Abstract
Amoebic Gill Disease (AGD), caused by the protozoan extracellular parasite Paramoeba perurans (P. perurans) is a disease affecting Atlantic salmon (Salmo salar). This study investigated the gill transcriptomic profile of pre-clinical AGD using RNA-sequencing (RNA-seq) technology. RNA-seq libraries generated at 0, 4, 7, 14 and 16 days post infection (dpi) identified 19,251 differentially expressed genes (DEGs) of which 56.2% were up-regulated. DEGs mapped to 224 Gene Ontology (GO) terms including 140 biological processes (BP), 45 cellular components (CC), and 39 molecular functions (MF). A total of 27 reference pathways in the Kyoto Encyclopedia of Genes and Genomes (KEGG) and 15 Reactome gene sets were identified. The RNA-seq data was validated using real-time, quantitative PCR (qPCR). A host immune response though the activation of complement and the acute phase genes was evident at 7 dpi, with a concurrent immune suppression involving cytokine signalling, notably in interleukins, interferon regulatory factors and tumour necrosis factor-alpha (tnf-α) genes. Down-regulated gene expression with involvement in receptor signalling pathways (NOD-like, Toll-like and RIG-1) were also identified. The results of this study support the theory that P. perurans can evade immune surveillance during the initial stages of gill colonisation through interference of signal transduction pathways.
Highlights
Amoebic Gill Disease (AGD), caused by the protozoan extracellular parasite Paramoeba perurans (P. perurans) is a disease affecting Atlantic salmon (Salmo salar)
First described in Tasmania in 19851, AGD is present in most Atlantic salmon producing countries[2] and affects fish during the marine grow out cycle of production at sea temperatures ranging from 7 to 20 °C2
Clinical symptoms of AGD were determined by macroscopic examination of the intact gills in euthanised fish and were scored according to Taylor et al.[6]
Summary
Amoebic Gill Disease (AGD), caused by the protozoan extracellular parasite Paramoeba perurans (P. perurans) is a disease affecting Atlantic salmon (Salmo salar). Resistance to AGD has a moderate heritable genetic component and a recent study combining genome wide association analysis with RNA-seq gene expression profiling in the gill, reported the down-regulation of immune system components during the initial stages of the infection, while genes involved in cell adhesion processes were found to be up-regulated[18]. A dual RNA-seq study investigating the host-parasite interaction identified two transcription factors, znfOZF-like and znf70-like, with involvement in the immune response, cellular proliferation and invasion to be differentially expressed in response to AGD. The aim of this study was to utilise RNA-seq technology to investigate further the gill transcriptome, subsequent to P. perurans colonisation but in advance of mucoid lesion development, in AGD-affected fish, in order to identify biomarkers of early-stage disease
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