WASHINGTON Researchers have taken ordinary skin cells from a mouse and reprogrammed them to look and act like embryonic stem cells in a long-promised experiment that provides an alternative way to get the valued and controversial cells.
Three studies published on Wednesday show various ways to turn the clock back and make an ordinary cell act like an embryonic stem cell -- the ultimate master cells of the body.
A fourth showed a way to use discarded, abnormal embryos from fertility clinics to make embryonic stem cells.
All of the researchers worked in mice and say it will be a while before they can demonstrate their techniques using human cells.
Embryonic stem cells are the source of every cell, tissue and organ in the body. Scientists study them to understand the biology not only of disease, but of life itself, and want to use them to transform medicine.
But their use is controversial, with opponents saying it is wrong to use a human embryo in this way. U.S. President George W. Bush has blocked legislation that would expand federal funding of such research.
The U.S. House of Representatives was expected to give final congressional approval on Thursday to another bill promoting the research -- but Bush has promised to veto it.
The researchers said they were not trying to get around the politics of the issue.
"The reason that we embarked on these experiments was not to come up with a solution to those people who have objections to embryonic stem cell," Dr. Kevin Eggan of the Harvard Stem Cell Institute, who led one of the studies, told reporters.
"All of us strongly agree with human embryonic stem cell research. These experiments were not motivated by a desire to find an end run around those issues."
In one of the studies, Dr. Rudolf Jaenisch of the Whitehead Institute in Cambridge, Massachusetts and colleagues turned mouse skin cells into embryonic stem cells.
They identified four proteins, called factors, that are active only in mouse embryonic stem cells and not in adult cells. "You introduce those four factors, which induce or kick these cells into a process which we call the reprogramming process," Jaenisch said in a telephone interview.
The ordinary skin cells, which normally would only make skin and which would die in the lab after a while, instead proliferated in lab dishes.
And when injected into other mouse embryos, they created chimeras -- animals with the genetic characteristics of two different individuals.
This opens the possibility of using stem cells to treat genetic disease.
Shinya Yamanaka of Kyoto University and colleagues, who first invented this technique, reported similar findings in a second paper.
In a separate report, Eggan and colleagues tried a different way to clone an adult cell, using a fertilized egg instead of an unfertilized one.
The cloning method called somatic cell nuclear transfer, used to make Dolly the sheep, involves removing the nucleus from an unfertilized egg, and replacing it with the nucleus of an adult cell.
Eggan's team used abnormal embryos from fertility clinics. Some fertilized embryos at in vitro fertilization or IVF clinics contain two or more sperm.
"They cannot develop into a normal embryo," Eggan said. They have too many chromosomes, and would die.
Eggan's team removed this genetic material and replaced with the DNA of an adult cell. This worked just like somatic cell nuclear transfer to get the egg dividing.
Eggan calculated that tens of thousands of such abnormal embryos are created, and discarded, each year.
He said both methods are being tried now using skin samples from patients who have amyotrophic lateral sclerosis, also known as ALS or Lou Gehrig's disease, a fatal and incurable paralyzing condition.