Abstract
BackgroundThe viral hemorrhagic septicemia virus (VHSV) is a major threat for salmonid farming and for wild fish populations worldwide. Previous studies have highlighted the importance of innate factors regulated by a major quantitative trait locus (QTL) for the natural resistance to waterborne VHSV infection in rainbow trout. The aim of this study was to analyze the early transcriptomic response to VHSV inoculation in cell lines derived from previously described resistant and susceptible homozygous isogenic lines of rainbow trout to obtain insights into the molecular mechanisms responsible for the resistance to the viral infection.ResultsWe first confirmed the presence of the major QTL in a backcross involving a highly resistant fish isogenic line (B57) and a highly susceptible one (A22), and were able to define the confidence interval of the QTL and to identify its precise position. We extended the definition of the QTL since it controls not only resistance to waterborne infection but also the kinetics of mortality after intra-peritoneal injection. Deep sequencing of the transcriptome of B57 and A22 derived cell lines exposed to inactivated VHSV showed a stronger response to virus inoculation in the resistant background. In line with our previous observations, an early and strong induction of interferon and interferon-stimulated genes was correlated with the resistance to VHSV, highlighting the major role of innate immune factors in natural trout resistance to the virus. Interestingly, major factors of the antiviral innate immunity were much more expressed in naive B57 cells compared to naive A22 cells, which likely contributes to the ability of B57 to mount a fast antiviral response after viral infection. These observations were further extended by the identification of several innate immune-related genes localized close to the QTL area on the rainbow trout genome.ConclusionsTaken together, our results improve our knowledge in virus-host interactions in vertebrates and provide novel insights in the molecular mechanisms explaining the resistance to VHSV in rainbow trout. Our data also provide a collection of potential markers for resistance and susceptibility of rainbow trout to VHSV infection.
Highlights
The viral hemorrhagic septicemia virus (VHSV) is a major threat for salmonid farming and for wild fish populations worldwide
Using B57 and A22 derived offspring infected with VHSV, we first confirmed through a genetic study that the major quantitative trait locus (QTL), which we previously identified on rainbow trout chromosome 3 (RT31 linkage group) [13], was effectively present in these genetic backgrounds
A major QTL controls the differences of resistance to VHSV in B57 and A22 fish To understand the mechanisms underlying the differences of susceptibility to VHSV between B57 and A22 isogenic lines, we first looked for the presence of the major QTL we previously identified [13]
Summary
The viral hemorrhagic septicemia virus (VHSV) is a major threat for salmonid farming and for wild fish populations worldwide. The correlation between fish survival and virus load in infected fin explants [10, 11] strongly suggests the contribution of innate or intrinsic virus resistance cellular factors Another striking evidence was the exquisite correlation between both the resistance to waterborne VHSV infection of rainbow trout isogenic lines and of the fibroblast-like cell lines derived from these fish [12]. A differential induction of ISG based on genetic background, in kinetics or amplitude, may explain variation in the outcome of a viral infection In this context, a comparison of transcriptome responses at an early stage of VHSV infection between resistant and susceptible fish would help to understand the resistance mechanisms
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