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.
Bibliographical noteFunding Information:
We thank the Bioinformatics Service Unit at University of Haifa, and the Smoler Proteomics Center at the Technion, for assistance with proteomic analyses. We thank Yulia Pollak (Electron Microscopy Unit at University of Haifa) and the Ishi Talmon group (cryo-SEM, Department of Chemical Engineering, Technion) for their assistance. This research was supported by Research Grant No. IS-4576-13 from BARD, The United States-Israel Binational Agricultural Research and Development Fund and from Grant No. 47496 from USA-Israel Binational Science Foundation (BSF), Jerusalem, Israel.
© 2017 The Author(s).
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