Marine Biology Department, The Leon H. Charney School of Marine Sciences University of Haifa, Haifa, 31905, Israel.
Department of Microbiology, Oregon State University, Nash Hall 226, Corvallis, Oregon, 97331, USA.
Sci Rep. 2017 Aug 21;7(1):9010. doi: 10.1038/s41598-017-09955-y.
Myxozoa is a diverse, speciose group of microscopic parasites, recently placed within the phylum Cnidaria. Myxozoans are highly reduced in size and complexity relative to free-living cnidarians, yet they have retained specialized organelles known as polar capsules, akin to the nematocyst stinging capsules of free-living species. Whereas in free-living cnidarians the stinging capsules are used for prey capture or defense, in myxozoans they have the essential function of initiating the host infection process. To explore the evolutionary adaptation of polar capsules to parasitism, we used as a model organism Ceratonova shasta, which causes lethal disease in salmonids. Here, we report the first isolation of C. shasta myxospore polar capsules using a tailored dielectrophoresis-based microfluidic chip. Using electron microscopy and functional analysis we demonstrated that C. shasta tubules have no openings and are likely used to anchor the spore to the host. Proteomic analysis of C. shasta polar capsules suggested that they have retained typical structural and housekeeping proteins found in nematocysts of jellyfish, sea anemones and Hydra, but have lost the most important functional group in nematocysts, namely toxins. Our findings support the hypothesis that polar capsules and nematocysts are homologous organelles, which have adapted to their distinct functions.
粘孢子虫是一类多样化、种类繁多的微小寄生虫，最近被归入刺胞动物门。粘孢子虫在大小和复杂性上相对于自由生活的刺胞动物高度简化，但它们保留了专门的细胞器，称为极囊，类似于自由生活物种的刺丝囊蜇刺胶囊。在自由生活的刺胞动物中，刺丝囊用于捕捉猎物或防御，而在粘孢子虫中，它们具有启动宿主感染过程的重要功能。为了探索极囊对寄生的进化适应，我们以引起鲑鱼致命疾病的 Ceratonova shasta 为模型生物。在这里，我们报告了使用定制的基于电介质电泳的微流控芯片首次分离出 C. shasta 粘孢子极囊。通过电子显微镜和功能分析，我们证明 C. shasta 小管没有开口，可能用于将孢子固定在宿主上。C. shasta 极囊的蛋白质组学分析表明，它们保留了在水母、海葵和水螅的刺丝囊中发现的典型结构和管家蛋白，但失去了刺丝囊最重要的功能群，即毒素。我们的发现支持这样的假设，即极囊和刺丝囊是同源的细胞器，它们已经适应了它们的不同功能。
