Identification, characterization, and transcription of serotonin receptors in rainbow trout (Oncorhynchus mykiss) in response to bacterial infection and salinity changes

Abstract

Serotonergic system is involved in the regulation of physiological functions and behavioral traits including cognition, memory, aggression, stress coping, appetite and immunomodulation. Serotonin exerts its functions via binding distinct serotonin receptors which are classified into 7 groups. Salmonid exhibits expanded functional gene copies due to salmonid-specific whole genome duplication. However, serotonin receptor (htr) repertoire is not fully identified in rainbow trout (Oncorhynchus mykiss). In this study, we identified 39 htr genes, including 14 htr1, 4 htr2, 4 htr2 like, 3 htr3, 4 htr4, 2 htr5, 2 htr6, and 6 htr7 subtypes. We investigated physiological functions of serotonin receptors in response to bacterial pathogens exposure and salinity changes. We showed htr1, htr2, htr4 and htr7 subtypes were associated with immunomodulation in response to Vibrio anguillarum or Aeromonas salmonicida infection. Saltwater (salinity of 15) transfer significantly altered htr1, htr2, htr4, and htr7 subtypes, suggesting trout Htr was associated with osmoregulation. We further showed residues interacted with inverse agonist (methiothepin) and serotonin analogue (5-Carboxamidotryptamine) were conserved between trout and human, suggesting exogenous ligands targeting human HTRs might have a role in aquaculture. This study showed duplicated trout Htrs might be physiologically neofunctionalized and potentially exhibit pleiotropic effects in regulating immunomodulation and osmoregulation.