Tissue and Disease Specific Expression of miRNA Genes in Atlantic Salmon

Introduction: miRNAs are an abundant class of endogenous small RNA molecules that downregulate target gene expression at the posttranscriptional level. They play important roles in multiple biological processes by regulating genes that control e.g. developmental timing, growth and apoptosis by binding to the mRNA of target genes. We have recently characterized miRNA genes in Atlantic salmon. This has allowed further studies of miRNA expression and their association with tissue and disease state.

Materials and methods: Expression of miRNAs was analysed using global miRNA profiling (Illumina small RNA sequencing) and a miRNA-qPCR method dedicated for analyzing expression of individual salmon miRNAs. Expression levels were analysed in tissues from kidney, head kidney, gills, heart, liver, intestine, brain and white muscle as well as kidney/head kidney infected with the following virus’; ISAV, IPNV, SAV and PRV.   

Results: The miRNA expression profiles and subsequent validations by qPCR showed tissue specific expression of particular miRNA genes in liver, heart, intestine, gills and brain. The analyses of tissues from fish with viral disease revealed association between viral disease and several miRNA genes. Most of these miRNA genes have been shown to participate in innate immunity gene pathways in vertebrates. Details about the miRNAs identified as well as their putative function and target genes are presented.

Conclusion: The identification of particular miRNAs that show tissue specific expression or are associated with viral infection is a first step to better understand the role of miRNAs in regulation of tissue specificity and response to viral disease in Atlantic salmon.