Response of the Salmon Heart Transcriptome to Pancreas Disease: Differences Between High- and Low-Ranking Families for Resistance

Abstract

pancreas disease caused by salmonid alphaviruses leads to severe losses in Atlantic salmon aquaculture. The aim of our study was to gain a better understanding of the biological differences between salmon with high and low genomic breeding values (H-gEBV and L-gEBV respectively) for pancreas disease resistance. Fish from Hand L-gEBV families were challenged by intraperitoneal injection of salmonid alphavirus or co-habitation with infected fish. Mortality was higher with co-habitation than injection, and for L-than H-gEBV. Heart for RNA-seq and histopathology was collected before challenge and at four-and ten-weeks post-challenge. Heart damage was less severe in injection-challenged H-than L-gEBV fish at week 4. Viral load was lower in H-than L-gEBV salmon after co-habitant challenge. Gene expression differences between Hand L-gEBV manifested before challenge, peaked at week 4, and moderated by week 10. At week 4, H-gEBV salmon showed lower expression of innate antiviral defence genes, stimulation of Band T-cell immune function, and weaker stress responses. Retarded resolution of the disease explains the higher expression of immune genes in L-gEBV at week 10. Results suggest earlier mobilization of acquired immunity better protects H-gEBV salmon by accelerating clearance of the virus and resolution of the disease.

Quantitative trait loci and genes associated with salmonid alphavirus load in Atlantic salmon: implications for pancreas disease resistance and tolerance

“…Despite C t having a lower heritability than P DA , the two traits were found to be highly correlated, and the same QTL region at the proximal end of Ssa03 was found to be associated with both traits. Together with our previous reported finding of lower viral load in H-gEBV fish 33 , this confirms expectations that survival is at least partly dependent on the ability to resist and clear the virus. Tests of viral load therefore have potential application for assessing the relative resistance of fish www.nature.com/scientificreports/ even in the absence of significant mortality caused by pancreas disease.…”

“…Recovery from Heart and Skeletal Muscle Inflammation (HSMI) and PD occurs shortly after marked increase of ig transcripts in the infected sites 43 . The association of the immunoglobulin locus with the viral load QTL is supported by our findings of higher expression of ig light chain in H-gEBV than L-gEBV fish and our finding of higher activity of several genes associated with the recruitment of B-cells nuclear gtpase slip-gc 52 , cd22 36 , in H-gEBV fish at 4 weeks post-SAV infection 33 . The genomic regions encoding IGH were identified as duplicated loci by Yakuike et al 53 and IGH maps to this region of Ssa03 and to an area of Ssa06 in the Atlantic salmon genome 54 56 .…”

“…challenge test trials. The distribution of mortalities across high and low breeding value (EBV) families was described in detail in Robinson et al 33 . Twelve percent mortality was observed over the duration of both trials with higher mortality in the fish with low genomic estimated breeding value (L-gEBV) than high genomic breeding value (H-gEBV) as expected (16.9 and 4.3% mortality in the L-and H-gEBV IP challenge and 20.2 and 7.1% mortality in the L-and H-gEBV CH challenge groups respectively).…”

“…Viral load and histopathological damage to heart tissue after infection with SAV3 is lower in fish with highthan fish with low-genomic breeding values for PD resistance 33 . Lower early viral replication has been found to be associated with resistance to viral disease in salmonid species e.g.…”

“…Knowledge of the biology of resistance to PD have been revealed by comparing the transcriptome of fish with high-and low-genomic breeding values for PD survival at time points before and after challenge with SAV3 33 . Naïve salmon with high genomic breeding values for resistance show a higher expression of genes involved in early antiviral responses compared to naïve salmon with relatively low genomic breeding values for PD resistance.…”