In 2013, scientists finished sequencing the pig genome, an achievement that promises to benefit not only the pig farming industry but also biomedical research. Pigs are already used to study certain human diseases. They are also being considered as potential organ donors for humans. These two areas of research will benefit greatly from researchers having the pig’s genetic information at their fingertips.
Did you know? Genetically modified pigs are not currently approved as a human food source. However, genetically modifying pigs for certain traits, like hairlessness (so the hair won’t have to be removed when processing pork), is being considered. Sequencing a genome involves analyzing all of a species’ genetic information and recording it as a sequence of letters—using A, C, G, and T to represent the four bases found in DNA.
So scientists now have a complete database for the pig genome, which is a bit like the maps app on your smartphone. But instead of finding restaurant locations, researchers can easily search for the locations of pig genes and quickly download DNA sequences, making their work both faster and easier.
The massive database contains a grand total of 2.6 billion letters, although it’s the order (sequence) of those letters that’s most important to scientists.
Move over mouse! Make room for the pig in biomedical research
Mice are commonly used to study human diseases, especially by genetic researchers. Since mice are mammals, they have almost all the same genes as you. After the sequence of the mouse genome was made available in 2002, it became much easier for researchers to to genetically modify mice to mimic human diseases. Furthermore, mice take up little space and breed quickly. All these characteristics make mice an attractive choice as laboratory animals for medical research.
Did you know? Pigs typically have 20 pairs of chromosomes, compared to 23 in humans. As a result, the pig genome contains 7% less DNA than the human genome. Obviously, because they are much larger than mice, it is more expensive to house pigs in a research facility. However, pigs share even more physical characteristics with humans, which makes them an even better choice for studying certain human diseases and conditions—such as cystic fibrosis, atherosclerosis, diabetes, obesity and blindness—as well as for developing and testing treatments.
When comparing DNA, humans share three times more similarities with pigs than with mice. Thanks to the sequencing of the pig genome, researchers can now use more precise genetic engineering methods to produce genetically modified pigs that will make it even easier to study human disease.
From heart valves to lungs: Harvesting pig organs for humans
Pigs are more than just a useful animal model for studying human disease. They could also be used for xenotransplantation (transplantation from one species to another). Since human organ donors only supply a fraction of the demand, researchers are looking to pigs as a potential source of organs.
In fact, pig organs are very close in size to human organs. Pig heart valves, which contain no live pig cells, are already used in humans. However, pig organs would be rejected by the human body. In the future, this problem could potentially be overcome by genetically engineering pigs so their tissues are not detected as foreign by the human immune system.
Did you know? The dog and cat genomes are 14% smaller than the human genome. Another risk already identified by researchers is the possibility that certain viruses hidden in the DNA of pig tissues, called porcine endogenous retroviruses (PERVs), could become active and infect human recipients of pig organs. They could also potentially spread to other people. The risk is considered low since PERVs have never been found to infect humans or other animals. However, they can infect human cell cultures grown in a laboratory. The risk of transmission could also be reduced by selecting pigs with lower amounts of the virus, through antiviral treatment of pigs, and through close monitoring of human recipients.
The idea of using animals in medical research and especially breeding animals to harvest their organs also raises important ethical questions. These questions tend to be more difficult in the case of animals that are considered more intelligent, more human-like, and more capable of feeling pain. For example, the use of mice tends to be less controversial than the use of pigs, and the use of pigs tends to be less controversial than the use of primates, such as monkeys.
Nevertheless, primates are already widely used in medical research. They are actually being used to test the safety of pig organ xenotransplantation. The fact that pigs are already farmed for meat is another interesting consideration. What do you think about using different species in medical research?
It’s too early to tell exactly what role pigs (and their organs) will play in human medicine. But one thing is certain: Thanks to the sequencing of the pig genome, biomedical research has a new star, the pig.
- Cooper DKC. 2012. A brief history of cross-species organ transplantation. Baylor University Medical Center Proceedings. 25(1):49-57. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3246856/
- Denner J, Ronjes RR. 2012. Infection Barriers to Successful Xenotransplantation Focusing on Porcine Endogenous Retroviruses. Clinical Microbiology Reviews. 25(2):318-343.