Offering a new ray of hope to infertile couples, researchers have now coaxed stem cells, from a mouse embryo, to produce both eggs and sperm in the same dish.
This method brings researchers closer to their ultimate aim: producing human eggs and sperm from adult body cells so that infertile men and women can have their own children.
Applying the technique to humans would be controversial, not least because it raises the possibility that men might be able to produce eggs, and women sperm. But researchers point out that any human application would be decades away, which would allow time for ethical debate over the technology.
In the meantime, they hope that lab-produced eggs and sperm will help them to learn exactly how these cells are created in the body, something that is crucial to understanding fertility disorders and embryo development.
The achievement builds on previous work using mouse embryonic stem cells to grow eggs and sperm. In 2003, Hans Sch?ler of the University of Pennsylvania in Philadelphia and his colleagues reported that after such cells had been cultured for around 40 days, some of them spontaneously produced eggs1.
The following year, researchers led by George Daley of the Whitehead Institute for Biomedical Research in Cambridge, Massachusetts, coaxed cells into producing sperm precursors, by adding a chemical messenger called retinoic acid2. These cells did not form mature sperm, but were able to fertilize eggs when injected into them.
Alan Trounson, a stem-cell researcher at Monash University in Melbourne, Australia, is impressed by the eggs and sperm produced. “I haven’t seen sperm of that maturity produced in the lab,” he says.
He cautions that the work is at an early stage, and points out that for such work to be of therapeutic use in humans, researchers will require much better control over the process. “It will need to be much more directed,” he says.
The idea is that eventually, infertile men or women could clone a body cell to produce an embryo, from which embryonic stem cells would then be extracted. These could then be coaxed into producing viable eggs or sperm. That would be “a big loop”, admits Trounson, but he says it could be possible within 20 or 30 years.
In the meantime, eggs produced in the lab would be of use for research, for example to produce embryonic stem-cell lines. Harvesting eggs from women is a painful and risky process, so the supply of eggs is a major limiting factor. “Everyone’s looking to see if we’ll be able to get some more eggs from somewhere,” says Kerkis.