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Green-tinged farm points the way

Pigs and chickens that glow in the dark may signal a new era for the farm yard.

UK scientists at the Roslin Institute say they have dramatically improved the technique for introducing modifications to an animal's genetic make-up.

So far, the researchers have used the new method to introduce a jellyfish gene that makes their pigs and chickens fluoresce - to prove changes will work.

Now, the scientists expect to create animals that are resistant to disease or can be used to study disease.

The Edinburgh institute described its latest research to BBC Radio 4's One Man's Meat programme.

Piggyback research

Conventional efforts to make so-called transgenic animals have been expensive, hampered by inefficient methods of production, which see only about one in 70 embryos injected with genetic material resulting in a modified animal.

The improved technique borrows from procedures developed for gene therapy in humans.

In one of several recent trials at the Roslin Institute, the new approach resulted in 36 out of 40 pig embryos developing into transgenic pigs.

That is a success rate of 90% and has the power to revolutionise the application of GM technology in farm animals, according to researchers Dr Bruce Whitelaw and Dr Helen Sang.

The new technique uses viruses to carry chosen genes into fertilised eggs. Once altered, the eggs are then implanted in surrogate females.

The viruses come from a family called lentiviruses which have undergone extensive medical research.

"We're now piggybacking on this medical research as a way of producing transgenic animals, and what makes these vectors exciting is the fact that they're very efficient," said Dr Whitelaw, from Roslin's department of gene expression and development.

"Rather than the minority of animals ending up transgenic, the majority end up transgenic."

Asian flu

Transgenic pigs and chickens have been produced at Roslin using lentivectors to carry the green fluorescent protein gene (GFP) - a gene found naturally in jellyfish.

Both chickens and pigs carrying the gene can be detected in normal light by their slight greenish tinge, but when viewed in blue light, all areas not covered with hair or feathers are seen to glow torch-light bright.

In the case of chickens, this is the feet and head; and in pigs, it is the ears, snout, trotters and testicles.

"The green fluorescent protein marker gene means we can see instantly if an animal is carrying the gene; there is no need for any biopsies or tests, and as far as we know all of the animals are normal in every other way," said Dr Whitelaw.

Three generations of chickens carrying the GFP have now been produced, showing consistent and stable gene expression.

Poultry researcher Dr Sang is now ready to test the technique with genes of research interest.

"At the moment, we're trying to produce hens with pharmaceutical proteins in their eggs.

"We're looking at a therapeutic protein for cancer treatment," she said, "but we've also now got funding to look at two poultry diseases: Marek's disease and Asian flu."

The technique is most likely to be used to create transgenic animals to study diseases but might also eventually be used to make farm animals that are resistant to specific diseases.

"If you want to make transgenics, you need to be able to make lots of different lines to check them. We couldn't do that until now. It's a much easier and simpler approach.

"These techniques are proving 10 to 100-fold more efficient than any of the old techniques," Dr Sang said.

Posted by thinkum at April 29, 2004 01:18 PM