title: Transcriptome analyses of amoebic gill disease-affected Atlantic salmon (Salmo salar) tissues reveal localized host gene suppression.
abstract: The transcriptome response of Atlantic salmon (Salmo salar) displaying advanced stages of amoebic gill disease (AGD) was investigated. Naïve smolt were challenged with AGD for 19 days, at which time all fish were euthanized and their severity of infection quantified through histopathological scoring. Gene expression profiles were compared between heavily infected and naïve individuals using a 17 K Atlantic salmon cDNA microarray with real-time quantitative RT-PCR (qPCR) verification. Expression profiles were examined in the gill, anterior kidney, and liver. Twenty-seven transcripts were significantly differentially expressed within the gill; 20 of these transcripts were down-regulated in the AGD-affected individuals compared with naïve individuals. In contrast, only nine transcripts were significantly differentially expressed within the anterior kidney and five within the liver. Again the majority of these transcripts were down-regulated within the diseased individuals. A down-regulation of transcripts involved in apoptosis (procathepsin L, cathepsin H precursor, and cystatin B) was observed in AGD-affected Atlantic salmon. Four transcripts encoding genes with antioxidant properties also were down-regulated in AGD-affected gill tissue according to qPCR analysis. The most up-regulated transcript within the gill was an unknown expressed sequence tag (EST) whose expression was 218-fold (+/- SE 66) higher within the AGD affected gill tissue. Our results suggest that Atlantic salmon experiencing advanced stages of AGD demonstrate general down-regulation of gene expression, which is most pronounced within the gill. We propose that this general gene suppression is parasite-mediated, thus allowing the parasite to withstand or ameliorate the host response.
authors.affiliation: CSIRO National Food Futures Flagship, CSIRO Marine and Atmospheric Research, Hobart, Tasmania, Australia. james.wynne@csiro.au
authors.forename: James W
authors.initials: JW
authors.lastname: Wynne
authors.forename: Maree G
authors.initials: MG
authors.lastname: O'Sullivan
authors.forename: Mathew T
authors.initials: MT
authors.lastname: Cook
authors.forename: Glenn
authors.initials: G
authors.lastname: Stone
authors.forename: Barbara F
authors.initials: BF
authors.lastname: Nowak
authors.forename: David R
authors.initials: DR
authors.lastname: Lovell
authors.forename: Nicholas G
authors.initials: NG
authors.lastname: Elliott
mesh_terms: D016841:Amoebida / Q000502:physiology*; D000818:Animals; D005393:Fish Diseases / Q000235:genetics* / Q000469:parasitology*; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D005880:Gills / Q000378:metabolism / Q000469:parasitology* / Q000473:pathology; D007668:Kidney / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D011528:Protozoan Infections / Q000235:genetics / Q000469:parasitology; D011529:Protozoan Infections, Animal; D015203:Reproducibility of Results; D020317:Salmo salar / Q000235:genetics* / Q000469:parasitology*