Coho salmon (Oncorhynchus kisutch) transgenic for a growth hormone gene construct exhibit increased rates of muscle hyperplasia and detectable levels of differential gene expression

Transgenic coho salmon (Oncorhynchus kisutch) containing a growth hormone gene construct were compared with nontransgenic coho salmon in terms of gross anatomy, muscle cellularity, muscle enzyme activity, and differential gene expression. Transgenic fish were found to have significantly higher numbers of small-diameter muscle fibres in both the dorsal and lateral region of the somitic muscle, suggesting that they grow by greater rates of hyperplasia relative to slower growing nontransgenic fish. Higher levels of activity were found for phosphofructokinase and cytochrome oxidase in white muscle of the transgenic fish. This difference indicates a higher glycolytic and aerobic requirement in the muscle of transgenic fish. Subtractive hybridisation of muscle RNA of transgenic fish from control fish provided a library of cDNAs whose expression is upregulated in the transgenic fish. This library contains genes that may be involved in, or related to, both high growth rates and muscle hyperplasia. We have sequenced a number of fragments and have found a preponderance of myosin light chain 2 mRNAs, consistent with a putative high level of expression in the early stages of muscle fibre construction.