Interaction of growth hormone overexpression and nutritional status on pituitary gland clock gene expression in coho salmon, Oncorhynchus kisutch

Abstract

Clock genes are involved in generating a circadian rhythm that is integrated with the metabolic state of an organism and information from the environment. Growth hormone (GH) transgenic coho salmon, Oncorhynchus kisutch, show a large increase in growth rate, but also attenuated seasonal growth modulations, modified timing of physiological transformations (e.g. smoltification) and disruptions in pituitary gene expression compared with wild-type salmon. In several fishes, circadian rhythm gene expression has been found to oscillate in the suprachiasmatic nucleus of the hypothalamus, as well as in multiple peripheral tissues, but this control system has not been examined in the pituitary gland nor has the effect of transgenic growth modification been examined. Thus, the daily expression of 10 core clock genes has been examined in pituitary glands of GH transgenic (T) and wild-type coho salmon (NT) entrained on a regular photocycle (12L: 12D) and provided either with scheduled feeding or had food withheld for 60 h. Most clock genes in both genotypes showed oscillating patterns of mRNA levels with light and dark cycles. However, T showed different amplitudes and patterns of expression compared with wild salmon, both in fed and starved conditions. The results from this study indicate that constitutive expression of GH is associated with changes in clock gene regulation, which may play a role in the disrupted behavioural and physiological phenotypes observed in growth-modified transgenic strains.

• Circadian rhythm
• clock genes
• coho salmon
• growth hormone
• pituitary gland
• transgenic

Acknowledgements

The authors thank Janice Oakes for valuable assistance with tank setup and assisting with sampling throughout the experiment.

Declaration of interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the article.

The authors acknowledge the financial support of the Canadian Regulatory System for Biotechnology to RHD.