The susceptibility of Atlantic salmon fry to freshwater Infectious Pancreatic Necrosis is largely explained by a major QTL

The Roslin Institute and Royal (Dick) School of Veterinary Studies, University of Edinburgh, Roslin Biocentre, Midlothian, UK.
Heredity (Impact Factor: 3.81). 11/2009; 105(3):318-27. DOI: 10.1038/hdy.2009.171
Source: PubMed


Infectious pancreatic necrosis (IPN) is a viral disease with a significant negative impact on the global aquaculture of Atlantic salmon. IPN outbreaks can occur during specific windows of both the freshwater and seawater stages of the salmon life cycle. Previous research has shown that a proportion of the variation seen in resistance to IPN is because of host genetics, and we have shown that major quantitative trait loci (QTL) affect IPN resistance at the seawater stage of production. In the current study, we completed a large freshwater IPN challenge experiment to allow us to undertake a thorough investigation of the genetic basis of resistance to IPN in salmon fry, with a focus on previously identified QTL regions. The heritability of freshwater IPN resistance was estimated to be 0.26 on the observed scale and 0.55 on the underlying scale. Our results suggest that a single QTL on linkage group 21 explains almost all the genetic variation in IPN mortality under our experimental conditions. A striking contrast in mortality is seen between fry classified as homozygous susceptible versus homozygous resistant, with QTL-resistant fish showing virtually complete resistance to IPN mortality. The findings highlight the importance of the major QTL in the genetic regulation of IPN resistance across distinct physiological lifecycle stages, environmental conditions and viral isolates. These results have clear scientific and practical implications for the control of IPN.

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Available from: B. J. Mcandrew, Mar 14, 2014
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    • "Currently, one key point in understanding immunity against IPNV is to define immunological mechanisms of resistance to infection, which can be assessed by the distinct expression of some immune-related genes. Some groups have focused on the study of the IPN-resistance at the genetic level but these studies have obtained only partial information on the modulation of genes related to immune response (Gheyas et al., 2010; Guy et al., 2009; Houston et al., 2010; Moen et al., 2009; Wetten et al., 2007). The overall immunological response has been only evaluated comparing the responses in Atlantic salmon parr and post-smolt (Lockhart et al., 2007). "
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    ABSTRACT: This study aims to identify at the gene expression level the immune-related genes associated with IPN-susceptible and resistant phenotypes in Atlantic salmon full-sibling families. We have analyzed thirty full-sibling families infected by immersion with IPNV and then classified as resistant or susceptible using a multivariate survival analysis based on a gamma-Cox frailty model and the Kaplan-Meier mortality curves. In four families within each group head kidneys were pooled for real-time PCR and one-color salmon-specific oligonucleotide microarray (21K) analysis at day 1 and 5 post-infection. Transcripts involved in innate response (IL-6, IFN-α), antigen presentation (HSP-70, HSP-90, MHC-I), TH1 response (IL-12, IFN-γ, CRFB6), immunosuppression (IL-10, TGF-β1) and leukocyte activation and migration (CCL-19, CD18) showed a differential expression pattern between both phenotypes, except in IL-6. In susceptible families, except for IFN-γ, the expressions dropped to basal values at day 5 post-infection. In resistant families, unlike susceptible families, levels remained high or increased (except for IL-6) at day 5. Transcriptomic analysis showed that both families have a clear differential expression pattern, resulting in a marked down-regulation in immune related genes involved in innate response, complement system, antigen recognition and activation of immune response in IPN-resistant. Down-regulation of genes, mainly related to tissue differentiation and protein degradation metabolism, was also observed in resistant families. We have identified an immune-related gene patterns associated with susceptibility and resistance to IPNV infection of Atlantic salmon. This suggests that a limited immune response is associated with resistant fish phenotype to IPNV challenge while a highly inflammatory but short response is associated with susceptibility. Copyright © 2015. Published by Elsevier Ltd.
    Full-text · Article · Jun 2015 · Developmental and comparative immunology
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    • "Therefore, challenge tests will often be more accurate and reliable than field outbreaks, due to decreased environmental variability and higher practical feasibility. In fact, challenge testing is currently used to select for resistance to viral, bacterial, and parasitic diseases in breeding programs for Atlantic salmon and rainbow trout (Gjøen and Bentsen, 1997; Leeds et al., 2010; Yáñez and Martínez, 2010; Ødegård et al., 2011; Gjedrem, 2012; Wiens et al., 2013a). "
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    ABSTRACT: Infectious and parasitic diseases generate large economic losses in salmon farming. A feasible and sustainable alternative to prevent disease outbreaks may be represented by genetic improvement for disease resistance. To include disease resistance into the breeding goal, prior knowledge of the levels of genetic variation for these traits is required. Furthermore, the information from the genetic architecture and molecular factors involved in resistance against diseases may be used to accelerate the genetic progress for these traits. In this regard, marker assisted selection and genomic selection are approaches which incorporate molecular information to increase the accuracy when predicting the genetic merit of selection candidates. In this article we review and discuss key aspects related to disease resistance in salmonid species, from both a genetic and genomic perspective, with emphasis in the applicability of disease resistance traits into breeding programs in salmonids.
    Full-text · Article · Nov 2014 · Frontiers in Genetics
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    • "Secondly, comparing the different experiments within which QTL have been (fine) mapped (i.e., Moen et al., 2009; Houston et al., 2010; Gheyas et al., 2010) it may be observed that in some populations the resistance locus is additive; whereas in others it is apparently dominant. Further, this apparent mode of inheritance seems to vary with prevalence of mortality, with lower mortality trials leading to apparent dominance and trials with intermediate mortality leading to additive effects. "
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    ABSTRACT: This paper considers the application of genetic and genomic techniques to disease resistance, the interpretation of data arising from such studies and the utilisation of the research outcomes to breed animals for enhanced resistance. Resistance and tolerance are defined and contrasted, factors affecting the analysis and interpretation of field data presented, and appropriate experimental designs discussed. These general principles are then applied to two detailed case studies, infectious pancreatic necrosis in Atlantic salmon and bovine tuberculosis in dairy cattle, and the lessons learnt are considered in detail. It is concluded that the rate limiting step in disease genetic studies will generally be provision of adequate phenotypic data, and its interpretation, rather than the genomic resources. Lastly, the importance of cross-disciplinary dialogue between the animal health and animal genetics communities is stressed.
    Full-text · Article · Aug 2014 · Livestock Science
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