Eggs capable of being fertilised and making babies can be created in the laboratory from skin cells, a study has shown.

Scientists successfully produced three fertile baby mice using the technique, which involves transforming ordinary skin cells into personalised stem cells.

The same Japanese team created viable mouse sperm from embryonic stem cells earlier this year.

Together, both advances greatly increase the likelihood of radical and controversial future treatments for restoring fertility. It could mean creating sperm for men whose fertility has been wiped out by cancer therapy or reversing the menopause in women long after they have used up their natural supply of eggs.

In August, scientists from Kyoto University in Japan announced that they had created sperm cells from mouse embryo stem cells. Injected into mouse eggs, the sperm produced embryos which developed into healthy baby mice.

The same team, led by Dr Katsuhiko Hayashi, carried out the latest research which focused on eggs rather than sperm. The scientists mirrored their earlier achievement by transforming stem cells from mouse embryos into eggs which could be fertilised to produce offspring. But they also took a further step by obtaining mouse pups from eggs derived from ordinary skin cells.

The researchers wrote in the latest online issue of the journal Science: "Our system serves as a robust foundation to investigate and further reconstitute female germline development in vitro (in the laboratory), not only in mice but also in other mammals, including humans."

The "germline" consists of genetic material carried in reproductive cells that can be passed onto future generations.

Dr Allan Pacey, senior lecturer in reproduction and developmental medicine at the University of Sheffield, said: "This is a very technical piece of work which pushes much further the science of how eggs are generated and how we might one day be able to routinely stimulate the new production of eggs for women who are infertile.

"What is remarkable about this work is the fact that, although the process is still quite inefficient, the offspring appeared healthy and were themselves fertile as adults. This is a great step forward but I would urge caution as this is a laboratory study and we are still quite a long way from clinical trials taking place in humans."

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Eggs can be created from skin cells