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Unintended Effects of Genetic Manipulation
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Transgenic expression of a mouse milk protein impaired mammary development and function in pigs.

Manipulated Organism: Pig (Sus domesticus).

Inserted Transgenes: Mouse genomic DNA containing the gene for whey acidic protein (WAP).

Goal of These Studies: Investigate the feasibility of using mouse WAP regulatory sequences to produce transgenic proteins in the milk of pigs.

Results of This Study:
  • In 3 of the 5 lines of transgenic pigs, lactation was impaired in some animals. The problems were discovered when, after 10 days of nursing, piglets started to lose weight.

  • Pigs from the other 2 transgenic lines appeared to lactate normally, and the transgenic WAP protein was discovered in their milk. However, one of these animals produced an unknown form of the WAP protein, which the authors speculated could be "the result of some rearrangement within the transgene locus" (p. 4558). The amount of this unexpected protein decreased over time, while the amount of normal WAP protein increased over the course of the lactation.

  • Mammary tissue from the transgenic pigs, even those with apparently normal lactations, had abnormal morphology, indicative of immature development.

  • Precocious WAP gene expression was detected in five-month-old juvenile pigs from the lactation-impaired lines, but not in pigs from the lactation-competent and non-GM lines.

Source: Shamay, A., V. G. Pursel, E. Wilkinson, R. J. Wall et al. (1992). "Expression of the Whey Acidic Protein in Transgenic Pigs Impairs Mammary Development," Transgenic Research vol. 1, pp. 124-32.

Shamay, A., S. Solinas, V. G. Pursel, R. A. McKnight et al. (1991). "Production of the Mouse Whey Acidic Protein in Transgenic Pigs During Lactation," Journal of Animal Science vol. 69, pp. 4552-62.

Author Affiliations: National Institutes of Health; ETH-Zentrum, Switzerland; USDA Agricultural Research Service, Maryland; University of Illinois, Chicago; University of Tennessee College of Veterinary Medicine.

Funding: Not mentioned.

Product Status: Not on the market as of 2009.

Copyright 2009 The Nature Institute.

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