What is a genetically engineered animal?
A genetically engineered or “transgenic” animal is an animal that carries a known sequence of recombinant DNA in its cells, and which passes that DNA onto its offspring. Recombinant DNA refers to DNA fragments that have been joined together in a laboratory. The resultant recombinant DNA “construct” is usually designed to express the protein(s) that are encoded by the gene(s) included in the construct, when present in the genome of a transgenic animal. Because the genetic code for all organisms is made up of the same four nucleotide building blocks, this means that a gene makes the same protein whether it is made in an animal, a plant or a microbe. Some examples of proteins that have been expressed in transgenic animals include therapeutic proteins for the treatment of human diseases1-4, proteins that enable animals to better resist disease5-7, and proteins that result in the production of more healthful animal products (milk, eggs or meat) for consumers8,9.
Are there any genetically engineered animals on the market?
As of August 2008, no genetically engineered food animals had been approved for sale in the United States. Growth-enhanced fish are the transgenic animal application closest to commercialization for food purposes, and several different species are currently going through regulatory review in three different countries. Since 1999, Aqua Bounty (Aqua Bounty Technologies Inc., Waltham, MA) has been seeking U.S. regulatory approval for the commercialization of its growth-enhanced AquAdvantageTM Atlantic salmon. This transgenic salmon is capable of growing faster, but not larger, than standard salmon grown under the same conditions10,11. Transgenic lines of growth-enhanced tilapia and carp are also under regulatory review in Cuba and China, respectively12. The only genetically engineered animal to reach the market in the United States is an ornamental fluorescent zebrafish (Danio rerio) called GloFish (Yorktown Technologies, Austin, TX). The U.S. Food and Drug Administration (FDA) determined not to formally regulate GloFish on the basis that tropical zebrafish pose no threat to the food supply, and the fact that there is no evidence that these genetically engineered zebrafish pose any greater threat to the environment than their widely sold unmodified counterparts13.
Figure 1. Genetically engineered zebrafish. Picture taken from www.glofish.com
One product of genetic engineering that is currently being used in animal agriculture is recombinant bovine somatotropin (rBST) derived from genetically engineered bacteria. This protein, which results in an increase in milk production when administered to lactating cows, is widely used throughout the U.S. dairy industry. rBST was approved by the FDA in 1993 because extensive testing had revealed no concerns regarding the safety of milk derived from cows treated with rBST14. It should be noted that administering this protein does not modify the DNA of the cow, and they do not become genetically engineered. People with diabetes similarly administer themselves with insulin derived from genetically engineered bacteria, and the genetic makeup of these patients is likewise unaltered by the administration of a recombinant protein.