Coho salmon (Oncorhynchus kisutch) transgenic for growth hormone (Gh) express Gh in multiple tissues which results in increased appetite and continuous high growth with satiation feeding. Restricting GH-transgenics to the same lower ration (TR) as wild-type fish (WT) results in similar growth, but with the recruitment of fewer, larger diameter, muscle skeletal fibres to reach a given body size. We used RNA-seq to compare the skeletal muscle transcriptome in TR and WT coho salmon, an experimental model that uncouples the growth hormone and nutritional signals regulating growth. Illumina sequencing of libraries from 6 WT and 6 TR coho salmon yielded 704,550,985 paired end reads which were assembled into 323,115 contigs representing 16,000 unique genes of which >8,000 contained >90% of the coding sequence. Transcripts coding for 53 genes required for myoblast fusion were identified with 16 significantly downregulated in TR relative to WT fish, including 10 (vasp, cdh15, graf1, crk, crkl, dock1, trio, plekho1a, cdc42 and dock5) associated with signaling through the cell surface protein cadherin. 16 out of 46 (34%) translation initiation factors and 16 from 50 (32%) protein chaperones were upregulated in TR relative to WT fish. TR coho salmon showed increased growth hormone transcripts and gene expression associated with protein synthesis and folding than WT fish even though net rates of protein accretion were similar. The uncoupling of Gh and amino acid signals therefore resulted in additional costs of protein synthesis, which were compounded by increased activity levels. TR fish showed a downregulation of genes in multiple signaling pathways controlling myoblast fusion and increased average fibre size which is expected to produce compensatory energy savings in the cost of maintaining ionic homeostasis.
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