Abstract

BackgroundTetracapsuloides bryosalmonae is a myxozoan parasite which causes economically important and emerging proliferative kidney disease (PKD) in salmonids. Brown trout, Salmo trutta is a native fish species of Europe, which acts as asymptomatic carriers for T. bryosalmonae. There is only limited information on the molecular mechanism involved in the kidney of brown trout during T. bryosalmonae development. We employed RNA sequencing (RNA-seq) to investigate the global transcriptome changes in the posterior kidney of brown trout during T. bryosalmonae development.MethodsBrown trout were exposed to the spores of T. bryosalmonae and posterior kidneys were collected from both exposed and unexposed control fish. cDNA libraries were prepared from the posterior kidney and sequenced. Bioinformatics analysis was performed using standard pipeline of quality control, reference mapping, differential expression analysis, gene ontology, and pathway analysis. Quantitative real time PCR was performed to validate the transcriptional regulation of differentially expressed genes, and their correlation with RNA-seq data was statistically analyzed.ResultsTranscriptome analysis identified 1169 differentially expressed genes in the posterior kidney of brown trout, out of which 864 genes (74%) were upregulated and 305 genes (26%) were downregulated. The upregulated genes were associated with the regulation of immune system process, vesicle-mediated transport, leucocyte activation, and transport, whereas the downregulated genes were associated with endopeptidase regulatory activity, phosphatidylcholine biosynthetic process, connective tissue development, and collagen catabolic process.ConclusionTo our knowledge, this is the first RNA-seq based transcriptome study performed in the posterior kidney of brown trout during active T. bryosalmonae development. Most of the upregulated genes were associated with the immune system process, whereas the downregulated genes were associated with other metabolic functions. The findings of this study provide insights on the immune responses mounted by the brown trout on the developing parasite, and the host molecular machineries modulated by the parasite for its successful multiplication and release.

Highlights

  • Tetracapsuloides bryosalmonae is a myxozoan parasite which causes economically important and emerging proliferative kidney disease (PKD) in salmonids

  • We identified a strong positive regulation and proliferation of αβ-T cells in the posterior kidney of brown trout during T. bryosalmonae development. αβ-T cells can recognize parasite-derived antigens presented by major histocompatibility complex (MHC) and a noticeable upregulation of MHC class I alpha chain (3075.7-fold) and MHC class II DP beta 2 (2.4-fold) were observed in the posterior kidney of brown trout in our study

  • Our results suggest that T. bryosalmonae proliferation strongly influence apoptotic process in brown trout

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Summary

Introduction

Tetracapsuloides bryosalmonae is a myxozoan parasite which causes economically important and emerging proliferative kidney disease (PKD) in salmonids. Salmo trutta is a native fish species of Europe, which acts as asymptomatic carriers for T. bryosalmonae. Proliferative kidney disease (PKD) is an emerging disease among salmonids caused by the extracellular myxozoan parasite Tetracapsuloides bryosalmonae. PKD is of Sudhagar et al Parasites Vectors (2019) 12:569 trout (Salmo trutta) in the Alpine streams of Europe [5, 6]. Infected bryozoans release parasite spores into the water, which enters the fish via gills. The mature parasitic spores are released by infected fish, mainly brown trout and brook trout, via urine into the aquatic environment, and readily infect bryozoans [9]

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