In 1997, Dhani Ram Baruah, a cardiac surgeon in Assam tried to transplant the heart and lungs of a pig into a patient. The patient died and Baruah was arrested for breaking the law governing human transplantation. Despite the fact that pigs provide pharmaceutical-grade heparin and heart valves for transplantations, whole organ transplantation between different animals usually fail due to genetic incompatibility.
At that time, the genome of neither man nor pig was known. While human genome was deciphered in 2003, two studies published on November 14 provide some insight into pigs’ genome. Although it cannot be said if the information would have helped Baruah’s patient, the researchers claim the studies provide crucial data for improving pig stock and biomedical research.
|What the two studies found
- Physiology of the Wuzhishan pigs and humans is 84 per cent similar at the genetic level
- While genes involved in coronary artery disease were very much alike in humans and pigs, there are several important differences that need to be taken into account in future research
- The studies identified 112 positions in the genome where pig protein has the same amino acid that is implicated in a human disease. This supports the use of pig in studies on human diseases
- Comparisons between domestic and wild pigs revealed that European and Asian breeds were distinct, suggesting the pigs were domesticated independently in western Eurasia and East Asia
- The pig has more unique olfactory genes than humans, mice or dogs. This means that while pigs can smell things humans and other animals cannot, their sense of taste does not keep up and they end up eating everything
The studies have been published in Nature and GigaScience. The Nature study by the Swine Genome Sequencing Consortium presents the genome of wild boar and domestic pig, an economically important breed. The GigaScience study, led by researchers from the BGI (a global collaboration on genomic research), Beijing Institute of Animal Science and Chinese Academy of Agriculture Science, focuses on a miniature pig used in medical research.
The miniature Wuzhishan pig is extensively inbred and individuals are genetically similar. Its small size makes it easy to handle and useful for medical research. The team looked at genes and protein domains that pigs and humans share. These are important targets for drugs. The researchers found the physiology of the two is 84 per cent similar at the genetic level.
But they also noted that while genes involved in coronary artery disease were very much alike in humans and pigs, there were several important differences that need to be taken account of in future research. On the positive side, the research showed that the miniature pig does not have hidden viruses in its genome. These viruses get transferred to humans during xenotransplantation or transplantation of organs or parts of organs from one species to another. The finding, thus, shows that Wuzhishan pig is a viable research material.
For the study published in Nature, researchers compared the genome of domestic pig with that of wild boar. They collected wild boar genome samples from different parts of Europe and Asia. They found that the Asian and European wild boars had significant genetic differences. This, they say, possibly happened when the two separated from each other roughly one million years ago. Comparisons between domestic and wild pigs also revealed that European and Asian breeds were distinct, suggesting the pigs were domesticated independently in western Eurasia and East Asia.
The results also show that some gene families are evolving faster in domestic pig. These include olfactory genes and genes that confer immunity. The pig has more unique olfactory genes than humans, mice or dogs. This means that while pigs can smell things humans and other animals cannot, their sense of taste does not keep up and they end up eating everything. Pigs have fewer bitter taste receptor genes than those involved in perception of sweet and umami flavours. Also, the bitter taste receptor genes in pigs are lesser in number than those in humans.
The studies identified 112 positions in the genome where pig protein has the same amino acid that is implicated in a human disease. This supports the use of pig in studies on human diseases. Some of the protein aberrations that pigs share with humans are associated with obesity, diabetes, dyslexia, Parkinson's disease and Alzheimer's disease. This understanding of the genetic origins of modern pigs is important for their breeding and to find new ways to deal with old and emerging diseases.