Effect of growth rate on transcriptomic responses to immune stimulation in wild-type, domesticated, and GH-transgenic coho salmon

Abstract

RNA-Seq was performed on liver and head kidney in four 'growth response groups'injected with polyinosinic-polycytidylic acid (Poly I:C; viral mimic), peptidoglycan (PGN;bacterial mimic) or PBS (control). These groups were: 1) 'W': wild-type, 2) 'TF': growth hormone (GH) transgenic salmon with ~3-fold higher growth-rate than W, 3) 'TR': GH transgenic fish ration restricted to possess a growth-rate equal to W, and 4) 'D': domesticated non-transgenic fish showing growth-rate intermediate to W and TF. D and TF showed a higher similarity in transcriptomic response compared to W and TR. Several immune genes showed constitutive expression differences among growth response groups, including perforin 1 and C-C motif chemokine 19-like. Among the affected immune pathways, most were up-regulated by Poly I:C and PGN. In response to PGN, the c-type lectin receptor signalling pathway responded uniquely in TF and TR. In response to stimulation with both immune mimics, TR responded more strongly than other groups. Further, group-specific pathway responses to PGN stimulation included NOD-like receptor signalling in W and platelet activation in TR. TF consistently showed the most attenuated immune response relative to W, and more DEGs were apparent in TR than TF and D relative to W, suggesting that a non-satiating ration coupled with elevated circulating GH levels may cause TR to possess enhanced immune capabilities. Alternatively, TF and D salmon are prevented from acquiring the same level of immune response as TR due to direction of energy to high overall somatic growth.