Dolly the clone is no longer alone.
Resolving doubts about the authenticity of cloning, an international research team has produced three generations of cloned laboratory mice from adult cells, the group announced Wednesday. At the same time, two laboratories separately confirmed the unique genetic pedigree of the cloned sheep Dolly, whose creation triggered a worldwide furor.
Together, the new findings assure cloning a prominent role in the biology of the next century, experts said, but they do little to quiet international misgivings about the unprecedented control that the new technique promises over the ways that mammals--including human beings--reproduce themselves.
In research that may hasten the advent of commercial cloning, a group of Japanese, American and English researchers working at the University of Hawaii successfully cloned 50 animals from adult mouse cells, the scientists announced Wednesday. They used a new and perhaps more efficient cloning technique.
The team also demonstrated not only that their cloned mice can reproduce normally, like Dolly, but also that it is possible to create clones of clones by taking the new asexual reproduction technique of nuclear transfer through several generations without serious difficulty.
That finding--the first time clones have been produced from clones--means that "you can quite quickly make a colony of clones," said embryologist Anthony Perry of the Babraham Institute in Cambridge, England, one member of the research team.
Their research marks the first time anyone has demonstrably duplicated the controversial cloning experiment that produced Dolly--by reproducing an animal from the nucleus of a mature cell taken from an adult.
Until now, except for Dolly, researchers have succeeded only in cloning cattle and other livestock from cells taken from embryos or fetuses, not from adults. In part because no one had been able to repeat the experiment, several prominent biologists had argued that the famous sheep was not a biological breakthrough but a laboratory error.
In research published today in the journal Nature, the Honolulu-based team led by Ryuzo Yanagimachi, an expert in reproductive biology at the University of Hawaii, put those doubts about cloning to rest.
"It worked very beautifully," Yanagimachi said.
Robert J. Wall, an animal researcher with the U.S. Department of Agriculture, said, "The first and foremost aspect of this is that Dolly is not a fluke. Now the procedure of nuclear transfer has successfully produced offspring in another species using another kind of cell with a slightly different technique."
"I don't think there is going to be much in the way of questions whether Dolly is real," Wall said.
"The importance of this report cannot be overemphasized," said developmental biologist Davor Solter at the Max Planck Institute in Freiburg, Germany.
For the researchers most directly involved in cloning Dolly, the relief was audible.
Ian Wilmut, the embryologist in Scotland who led the team that created Dolly, has endured growing skepticism about whether his cloning work could be duplicated. He called the latest development "exciting results."
Alan Colman, research director of PPL Therapeutics, the biotechnology firm based in Edinburgh, Scotland, that participated in the cloning of Dolly, called the latest research a "landmark."
Harry Griffin, assistant director of the Roslin Institute, where Wilmut works, said, "We have never had any doubts that Dolly was derived from an adult cell."
To create their families of cloned mice, the Hawaii group used a new technique pioneered by developmental biologist Teruhiko Wakayama from the University of Tokyo, the paper's lead author. The cloned cells were combined mechanically, rather than being fused electrically, as Wilmut's team did with the sheep cells that yielded Dolly.
Yanagimachi admitted somewhat sheepishly that his group only used the mechanical technique because the laboratory could not afford the expensive electro-fusion the Scottish researchers used to clone Dolly.
In addition to Wakayama and Yanagimachi, the Honolulu-based team also included Perry and Maurizo Zuccotti from the University of Pavia in Italy. Kenneth R. Johnson at the Jackson Laboratory in Bar Harbor, Maine, also worked on the experiments.
In all, the Hawaii team conducted a series of four cloning experiments--encompassing more than 1,240 attempts to create genetically identical mice from several different types of mature cells, including brain cells.
With a special micro-pipette, the researchers removed the nucleus of each adult mouse cell and quickly injected it into an egg whose own nucleus had been removed. They then gave the cloned egg cell five to six hours to adjust to its new state before chemically activating it so that the cloned cell would begin to divide and multiply like a normally fertilized embryo.