A team of U.S. and French biologists has stunned the scientific world by creating a mouse egg from a mouse embryo cell, and then going on to create a mouse embryo from the egg, bypassing normal fertilization. The result has far-reaching implications for the current debate over stem cells and cloning.
The embryo cell that gave rise to the mouse egg was a stem cell. Stem cells can develop into all other cell types, allowing a fetus to grow into a fully formed mammal with different organs.
Scientists have been able to coax stem cells into developing into many types of mammal cells in the laborator, like muscle, but until now they have not been able to do this with reproductive cells. They thought that this could be done only within the body, because of special physical conditions that could not be duplicated in the lab.
Now, researchers have shown differently in a study published in the journal Science. "Actually, what we saw is that it is so easy that people would be very surprised how easy it is," said Hans Scholer.
University of Pennsylvania microbiologist Hans Scholer and his U.S. and French colleagues say, not only have mouse stem cells become egg cells, but also the cells spontaneously developed into early stage mouse embryos. "We are doing this from the very beginning, until the very end of egg formation," he said. "We have a process in the dish, which is very similar to the process of ovulation in the organism."
In a laboratory dish culture, the mouse embryo stem cells first gathered into colonies of various sizes. Within two weeks, individual cells broke away and recruited other cells to nurture them. After two more weeks, egg cells developed in the culture. Mr. Scholer says that less an three weeks after that, embyro-like structures arose spontaneously without fertilization by sperm. "When we saw this the first time, we were very surprised. We first didn't think we could carry it on so far," he said.
Mr. Scholer says the spontaneous embryos could not be used to reproduce mice, because they contain an incomplete set of genetic material.
If this technique can be duplicated with human tissue, if it can produce embryo-like structures that are not true human embryos, the Pennsylvania scientists believe it could provide an artificial means of providing embryo stem cells. Such cells are considered the best hope for providing new tissue to treat many disorders, where old tissue does not function properly. They say their method would overcome the fears of stem cell research opponents, who do not want human embryos aborted as a source of the cells.
Bioethicist Thomas Murray of the Hastings Center in New York State suggests one area where the new technique might help. "If it is extended to humans, there will be some therapeutic applications that we will celebrate," he said. "For example, women who cannot make healthy eggs right now, perhaps could benefit by this process."
Mr. Murray says the research will cause rethinking of the ethics of stem cell research.
But for some opponents of such research, no rethinking is necessary. Daniel McConchie of the Center for Bioethics and Dignity in Chicago says that any human embryo is a life that should not be destroyed, whether it can develop into a fully formed person or not. "We've never asserted that certain members of the human species, just because they can't survive a particular period of time, don't then deserve the rights of other human beings," he said. "In a sense, we're all terminal, and we don't take away the rights of someone just because he is on his deathbed."
It is too early to know how the new study might affect the politics of stem cell research. Many nations have imposed limits on it. In the United States, President Bush has prohibited government funding for such research, if the cells were derived after his edict. Congress is working on a measure to outlaw cloning human embryos as a source for stem cells.
