In many vertebrate species visible melanin-based pigmentation patterns correlate with high stress- and disease-resistance, but proximate mechanisms for this trait association remain enigmatic. Here we show that a missense mutation in a classical pigmentation gene, melanocyte stimulating hormone receptor (MC1R), is strongly associated with distinct differences in steroidogenic melanocortin 2 receptor (MC2R) mRNA expression between high- (HR) and low-responsive (LR) rainbow trout (Oncorhynchus mykiss). We also show experimentally that cortisol implants increase the expression of agouti signaling protein (ASIP) mRNA in skin, likely explaining the association between HR-traits and reduced skin melanin patterning. Molecular dynamics simulations predict that melanocortin 2 receptor accessory protein (MRAP), needed for MC2R function, binds differently to the two MC1R variants. Considering that mRNA for MC2R and the MC1R variants are present in head kidney cells, we hypothesized that MC2R activity is modulated in part by different binding affinities of the MC1R variants for MRAP. Experiments in mammalian cells confirmed that trout MRAP interacts with the two trout MC1R variants and MC2R, but failed to detect regulation of MC2R signaling, possibly due to high constitutive MC1R activity.
KAUST Repository Item: Exported on 2020-10-01
Acknowledgements: We are deeply thankful to Tom Pottinger for making the HR-LR rainbow trout strains available for this study. We thank Jon K. Lærdahl for making a structural model of MC1R, Christina Sørensen for helping with the cortisol analysis and Ida G. Lunde for help with the figures. Primer and competitor design for the real competitive PCR analysis was kindly performed by Sequenom Custom Service, Hamburg, Germany. The project was financially supported by the Norwegian University of Life Sciences, by Research Council of Norway projects no. 172609, 199728, 218534 and by National Institutes of Health Grant DK19974 (P.M.H.). Atlantic Salmon genomic sequences used for primer design was kindly provided by the International Cooperation to Sequence the Atlantic Salmon Genome (ICSASG).