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Unintended Effects of Genetic Manipulation
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Transgenic expression of growth hormone in coho salmon led to a narrower body, more red muscle mass, and smaller white muscle fibers.

Manipulated Organism: Coho salmon (Oncorhynchus kisutch).

Inserted Transgenes: Type I salmon growth hormone gene.

Goal of This Study: Compare the muscle anatomy, physiology, and gene expression of transgenic salmon with non-GM relatives of similar size. Because the transgenic salmon grow more rapidly, the size-matched non-GM salmon were one year older.

Results of This Study:
  • Despite having comparable total body weight and length, the transgenic fish had narrower bodies. The cross-sectional area of the transgenic fish at mid-length was 75% the area of the non-GM fish. Additionally, the abdominal wall of the GM fish was only half as thick.

  • There are two types of skeletal muscle in animals: red and white, specialized for sustained versus rapid activity, respectively. The amount of red muscle in the tail of the GM fish was twice that in the non-GM fish (2% vs. 1% red, p < 0.01).

  • The white fibers of the GM fish were half as wide, indicating that muscle development had changed to emphasize the proliferation of new cells (hyperplasia) over the growth of existing cells (hypertrophy).

  • The specific activity of phosphofructokinase (PFK), a key enzyme in the utilization of glucose and critical to muscle function, was over three times higher in the transgenic fish (p < 0.01).

Additional Comments: "In conclusion, increased growth rates, caused by transgenesis, in coho salmon have resulted in changes to muscle architecture consistent with increased rates of hyperplasia [cell proliferation]. This identifies a meat quality effect of growth rate that can be considered in future studies. Changes in levels of the muscle enzymes PFK and Cytox suggest effects on metabolism that can also lead to changes in meat quality due to postmortality effects" (p. 949).

Source: Hill, J. A., A. Kiessling, and R. H. Devlin (2000). "Coho Salmon (Oncorhynchus kisutch) Transgenic for a Growth Hormone Gene Construct Exhibit Increased Rates of Muscle Hyperplasia and Detectable Levels of Differential Gene Expression," Canadian Journal of Fisheries and Aquatic Sciences vol. 57, pp. 939-50.

Author Affiliations: Fisheries and Oceans Canada, West Vancouver; Swedish University of Agricultural Sciences.

Funding: Fisheries and Oceans Canada; Swedish University of Agricultural Sciences.

Product Status: Not on the market as of 2009.

Copyright 2009 The Nature Institute.

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