Global gene expression responses of Atlantic salmon skin to Moritella viscosa

Abstract

Moritella viscosa is a Gram-negative pathogen that causes large, chronic ulcers, known as winter-ulcer disease, in the skin of several fish species including Atlantic salmon. We used a bath challenge approach to profile the transcriptome responses of M. viscosa-infected Atlantic salmon skin at the lesion (Mv-At) and away from the lesion (Mv-Aw) sites. M. viscosa infection was confirmed through RNA-based qPCR assays. RNA-Seq identified 5212 and 2911 transcripts differentially expressed in the Mv-At compared to no-infection control and Mv-Aw groups, respectively. Also, there were 563 differentially expressed transcripts when comparing the Mv-Aw to control samples. Our results suggest that M. viscosa caused massive and strong, but largely infection site-focused, transcriptome dysregulations in Atlantic salmon skin, and its effects beyond the skin lesion site were comparably subtle. The M. viscosa-induced transcripts of Atlantic salmon were mainly involved in innate and adaptive immune response-related pathways, whereas the suppressed transcripts by this pathogen were largely connected to developmental and cellular processes. As validated by qPCR, M. viscosa dysregulated transcripts encoding receptors, signal transducers, transcription factors and immune effectors playing roles in TLR- and IFN-dependent pathways as well as immunoregulation, antigen presentation and T-cell development. This study broadened the current understanding of molecular pathways underlying M. viscosa-triggered responses of Atlantic salmon, and identified biomarkers that may assist to diagnose and combat this pathogen.

Expression Analysis of Moritella viscosa-Challenged Atlantic Salmon Identifies Disease-Responding Genes, MicroRNAs and Their Predicted Target Genes and Pathways

“…In summary, the reproduced detection of M. viscosa -responding genes in this transcriptome study firmly establishes these genes, and those gene pathways where they were enriched, as important in response to winter-ulcer. The fact that the microarray analysis agreed very well with prior studies [ 35 , 36 , 37 ] also provide confidence that the investigation of miRNAs in same materials has the capacity to identify disease relevant miRNAs.…”

“…A study of expression changes in M. viscosa lesion materials applying RNA sequencing was recently reported [ 37 ]. There are several differences between the current study and this RNA seq study (e.g., sampling time points, LS sites sampled, application of two completely different platforms (RNA seq and microarray)) which could lead to different results due to study design.…”

“…In parallel, expression analysis was also carried out in head-kidney, which is an important immune organ in teleost fish. Unlike miRNAs, mRNAs responding to M. viscosa infection have been previously characterized in Atlantic salmon by microarray analysis or high-throughput sequencing [ 6 , 35 , 36 , 37 ]. The results of these studies (differentially expressed mRNAs) have been used as input in enrichment analyses to reveal biological processes that are affected by infection.…”

Influence of Supplemental Dietary Cholesterol on Growth Performance, Indices of Stress, Fillet Pigmentation, and Upper Thermal Tolerance of Female Triploid Atlantic Salmon (Salmo salar)

“…However, this hypothesis is quite speculative. Eslamloo et al [ 73 ] showed that hsp70 , hsp90aa1 , and cirbp transcript expressions were upregulated, while that of serpinh1 and ucp2 was downregulated, in the skin of ~200 g (8°C acclimated) diploid Atlantic salmon exposed to Moritella viscosa , whereas liver hsp70 , hsp90aa1 and ucp2 transcriptions were upregulated in ~500 g male diploid Atlantic salmon reared at 12 or 20°C and injected with a commercial multivalent vaccine (i.e., Forte Micro; containing formalin-inactivated cultures of several bacterial pathogens) (Ignatz et al, in prep.).…”