SRA

Betanodaviruses (VNNV) are the causative agents of the viral nervous necrosis, a disease that affects cultured Senegalese sole (Solea senegalensis). VNNV reassortant strains, combining genomic segments from the RGNNV and SJNNV genotypes, have previously been isolated from wild and farmed several fish species. The wild reassortant wSs160.03 isolated from sole has been proved to be more virulent for sole than the parental genotypes (RGNNV and SJNNV), causing 100% mortality. Mutations of wSs160.03 strain performed by reverse genetic, have allow to obtain a mutant reassortant strain (rSs160.03247+270) with mutations at amino acids 247 (serine to alanine) and 270 (serine to asparagine), which provoke a 40% decreased mortality. In the current study, the RNA-Seq technology has been used to compare the Senegalese sole transcriptomes in two organs (head-kidney and eye/brain) after infection with the wild reassortant strain and the mutant reassortant strain. A total of 633 genes were differentially expressed (DEGs) in animals infected with the wSs160.03 strain, whereas only 393 genes were differentially expressed in animals infected with the rSs160.03247+270 strain, indicating a 37.9% decrease in the number of DEGs after infection with the mutated reassortant strain. An inversion in the proportion of genes up/down-regulated in nervous tissue of these animals was also obtained for both reassortants. To understand the biological functions of identified DEGs involved in VNNV infection, a gene ontology (GO) enrichment analysis was performed with fold change > 1.5 (up- or down-regulated) and p-value < 0.05. Different profiles of GO were obtained in the subclasses biological process, cellular component, and molecular function for each reassortant strains. Regarding the immune response, genes coding for proteins acting as mediators of IFN type I expression (DHX58, IRF3, IRF7) and IFN-stimulated genes (ISG15, Mx, PKR, Gig1, ISG12, IFI44, IFIT-1, to name a few) were up-regulated in animals infected with the wild type reassortant, whereas no-differential expression of these genes was observed in animals infected with the mutant reassortant. The different transcriptomic profiles obtained could help to better understand VNNV pathogenesis in Senegalese sole, setting up the importance as virulence determinants of amino acids at positions 247 and 270 within the RNA2 segment. Overall design: Evaluation of amino acid positions 247 and 270 of the capsid protein as virulence determinants of VNNV.