Two research groups reported successfully cloning pigs last week, using two different variations of the technique used to clone Dolly the sheep. A team based at the National Institute of Animal Industry, Japan, published details of the method it used to clone a pig - called Xena - from an embryo cell in last week's Science. And Nature has published a paper from a team at PPL Therapeutics Ltd on its website, which describes the cloning of five pigs from adult cells. The birth of the PPL piglets was announced to the press back in March, but the print version of the report has yet to be published.
The announcements have implications for research into xenotransplantation - the use of pig organs for human transplants. But such pigs would first have to be genetically modified, to prevent the human body rejecting the animal tissue. Scientists are concentrating on knocking out the pig gene that makes the GLINK(#:2312, enzyme)} 1,3-galactosyl transferase. This enzyme makes alpha-1,3-galactose, a sugar, which is the main target for rejection by the human immune system. However, even if this problem can be overcome, there are still worries over possible infection by pig viruses.
Pigs have proved more difficult to clone than other mammals, such as sheep, goats and cows. This is partly because at least four healthy embryos must be present to sustain a pregnancy in a female pig. But the two teams of researchers also had to make changes to the method used to the 'Dolly method', in which an adult body cell was fused with a donor eggs tripped of its own genetic material. The Japanese group injected the genetic material directly into the donor egg, a technique used to create the world's first cloned mouse.
The PPL team used a method dubbed 'double nuclear transfer' to clone its piglets, in which the cloned genetic material is transferred from the donor egg into the 'shell' of a fertilised egg. 'It's a bit more labour intensive, but if you look at our success rate it's a more efficient method' said Ron James, managing director of PPL.
Sources and References
Scientists propose two ways to clone a pig
Pig cloning breakthrough but virus fears may delay organ transplants
Xena: a new generation