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Discovery of genes associated with whirling disease infection and resistance in rainbow trout using expression profiling

ABSTRACT: Whirling disease, caused by the pathogen Myxobolus cerebralis, afflicts several salmonid species. Rainbow trout are particularly susceptible and suffer high mortality rates. The disease is persistent and spreading in hatcheries and natural waters of several countries, including the U.S., and the economic losses associated with whirling disease have been extremely large. In this study, gene expression profiling was conducted for resistant and susceptible rainbow trout strains following pathogen exposure with the primary objective of identifying specific genes associated with whirling disease resistance. Several genes were significantly up-regulated in skin following pathogen exposure for both the resistant Hofer and susceptible Trout Lodge rainbow trout strains. For both strains, response to infection appears to be associated with the interferon system. Metallothionein is differentially expressed between the resistant and susceptible strains and is a good candidate for future studies due to its diverse functional roles in inflammation and immune response. The present study has provided the first examination into the genetic basis underlying rainbow trout’s immune response and resistance to the whirling disease pathogen. The identified genes have allowed us to gain initial insight into the molecular mechanisms associated with a salmonid host’s immune response and resistance to whirling disease infection. Keywords: Disease state comparison. 1st comparison: exposed vs control. 2nd comparison: resistant vs susceptible strains

ORGANISM(S): Salmo salar Oncorhynchus mykiss

PROVIDER: GSE8631 | GEO | 2008/02/20

SECONDARY ACCESSION(S): PRJNA101813

REPOSITORIES: GEO

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Project description:Whirling disease, caused by the pathogen Myxobolus cerebralis, afflicts several salmonid species. Rainbow trout are particularly susceptible and suffer high mortality rates. The disease is persistent and spreading in hatcheries and natural waters of several countries, including the U.S., and the economic losses associated with whirling disease have been extremely large. In this study, gene expression profiling was conducted for resistant and susceptible rainbow trout strains following pathogen exposure with the primary objective of identifying specific genes associated with whirling disease resistance. Several genes were significantly up-regulated in skin following pathogen exposure for both the resistant Hofer and susceptible Trout Lodge rainbow trout strains. For both strains, response to infection appears to be associated with the interferon system. Metallothionein is differentially expressed between the resistant and susceptible strains and is a good candidate for future studies due to its diverse functional roles in inflammation and immune response. The present study has provided the first examination into the genetic basis underlying rainbow trout’s immune response and resistance to the whirling disease pathogen. The identified genes have allowed us to gain initial insight into the molecular mechanisms associated with a salmonid host’s immune response and resistance to whirling disease infection. Keywords: Disease state comparison. 1st comparison: exposed vs control. 2nd comparison: resistant vs susceptible strains Resistant (Hofer) and susceptible (Trout Lodge) rainbow trout strains were exposed to 2,000 triactinomyxons (whirling disease pathogen) per fish. Unexposed controls for each strain were treated identically to exposed other than their lack of pathogen exposure. After twenty-four hours, caudal fin tissue was collected for RNA extraction. Amplified RNA was competitively hybridized (exposed versus control) for each strain. Four biological replicates were used for each experimental condition and a balanced block design was incorporated.

Project description:Marker-assisted selective breeding of fish with higher levels of resistance towards specific pathogens has shown successful, but. However, the impact of host genotype on multiple pathogen infections are is still poorly investigated. This study examined the resistance in rainbow trout (Oncorhynchus mykis) towards infection with the eye fluke Diplostomum pseudospathaceum. We used genetically selected rainbow trout, carrying SNPs associated with resistance towards the parasitic ciliate Ichthyophthirius multifiliis, and exposed the fish to eye fluke cercariae. We showed that fish partly resistant to I. multifiliis were more susceptible to eye fluke invasion. Expression The expression of immune relevant genes (encoding innate and adaptive factors) was also affected as these genotypes responded less strongly to a secondary fluke infection. The complexity of genome architecture in disease resistance towards multiple pathogens is discussed. A total of 200 rainbow trout (body weight 14.3-17.7 g, body length 10.2-11.5 cm) were used for the study. Two groups of rainbow trout with high (QTL fish) and low (non-QTL fish) frequency of SNPs associated with I. multifiliis resistance, were hatched from eyed eggs at the disease free recirculated Bornholm Salmon Hatchery, Nexø, Denmark and subsequently reared to the fingerling stage. For this purpose, the first group (QTL-fish) was produced by using sperm from three male genotyped parents carrying SNPs AX-89947214 (Omy17) and AX-89960822 (Omy16), and the other group (non-QTL fish) was produced by using sperm from three other male parents negative for these SNPs. In both cases, sperm was used to fertilize a common pool of eggs stripped from a total of 30 outbred females. Processes of hatching and subsequent rearing of fry to the fingerling stage did not differ between groups of QTL fish and non-QTL fish. From each group (QTL and non-QTL fish) we randomly gathered 100 rainbow trout and transported them (3 h duration) from the hatchery to the infection facility at the University of Copenhagen. Fish were then accommodated and acclimatized 14 d in identical aerated glass tanks with internal biofilters (25 fish per 60 L water, total tank volume 80 L), which were placed in a temperature temperature-controlled room (water temperature constant at 12°C, pH 7.6). We used 30% water change per day to maintain ammonia levels below 0.25. Fish were fed by pelleted feed (1% of fish biomass per day). All fish were genotyped with respect to the two relevant QTLs, one on chomosome 16 and one on chromosome 17. Fish being double heterozugous were excluded from qPCR analysis.

Project description:Through 8 generations of selection, our group has developed a strain of rainbow trout that exhibits high growth rates on an economically and environmentally sustainable all plant protein, high-soy diet. The selected strain also shows superior performance in bacterial and viral disease challenges compared to commercial trout strains, and even a strain specifically selected over many generations for viral and bacterial disease resistance. The selection criteria was strictly focused on performance on plant-based diets, and therefore the physiological mechanisms responsible for the strain’s superior disease resistance remain unresolved. To better characterize the physiological mechanism behind the superior performance of the selected strain we compared the intestinal gene expression of the select strain to that of a commercial control line of trout during an experimental bacterial infection with Flavobacterium psychrophilum (Fp) (CSF 259-93), the causative agent of bacterial cold water disease (BCWD) in salmonids. At 65 days post hatch, all female rainbow trout from the select and commercial strain were stocked separately into four 150L tanks each, at a density of 45 fish per tank. For both strains of trout, three tanks of fish were experimentally infected with Fp by intramuscular injection and one control tank was mock challenged by sham injection. Sampling was conducted at 5 days post challenge (dpc) (Early Infection) and 21 dpc (Late/Recovered Infection). Two intestinal samples from each tank were pooled and two pools from each tank were utilized for RNAseq library preparation. The select strain of trout showed significantly better survival rates (Log-Rank Test, p < 0.0001) over the 21 day infection period, with 70 and 95 % mortality among the select and commercial strain, respectively. Reads from the RNAseq samples were quantified at the transcript level prior to evaluating differential transcript usage and differential gene expression between the strains of trout, infection time points, and disease status.

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Discovery of genes associated with whirling disease infection and resistance in rainbow trout using expression profiling

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