Abstract
Intracellular parasitism in appendicularians has been identified for the first time. Using transmission electron microscopy, cells of microsporidia-like protists have been found in the digestive epithelium of the appendicularian Oikopleura gracilis that externally do not exhibit signs of infection: two morphotypes of cells, interpreted as pre-spore stages, and spores. Cells of the first morphotype are ultrastructurally similar to microsporidial sporonts, with vesicles of the Golgi apparatus visible in their cytoplasm. In cells of the second morphotype, presumably sporoblasts, the envelope is noticeably thicker and specific organelles can be seen in the cytoplasm: three coils of the polar filament and the vacuole. The detected spores (0.7 × 0.9 μm), in a similar manner to microsporidial spores, are covered with a two-layered envelope over the cytoplasmic membrane and contain a polar filament and a polaroplast. In the digestive epithelium of appendicularians, protists cause hypertrophy of invaded enterocytes, deformation of their nuclei, and an increase in the size of mitochondria.
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ACKNOWLEDGMENTS
The author is grateful to Dr. Yu.Ya. Sokolova (Institute of Cytology, Russian Academy of Sciences) and Dr. T.G. Simdyanov (Department of Biology, Moscow State University) for discussing the obtained data, to Dr. S.Sh. Dautov (National Scientific Center of Marine Biology, Far East Branch, Russian Academy of Sciences) for his assistance in collecting the material, and to Dr. I.A. Adameiko (Karolinska Institute, Stockholm, Sweden) for the assistance in photographing live appendicularians. Special thanks are due to D.V. Fomin and K.A. Shefer, the staff of the Far Eastern Center of Electron Microscopy, Center for Collective Use, for their help in operation of the electron microscopes.
Funding
This study was financially supported by the Russian Foundation for Basic Research, project no. 18-34-00357.
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Conflict of interests. The author declares that she has no conflict of interest. Statement on the welfare of animals. All applicable international, national, and/or institutional guidelines for the care and use of animals were followed.
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Translated by E. Shvetsov
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Savelieva, A.V. The First Ultrastructural Description of Appendicularians (Chordata: Tunicata) Infected by Microsporidia-Like Protists. Russ J Mar Biol 45, 145–151 (2019). https://doi.org/10.1134/S1063074019020111
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DOI: https://doi.org/10.1134/S1063074019020111