Abstract
BackgroundWhirling disease, caused by the pathogen Myxobolus cerebralis, afflicts several salmonid species. Rainbow trout are particularly susceptible and may suffer high mortality rates. The disease is persistent and spreading in hatcheries and natural waters of several countries, including the U.S.A., and the economic losses attributed to whirling disease are substantial. In this study, genome-wide expression profiling using cDNA microarrays was conducted for resistant Hofer and susceptible Trout Lodge rainbow trout strains following pathogen exposure with the primary objective of identifying specific genes implicated in whirling disease resistance.ResultsSeveral genes were significantly up-regulated in skin following pathogen exposure for both the resistant and susceptible rainbow trout strains. For both strains, response to infection appears to be linked with the interferon system. Expression profiles for three genes identified with microarrays were confirmed with qRT-PCR. Ubiquitin-like protein 1 was up-regulated over 100 fold and interferon regulating factor 1 was up-regulated over 15 fold following pathogen exposure for both strains. Expression of metallothionein B, which has known roles in inflammation and immune response, was up-regulated over 5 fold in the resistant Hofer strain but was unchanged in the susceptible Trout Lodge strain following pathogen exposure.ConclusionThe present study has provided an initial view into the genetic basis underlying immune response and resistance of rainbow trout to the whirling disease parasite. The identified genes have allowed us to gain insight into the molecular mechanisms implicated in salmonid immune response and resistance to whirling disease infection.
Highlights
Whirling disease, caused by the pathogen Myxobolus cerebralis, afflicts several salmonid species
In order to study genes involved in whirling disease response, resistant and susceptible rainbow trout strains were exposed to M. cerebralis and RNA from skin tissue was converted to cDNA and hybridized onto microarrays
A combined total of 17 genes or features (14 annotated genes, 3 unknown features) were differentially expressed in one or both strains following pathogen exposure and are involved with rainbow trout infection response to whirling disease exposure. Several of these genes were found in different locations on the array as unique expressed sequence tag (EST) clones and their repeated presence on the significance gene lists provides additional support for their involvement in the whirling disease phenotype
Summary
Whirling disease, caused by the pathogen Myxobolus cerebralis, afflicts several salmonid species. Whirling disease was first described among farmed rainbow trout (Oncorhynchus mykiss), a native North American salmonid species, introduced to Germany as a food fish in the late 1800s [1]. Rainbow trout are highly susceptible to whirling disease and the introduction of the parasite to the U.S.A. in the 1950s had immediate economic impacts on salmonid hatcheries in both eastern and western states [2]. Concerns continue over the potential negative ecologic impacts of whirling disease on wild salmonid populations, threatened or endangered salmonids such as bull trout (Salvelinus confluentus), cutthroat trout (Oncorhynchus clarki), and steelhead (Oncorhynchus mykiss) [8,9]
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