Discovery of genes implicated in whirling disease infection and resistance in rainbow trout using genome-wide expression profiling

<p>Abstract</p> <p>Background</p> <p>Whirling disease, caused by the pathogen <it>Myxobolus cerebralis</it>, 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.</p> <p>Results</p> <p>Several 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. <it>Ubiquitin-like protein 1 </it>was up-regulated over 100 fold and <it>interferon regulating factor 1 </it>was up-regulated over 15 fold following pathogen exposure for both strains. Expression of <it>metallothionein B</it>, 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.</p> <p>Conclusion</p> <p>The 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.</p

Transcriptional Response to Acute Thermal Exposure in Juvenile Chinook Salmon Determined by RNAseq.

Thermal exposure is a serious and growing challenge facing fish species worldwide. Chinook salmon (Oncorhynchus tshawytscha) living in the southern portion of their native range are particularly likely to encounter warmer water due to a confluence of factors. River alterations have increased the likelihood that juveniles will be exposed to warm water temperatures during their freshwater life stage, which can negatively impact survival, growth, and development and pose a threat to dwindling salmon populations. To better understand how acute thermal exposure affects the biology of salmon, we performed a transcriptional analysis of gill tissue from Chinook salmon juveniles reared at 12° and exposed acutely to water temperatures ranging from ideal to potentially lethal (12° to 25°). Reverse-transcribed RNA libraries were sequenced on the Illumina HiSeq2000 platform and a de novo reference transcriptome was created. Differentially expressed transcripts were annotated using Blast2GO and relevant gene clusters were identified. In addition to a high degree of downregulation of a wide range of genes, we found upregulation of genes involved in protein folding/rescue, protein degradation, cell death, oxidative stress, metabolism, inflammation/immunity, transcription/translation, ion transport, cell cycle/growth, cell signaling, cellular trafficking, and structure/cytoskeleton. These results demonstrate the complex multi-modal cellular response to thermal stress in juvenile salmon

Characterization of 24 Microsatellite Loci in Delta Smelt, \u3ci\u3eHypomesus transpacificus\u3c/i\u3e, and Their Cross-Species Amplification in Two Other Smelt Species of the Osmeridae Family

We characterized 24 polymorphic tetranucleotide microsatellite loci for delta smelt (Hypomesus transpacificus) endemic to the San Francisco Bay Estuary, California, USA. Screening of samples (n = 30) yielded two to 26 alleles per locus with observed levels of heterozygosity ranging from 0.17 to 1.0. Only one locus deviated from Hardy–Weinberg equilibrium, suggesting these individuals originate from a single panmictic population. Linkage disequilibrium was found in two pairs of loci after excluding the locus out of Hardy–Weinberg equilibrium. Twenty-two primer pairs cross-amplified in wakasagi smelt (Hypomesus nipponensis), and 15 primer pairs cross-amplified in longfin smelt (Spirinchus thaleichthys)

Survival and reproduction of Myxobolus cerebralis-resistant rainbow trout introduced to the Colorado river and increased resistance of age-0 progeny.

Myxobolus cerebralis caused severe declines in rainbow trout populations across Colorado following its introduction in the 1980s. One promising approach for the recovery of Colorado's rainbow trout populations has been the production of rainbow trout that are genetically resistant to the parasite. We introduced one of these resistant crosses, known as the GR×CRR (cross between the German Rainbow [GR] and Colorado River Rainbow [CRR] trout strains), to the upper Colorado River. The abundance, survival, and growth of the stocked GR×CRR population was examined to determine if GR×CRRs had contributed offspring to the age-0 population, and determine whether these offspring displayed increased resistance and survival characteristics compared to their wild CRR counterparts. Apparent survival of the introduced GR×CRR over the entire study period was estimated to be 0.007 (±0.001). Despite low survival of the GR×CRRs, age-0 progeny of the GR×CRR were encountered in years 2008 through 2011. Genetic assignments revealed a shift in the genetic composition of the rainbow trout fry population over time, with CRR fish comprising the entirety of the fry population in 2007, and GR-cross fish comprising nearly 80% of the fry population in 2011. A decrease in average infection severity (myxospores fish-1) was observed concurrent with the shift in the genetic composition of the rainbow trout fry population, decreasing from an average of 47,708 (±8,950) myxospores fish-1 in 2009 to 2,672 (±4,379) myxospores fish-1 in 2011. Results from this experiment suggest that the GR×CRR can survive and reproduce in rivers with a high prevalence of M. cerebralis. In addition, reduced myxospore burdens in age-0 fish indicated that stocking this cross may ultimately lead to an overall reduction in infection prevalence and severity in the salmonid populations of the upper Colorado River

Isolation and characterization of microsatellite loci in two non-native hydromedusae in the San Francisco Estuary: Maeotias marginata and Moerisia sp.

We characterized 10 new microsatellite markers in each of two species of hydromedusae, Maeotias marginata and Moerisia sp. Genetic diversity was estimated using 20–41 individuals collected from Suisun Marsh within the San Francisco Estuary, CA. Allelic richness ranged from 5–9 in M. marginata and 2–10 in Moerisia sp. with average expected heterozygosities of 0.71 and 0.57 respectively. One locus in M. marginata and two in Moerisia sp. deviated from Hardy–Weinberg equilibrium expectations, likely due to null alleles

Genetic Considerations for Sourcing Steelhead Reintroductions: Investigating Possibilities for the San Joaquin River

Steelhead trout (Oncorhynchus mykiss) historically occurred in all major watersheds along the west coast of the United States. They can be a vital part of a healthy riverine ecosystem, are highly valued for fishing, and have been greatly affected by human activities. Given these traits, and that the San Joaquin River in the Central Valley of California is under consideration for steelhead reintroduction, emphasis has recently been placed on conservation efforts to reintroduce steelhead into streams in which they were once native. There are many issues to consider when deciding how, where, and in what manner to reintroduce steelhead, including genetic considerations. One primary factor is determining the source population for reintroduction. In this paper, we consider the many important genetic aspects to consider when determining the source for steelhead reintroduction, and outline the genetic data needs when determining sources for reintroduction. We discuss the lessons learned from previous reintroductions in relation to a reintroduction scenario in the San Joaquin River, and recommend potential source populations

Identifying hidden biocomplexity and genomic diversity in Chinook salmon, an imperiled species with a history of anthropogenic influence

Biocomplexity is an important mechanism for population resilience in changing environments. However, we are just beginning to understand how to identify biocomplexity so that species management efforts promote resilience and stability. Genomic techniques are emerging as an important method for identifying biocomplexity. Central Valley (CV) Chinook salmon are an example of a species at risk of extinction if better methods for identifying and protecting biocomplexity are not employed. To address this knowledge gap, we employed restriction site associated DNA sequencing to conduct the first genomic study of all major populations of CV Chinook salmon. We found greater population structure across the Central Valley than previously documented. Additionally, we show evidence for differentiation and adaptation within migratory phenotypes despite high levels of gene flow. We also determined that genomic data can vastly improve our ability to assign individuals to their natal populations, even as they mix during migration, a finding that will assist management practices. These results demonstrate how genomic study can greatly improve our ability to identify and conserve biocomplexity.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Genetic Considerations for Sourcing Steelhead Reintroductions: Investigating Possibilities for the San Joaquin River

Steelhead trout (Oncorhynchus mykiss) historically occurred in all major watersheds along the west coast of the United States. They can be a vital part of a healthy riverine ecosystem, are highly valued for fishing, and have been greatly affected by human activities. Given these traits, and that the San Joaquin River in the Central Valley of California is under consideration for steelhead reintroduction, emphasis has recently been placed on conservation efforts to reintroduce steelhead into streams in which they were once native. There are many issues to consider when deciding how, where, and in what manner to reintroduce steelhead, including genetic considerations. One primary factor is determining the source population for reintroduction. In this paper, we consider the many important genetic aspects to consider when determining the source for steelhead reintroduction, and outline the genetic data needs when determining sources for reintroduction. We discuss the lessons learned from previous reintroductions in relation to a reintroduction scenario in the San Joaquin River, and recommend potential source populations