Experts estimated the work could lead to the first animal-human transplants within five years.
The breakthrough came after scientists were able to remove a section of pig DNA, which had made the pig organs incompatible with human blood.
Previous attempts to combine unmodified pig lungs and human blood ended abruptly two years ago when blood clots began forming almost immediately, causing the organs to become so blocked no blood could pass through.
Human DNA is now added to the pigs as they are reared to reduce clotting and the number of lungs which are rejected.
Phytase produced in the salivary glands and secreted in the saliva increases the digestion of phosphorus contained in feed grains.
Enviropigs would then need approval from Health Canada before the pigs enter the food market.
The Yorkshire pigs were developed by researchers in Ontario at the University of Guelph, who spliced in genes from mice to decrease the amount of phosphorus produced in the pigs’ dung.
The genetic modification means the new strain of pigs produce 30 to 65 percent less phosphorus in their waste, which has been problematic in surface and groundwater around large livestock operations.
Enviropig is able to digest cereal grain phosphorus there is no need to supplement the diet with either mineral phosphate or commercially produced phytase, and there is less phosphorus in the manure. When the phosphorus depleted manure is spread on land in areas of intense swine production there is less potential of phosphorus to leach into freshwater ponds, streams and rivers. Because phosphorus is the major nutrient enabling algal growth that is the leading cause of fish kills resulting from anoxic conditions, and reduced water quality, the low phosphorus manure from Enviropigs has a reduced environmental impact in areas where soil phosphorus exceeds desirable levels. Therefore the enviropig biotechnology has two beneficial attributes, it reduces feed cost and reduces the potential of water pollution.
What is an Enviropig™?
Enviropig™ is a trademark used to designate a genetically modified (or genetically engineered) line of Yorkshire pigs that produces phytase in the salivary glands (parotid, submaxillary and sublingual), and secretes the enzyme in the saliva.
How does it work?
A transgene construct containing the murine (mouse) parotid secretory protein promoter gene sequence and the Escherichia coli phytase gene was introduced into the pig chromosome by pronuclear microinjection. This technique does not involve the use of either viral DNA or antibiotic resistance genes. The transgene construct was integrated in a single site in the genome, and shown to be stably transmitted to offspring in a Mendelian fashion through 8 generations. The promoter directs constitutive (continuous) production of the active phytase enzyme in secretory cells of the salivary glands including the parotid, submaxillary and sublingual glands. The phytase is secreted in the saliva and enters the mouth where it mixes with feed consumed. The phytase is most active in the acidic environment of the stomach (pH range of 2.0 to 5.5 during food consumption). There the enzyme digests the phosphorus rich phytate molecules releasing phosphate molecules that are readily absorbed from the small intestine.
The phytase is highly resistant to pepsin the major protease in the stomach, but is destroyed by trypsin and chymotrypsin in the small intestine and none is detected in the ileal contents. The phytase produced by the Enviropig™ is as active as the enzyme produced in Escherichia coli. There is only one protein produced from the transgene and that is the phytase enzyme.
How was an Enviropig™ created?
The Enviropig™ was developed by the introduction of a transgene construct composed of the promoter segment of the murine parotid secretory protein gene and the Escherichia coli phytase gene (Golovan et al 2001) into a fertilized porcine embryo by pronuclear microinjection, and this embryo along with other embryos was surgically implanted into the reproductive tract of an estrous synchronized sow. After a 114 day gestation period, the sow farrowed and piglets born were checked for the presence of the transgene and for phytase enzyme activity in the saliva. When the mature genetically modified pig was crossed with a conventional pig, approximately half of the pigs contained the phytase transgene. This showed that the transgene was stably inserted into one of the chromosomes of the pigs and was inherited in a Mendelian fashion. Through breeding, this line of pigs is in the 8th generation.