Scientists may have found what they hope is a less controversial way of getting special human cells that can turn into any part of the body and potentially solve many diseases. Scientists already know they can get these cells from human embryos—but many people oppose this and the federal government has banned most research. But as this ScienCentral News video reports, this new source doesn't use embryos.
Stem cell research is leading scientists to investigate the possibility of regenerative or reparative medicine—treatments in which stem cells "turn into" a specific cell type required to repair damaged adult cells.
It's a controversial topic because one source of stem cells is the destruction of embryos. But genetics researchers say they found a new source for stem cells—unfertilized egg cells created by a process called parthenogenesis, a form of reproduction in which the egg develops without being fertilized.
"Parthenogenesis is derived from the Greek terms 'parthenos' and 'genesis'," explains Kent Vrana, professor of physiology/pharmacology at Wake Forest University Baptist Medical Center. "Parthenos is virgin, and genesis is birth. So parthenogenesis is the process whereby an organism develops from an activated egg without the benefit of sperm. In lower organisms, like reptiles, fish, and insects, this is a fairly common mode of reproduction; the egg activates without sperm. For instance, the male drone honeybee is the product of parthenogenesis."
Vrana and his team, collaborating with scientists at Advanced Cell Technology, used egg cells from monkeys and stimulated them to begin dividing without being fertilized. "We can take the egg [and] activate it into thinking it's been fertilized without using sperm," says Vrana. "It begins development but it ceases at a point where normally it would implant into the uterus...even though it will develop into a ball of cells, it will not implant." That's because in mammals, sperm is necessary for placenta formation, Vrana explains. "Without that, you don't have a viable embryo."
|Egg cells can be activated to start dividing without being fertilized by sperm.|
image: Wake Forest University School of Medicine
"The advantage is that at that point that it has developed to, we can derive stem cells from it," says Vrana. The resulting stem cells have produced muscle cells, nerve cells, and heart cells. "The hope is that we can take those cells, figure out how to trick them into becoming various cells we need for therapy, and then using them to cure human diseases," he says.
Vrana says that assuming it will also work with human egg cells, this new method is an alternative to using viable human embryos. "We've tested these cells by every known criterion for embryonic stem cells, and we find that they are identical to human embryonic stem cells in their behavior," says Vrana. "What this says, then, is that we can create stem cells that look like embryonic stem cells but do not require the destruction of fertilized embryos. What we are talking about here is an activated egg, not a new genetic entity, not a potential fetus or baby, but rather an activated cell. Although it develops like an embryo, it is nonviable—if placed back in the womb, this activated egg will not become a fetus."
While some may agree this is an ethical alternative, the federal ban on the use of embryos right now also explicitly includes parthenogenesis. However, Vrana hopes that everyone involved might find this new method both useful and acceptable. "I would like to think that our findings in the monkey will be translated into the human. But what we'll have to do, is wait until the President releases federal funds to do these experiments in humans, which they can't be right now."
Vrana emphasizes that parthenogenesis may be "one ethical alternative," in part because it can only be used to make therapeutic cells for women, who produce egg cells. Until they figure out a way to activate sperm to divide, men would be out of luck.
This research appeared in the September 2003 issue of Proceedings of the National Academy of Sciences, and at the National Academy of Sciences Colloquium, "Regenerative Medicine." It was funded by Advanced Cell Technology and the National Institute on Alcohol Abuse and Alcoholism.