Researchers in Italy and Australia are to introduce 18 transgenic piglets to a meeting in California next week, in an attempt to convince sceptics that their disputed transgenic methodology does indeed work. They say that the technique could be a cheap and efficient way to produce animals expressing multiple foreign genes.

Marialuisa Lavitrano of the University of Milan-Bicocca, together with a group led by Ian McKenzie at the Austin Research Institute in Melbourne, created the animals, which express up to three foreign test genes, using a method called sperm-mediated gene transfer (SMGT).

Lavitrano first reported the method in 1989, when she found that sperm cells can internalize foreign DNA fragments, integrate the fragments' genes into their chromosomes, and then transfer these genes to the next generation during fertilization. But many laboratories were unable to repeat her results, probably because key factors — such as optimal incubation temperature and the time required for DNA integration — vary widely, even between animals of the same species.

Colour code: a pig embryo, seen through colour filters, reveals expression of three foreign genes. Credit: VETERINARY SCIENCE FACULTY, UNIV. BOLOGNA

Lavitrano hopes to win over the doubters when she discusses the piglets on 11 August at the Transgenic Animal Research Conference in Lake Tahoe, California. Together with her Australian colleagues, she transferred test genes encoding coloured proteins — green, red and blue — into sperm cells and used them to inseminate female pigs.

The technique was surprisingly successful: of more than 100 embryos created, 90% expressed all three genes. And when two of the sows gave birth in Bologna, Italy, on 20 April, seven piglets contained all three coloured proteins, another seven contained two, and the remaining four displayed one.

The results are “big news”, says Bob Wall, a researcher with the US Department of Agriculture in Beltsville, Maryland. SMGT — in the hands of Lavitrano and McKenzie, at least — has a better success rate than other, more widely used transgenic techniques, such as DNA micro-injection and nuclear transfer.

DNA micro-injection, which involves injecting DNA fragments into a fertilized egg, results in fewer than 1% of injected eggs giving rise to healthy animals expressing transgenes. And nuclear transfer, in which the nucleus of a genetically engineered adult cell is transferred to an egg cell whose nucleus has been removed, has an efficiency of 1–2% in livestock, and has not yet led to successful multiple gene transfer.

Animals expressing multiple foreign genes will be important in studying the feasibility of organ transplantation from pigs to people, says Lavitrano. Introducing a suite of genes to make pig organs more similar to those of humans could help to prevent their rejection by the recipient's immune system, she says.

But companies still doubt that SMGT will be commercially viable. Tom Newberry of Genzyme Transgenics Corporation in Framingham, Massachusetts, says that micro-injection and nuclear transfer are inefficient but more commercially attractive, as they do not require specific lab conditions for each animal.

“SMGT could be important for smaller laboratories that cannot afford to handle the large numbers of animals that inefficient methods require,” he adds.