Characterisation and differential expression of Atlantic salmon, Salmo salar, corticosteroid receptor paralogues following poly I:C and Vibrio anguillarum stimulations.

Farmed Atlantic salmon (Salmo salar) experience stressors throughout their growth including handling, transportation, and exposure to a diversity of pathogens, which triggers the release of cortisol. Cortisol mediates the effects of stress on many physiological processes within Atlantic salmon, including the immune response. The binding of cortisol to corticosteroid receptors, namely glucocorticoid (GR) and mineralocorticoid (MR) receptors, leads to cortisol mediated transcriptional modulation. The Atlantic salmon genome has experienced recent whole genome duplication resulting in multiple corticosteroid receptor paralogues: four GR and two MR. Currently, it is not known whether there is structural and functional divergence between GR and MR paralogues in driving cortisol-mediated immune modulation. We have addressed this by investigating GR and MR sequence divergence and transcriptional modulation in Atlantic salmon tissues following stimulation with a viral mimic (poly I:C) or heat-killed Vibrio anguillarum. GR and MR paralogue-specific expression changes were found to be tissue-type and immune stimulant-dependent, suggesting GR and MR paralogues may have distinct roles in the crosstalk between stress and immune responses. These results further our understanding of the impacts of stress on the immune function of Atlantic salmon and demonstrate the importance of exploring receptor paralogues and their function in greater depth.