De novo assembly of Sockeye salmon kidney transcriptomes reveal a limited early response to piscine reovirus with or without infectious hematopoietic necrosis virus superinfection.
Piscine reovirus (PRV) has been associated with the serious disease known as Heart and Skeletal Muscle Inflammation (HSMI) in cultured Atlantic salmon Salmo salar in Norway. PRV is also prevalent in wild and farmed salmon without overt disease manifestations, suggesting multifactorial triggers or PRV variant-specific factors are required to initiate disease. In this study, we explore the head kidney transcriptome of Sockeye salmon Oncorhynchus nerka during early PRV infection to identify host responses in the absence of disease in hopes of elucidating mechanisms by which PRV may directly alter host functions and contribute to the development of a disease state. We further investigate the role of PRV as a coinfecting agent following superinfection with infectious hematopoietic necrosis virus (IHNV) - a highly pathogenic rhabdovirus endemic to the west coast of North America.



Challenge of Sockeye salmon with PRV resulted in high quantities of viral transcripts to become present in the blood and kidney of infected fish without manifestations of disease. De novo transcriptome assembly of over 2.3 billion paired RNA-seq reads from the head kidneys of 36 fish identified more than 320,000 putative unigenes, of which less than 20 were suggested to be differentially expressed in response to PRV at either 2 or 3 weeks post challenge by DESeq2 and edgeR analysis. Of these, only one, Ependymin, was confirmed to be differentially expressed by qPCR in an expanded sample set. In contrast, IHNV induced substantial transcriptional changes (differential expression of > 20,000 unigenes) which included transcripts involved in antiviral and inflammatory response pathways. Prior infection with PRV had no significant effect on host responses to superinfecting IHNV, nor did host responses initiated by IHNV exposure influence increasing PRV loads.



PRV does not substantially alter the head kidney transcriptome of Sockeye salmon during early (2 to 3 week) infection and dissemination in a period of significant increasing viral load, nor does the presence of PRV change the host transcriptional response to an IHNV superinfection. Further, concurrent infections of PRV and IHNV do not appear to significantly influence the infectivity or severity of IHNV associated disease, or conversely, PRV load.
Fisheries and Oceans Canada, Pacific Biological Station, 3190 Hammond Bay Rd, Nanaimo, BC, V9T6N7, Canada. Mark.Polinski@dfo-mpo.gc.ca.
Mark P
MP
Polinski
Fisheries and Oceans Canada, Pacific Biological Station, 3190 Hammond Bay Rd, Nanaimo, BC, V9T6N7, Canada.
Julia C
JC
Bradshaw
Department of Ocean Sciences, Memorial University, St. John's, NF, A1C5S7, Canada.
Sabrina M
SM
Inkpen
Fisheries and Oceans Canada, Pacific Biological Station, 3190 Hammond Bay Rd, Nanaimo, BC, V9T6N7, Canada.
Jon
J
Richard
Department of Pathology, Norwegian Veterinary Institute, Oslo, NO-0106, Norway.
Camilla
C
Fritsvold
Department of Pathology, Norwegian Veterinary Institute, Oslo, NO-0106, Norway.|Department of Basic Sciences and Aquatic Medicine (Basam), Norwegian University of Life Sciences, P.O. Box 8146, Dep, N-0033, Oslo, Norway.
Trygve T
TT
Poppe
Department of Ocean Sciences, Memorial University, St. John's, NF, A1C5S7, Canada.
Matthew L
ML
Rise
Fisheries and Oceans Canada, Pacific Biological Station, 3190 Hammond Bay Rd, Nanaimo, BC, V9T6N7, Canada.
Kyle A
KA
Garver
Fisheries and Oceans Canada, Pacific Biological Station, 3190 Hammond Bay Rd, Nanaimo, BC, V9T6N7, Canada.
Stewart C
SC
Johnson
D000818:Animals; D019295:Computational Biology / Q000379:methods; D004198:Disease Susceptibility; D005393:Fish Diseases / Q000235:genetics* / Q000821:virology*; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D059014:High-Throughput Nucleotide Sequencing; D029142:Infectious hematopoietic necrosis virus; D007668:Kidney / Q000378:metabolism* / Q000821:virology; D012474:Salmon / Q000235:genetics* / Q000821:virology; D015163:Superinfection; D059467:Transcriptome
De novo assembly; Piscine reovirus, Infectious hematopoietic necrosis virus; RNA-seq; Sockeye salmon; Transcriptome