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Ultrastructural and transcriptomic aspects of the Atlantic bluefin tuna Thunnus thynnus (Linnaeus, 1758) gill epithelium infected with Didymosulcus katsuwonicola (Pozdnyakov, 1990).

Didymosulcus katsuwonocila (syn. Didymocystis wedli) is the most abundant didymozoid species infecting farmed Atlantic bluefin tuna (Thunnus thynnus, Scombridae). In most cases infections terminate without any gross pathology, characterised by a significant decrease of cysts per host after couple of months of tuna rearing, however under certain conditions inflammatory and necrotic changes in the gill tissue may be induced, making it an interesting case of hostparasite interaction. The main goal of our study was to analize ultrustructural changes of tuna gill tissue parasitised with D. katsuwonicola and infer functional interpretation at the transcriptomic level. Infected and uninfected gill samples were collected from T. thynnus at harvest after having been farmed for two years and prepared for transmission electron microscopy and transcriptomic profiling by DNA microarrays according to standardized protocols. Micrographs showed numerous transiting vesicles in didymozoid’s tegument in direct contact with host’s loose collagen connective tissue capsule comprising fibrocytes, fibroblasts, eosinophilic-granulated mast cells, eosinophils and plasma cells. The capsule encompassed a nerve composed of three neuronal axons, numerous anastomosing capillaries and was overlaid with multilayered squamous epithelium abundant with mucous goblet cells. The transcriptional profiling revealed moderate gene regulation in both directions with fold changes ranging from -10.38 to 4.56 (N=768 statistically selected features). Pathway analyses based on KEGG sets showed the pertubrations of components of innate immunity, complement and coagulation cascades, as well as endocrine, digestive and nervous functional pathways. The findings elucidate vivid cellular and molecular cross- talk between the host and the parasite.

Thunnus thynnus ; Transcriptome ; Didymosulcus katsuwonicola, microarray, TEM

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