Daily expression patterns of growth-related genes in growth hormone transgenic coho salmon, Oncorhynchus kisutch

Growth in fish is regulated by the growth hormone (GH)/ growth hormone receptor (GHR)/ insulin-like growth factor (IGF)-I axis. This GH-IGF-I axis is influenced by several factors. With regard to hormonal effect, it is known that salmon transgenic for GH show increased growth. However, very little is known about the expression patterns of growth-related genes in GH transgenic fish. The present study examined the daily expression patterns of mRNAs for the growth-related genes after feeding in GH transgenic coho salmon (Oncorhynchus kisutch). GH mRNA was detected in both liver and muscle as well as in the pituitary from transgenic fish. GHR mRNA levels in the liver and muscle were higher in transgenic fish than in non-transgenic wild type fish but lower in the pituitary. The expression level of hepatic IGF-I mRNA was greater in transgenic fish. The daily GH, GHR and IGF-I mRNA expression patterns reached their peak at roughly 4-8 h after feeding, however, GHR and IGF-I mRNA expressions in the liver was observed to be irregular in non-transgenic fish. These results suggest that the daily expression patterns for growth-related genes are particularly pronounced in GH transgenic fish. Furthermore, our findings would be useful for consideration of the time of feeding and the optimum time of day for tissue sampling for analysis of growth-related genes in fish.