They used induced pluripotent skin cells, or iPS cells — cells that have been reprogrammed to look and act like embryonic stem cells. Embryonic stem cells, taken from days-old embryos, have the power to morph into any cell type and, in mice, can be implanted into a mother’s womb to create living mouse pups.

Their experiment, published in Nature, means that it is theoretically possible to clone someone using ordinary connective tissue cells found on the person’s skin, but the experts were quick to distance themselves from such controversy.

“We are confident that tremendous good can come from demonstrating the versatility of reprogrammed cells in mice, and this research will be used to … understand the root causes of disease and lead to viable treatments and cures of human afflictions,” said Fanyi Zeng of the Shanghai Institute of Medical Genetics at Shanghai Jiao Tong University.

“It would not be ethical to attempt to use iPS cells in human reproduction. It is important for science to have ethical boundaries,” she said, adding that their study was “in no way meant as a first step in that direction.”

No one has ever cloned a human being and while many stem cell experiments in mice have been replicated in humans, not all have.

Led by Qi Zhou at the Chinese Academy of Sciences’s State Key Laboratory of Reproductive Biology, the team created iPS cells, using mouse fibroblasts, which are cells found in connective tissue in the skin.

Stem cells are the body’s master cells, giving rise to all the tissues, organs and blood. Embryonic stem cells are considered the most powerful kind of stem cells as they have the potential to give rise to any type of tissue.

But they are difficult to make and require the use of an embryo or cloning technology. Many people also object to using human embryonic stem cells and many countries limit funding for such experiments.

From the skin cells, the Chinese scientists created 37 stem cell lines, and of these, three generated live births.

“One line can generate such competent mice that the longest living one we have is nine months,” Zeng told Reuters.

“It has generated now more than 100 of second-generation (mice) and more than 100 third-generation (mice). It really demonstrates how fertile and strong the system is.”

The Chinese experiment generated questions and caution from other stem cell researchers not connected to the study.

“These investigators have, for the first time, unequivocally demonstrated that the iPS lines they have generated are truly pluripotent,” wrote Andrew Laslett, group leader of Human Embryonic Stem Cell Technology at the Australian Stem Cell Center in Melbourne, Australia.

Pluripotent is a term meaning the cells can give rise to all the tissues in the body.

“Moreover, the long-term stability of both the iPS cell lines and the long-term health of the mice generated using this procedure are yet to be reported. It will be interesting to see whether mice generated in this fashion have a higher propensity for tumor formation,” Laslett wrote.

Following are some facts about stem cells:

* Stem cells are the body’s master cells, the source of all cells and tissue, including brain, blood, heart, bones and muscles.

* Embryonic stem cells come from days-old embryos and can produce any type of cell in the body.

* Scientists generally harvest embryonic stem cells from embryos left over after in vitro fertilization attempts at fertility clinics. They can also be produced using cloning technology but the new U.S. rules allow for federal funding only of work on surplus IVF embryos.

* Scientists hope to harness the transformational qualities of stem cells to treat a variety of diseases, including injuries, cancer and cystic fibrosis.

* The issue is controversial because some people believe the destruction of any human embryo is wrong.

* Several companies are pursuing stem cell research including Geron Corp. which last week teamed up with General Electric Co to use stem cells to test new drugs for toxicity.

* Other companies involved in stem cell research include Stemcells Inc., Advanced Cell Technology, NeuralStem, Aastrom Biosciences Inc., Reneuron Group Plc., Thermogenesis, Osiris Therapeutics Inc, Neostem Inc., Cytori Therapeutics Inc., iZumi Bio Inc., and International Stem Cell Corporation.

*U.S. legislation called the Dickey Amendment forbids the use of federal funds for the creation or destruction of human embryos for research, but new U.S. policy allows federally funded researchers to work with cells someone else had taken from an embryo.

* The issue does not fall clearly along party lines and some conservative Republicans who oppose abortion have backed broader federal funding of embryonic stem cell research for years.

* Britain, Belgium, Sweden, Canada and New Zealand encourage embryonic stem cell research. Austria, Lithuania and Poland have laws banning most human embryonic stem cell research.

* Researchers have discovered how to make embryonic-like cells from ordinary cells, called induced pluripotent stem cells. Opponents of embryonic stem cell research say research can focus on this field, but most scientists agree that all approaches must be pursued.

Hwang, once a scientist with rock-star like status in South Korea for his research that brought the country to the forefront of stem cell studies, is facing trial on charges of fraud, misusing 2.8 billion won ($2.25 million) in state funds and violating bioethics laws.

Prosecutors said Hwang brought shame to the country and harm to scientific research in South Korea.

“The disappointment felt by the (Korean) people is enormous,” one of the team of prosecutors told the court.

Hwang, who has apologized for fraud in his team’s work, has denied any wrongdoing and said he was duped by junior researchers into believing the landmark results

Lee Bong-gu, a lawyer for Hwang, said: “These people, including the prosecutors are trying to tear apart Hwang’s precious scientific evidence.”

Hwang’s trial at a nondescript Seoul court has been going on for about three years, and could stretch into a fourth, legal experts said. It has been bogged down in the technical testimony from scores of scientists about the research done by his team.

His supporters have staged emotional rallies over the years and filled the court for each of what are typically monthly hearings, saying Hwang is a scientific savior who should be given a second chance.

Hwang’s team was thought to have made two major breakthroughs in the field by cloning stem cells and tailoring them to a specific patient, which raised hopes of generating genetically specific tissue to repair damaged organs or treat diseases such as Alzheimer’s.

Stem cells are the body’s master cells, giving rise to all the tissues, organs and blood. Embryonic stem cells are considered the most powerful kinds of stem cells, as they have the potential to give rise to any type of tissue.

An investigation team at Seoul National University, where Hwang once worked, said in late 2005 that Hwang’s team deliberately fabricated vital data in the two papers on human embryonic stem cells.

It did verify, however, that Hwang’s team produced the world’s first cloned dog, an Afghan hound named Snuppy.

“Hwang’s fall discouraged the government from supporting stem cell studies. It also meant that researchers in the field were the objects of scorn,” said Oh Il-hwan, a Catholic University Medical school professor specializing in bioethics.

With major financial backing from his supporters, Hwang went on to form Sooam Biotech Research Foundation in 2006, which specializes in animal cloning and has produced cloned dogs.