Cloning of mice confirms Dolly's pedigree

Confirmation that researchers have cloned three generations of mice, all of 22 offspring with exactly the same genetic make-up, has shifted animal cloning on to a surer, probably more controversial plane. For those associated with the cloning of Dolly the sheep, the news helps prove their ground-breaking achievement was not a fluke.

An international team at the University of Hawaii created the female mice copies, details of which were published yesterday in the scientific journal, Nature. The team shows cloning using adult cells can be done.

Any lingering doubts were eliminated by additional findings of a team including the founder of genetic fingerprinting, Sir Alec Jeffreys, indicating "beyond reasonable doubt" that Dolly was what her makers at the Roslin Institute in Scotland said she was: derived from an adult cell.

The development (using a technique different to that used by Dr Ian Wilmot and his team at Roslin) makes it possible to step up research because mice are bred more quickly than sheep.

Once the technique devised by the Dr Ryuzo Yanagimachi-led team in Hawaii is perfected, it could lead to new cancer therapies, improvements in agricultural production, in the making of drugs, and with research into AIDS, diabetes and ageing.

It involves taking DNA from the cell of a female adult and injecting it into an egg from which the DNA has been removed. The artificially fertilised egg is inserted into a surrogate mother, and the clone produced. They used a different type of cell, taken from the part of the ovary surrounding the egg and called a cumulus cell.

The team in Honolulu will work with PPL Therapeutics, the commercial side of the Roslin operation, which is already involved in using genetically engineered sheep to make human proteins, it has been announced.

Before March 1997, it was suggested such cloning was a biological impossibility (with some scientists insisting the biological clock could not be turned back), but Dolly - an exact copy of an adult - changed all that in addition to raising ethical concerns and the spectre of human cloning. Yet speculation grew that Dolly was not as claimed, and the achievement could not be repeated.

Most speculation centred on the possibility that Dolly's parent had been pregnant at the time and that, against huge odds, the researchers had used a foetal cell which had made its way into the sheep's udder. Repeated failures to clone mice using the Dolly technique of nuclear transfer heightened speculation.

Moreover, the technique is achieving a success rate of one in 40 cases, compared to one in 277 with the Dolly technique.

--(Additional reporting by Guardian Service)