂之前就发生了从缓生子到速殖子的阶段转化。这些结果表明，弓形虫缓子监测其周围环境的离子组成，以识别它们从宿主细胞中的排出，有效地安排它们的灭绝和阶段转换。
