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Unintended Effects of Genetic Manipulation
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Transgenic pigs with elevated levels of growth hormone were infertile, pre-diabetic, and experienced joint problems.

Manipulated Organism: Pig (Sus domesticus).

Inserted Transgenes: Pig growth hormone (GH) gene, with expression controlled by either the human cytomegalovirus (CMV) or mouse leukemia virus (MLV) promoter.

Goal of This Study: Monitor the development of the transgenic pigs.

Results of This Study:
  • Transgenic DNA was injected into 1094 one- or two-celled embryos taken from pigs and then re-implanted in 30 animals. Seventeen of these pigs maintained their pregnancy and delivered 124 piglets, of which 31 contained the transgene.

  • The 31 transgenic offspring contained anywhere from 1 to 20 copies of the transgene, and in one case the transgene had mutated.

  • Elevated levels of growth hormone (GH) were only detected in the blood of 3 out of 31 transgenic animals.

  • The two different promoters used in the study led to very different patterns of gene expression. In the pig with the CMV promoter, transgene expression appeared to be localized to the pancreas, while in the pig with the MLV promoter, transgenic RNA was detected in the pituitary, stomach, intestine, spleen, and lymph nodes.

  • The transgenic pigs with elevated GH levels did not gain weight more rapidly than is typical of non-GM pigs, but their carcassess were much leaner (5 versus 25 mm of backfat). The pigs also appeared to be infertile (did not show estrous behavior), had high levels of insulin in their blood (indicating insulin resistance), and suffered from joint problems.

Source: Ebert, K. M., T. E. Smith, F. C. Buonomo, E. W. Overstrom et al. (1990). "Porcine Growth Hormone Gene Expression from Viral Promoters in Transgenic Swine," Animal Biotechnology vol. 1, pp. 145-59.

Author Affiliations: Tufts University, MA; Monsanto Co., MO; New England Medical Center Hospital, MA.

Funding: Monsanto Co.; Tufts University School of Veterinary Medicine.

Product Status: Not on the market as of 2009.

Copyright 2009 The Nature Institute.

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