The experiment was carried out using mice and produced seven babies, six of which lived to adulthood. The breakthrough may help scientists to understand more about how animals produce sperm. This knowledge has potential applications in the treatment of male infertility.

Karim Nayernia, who has just taken up a post as Professor of Stem Cell Biology at Newcastle University, led the research while in his previous position at Georg-August University in Göttingen, Germany, with Prof. Dr Wolfgang Engel and colleagues from Germany and the UK, including Dr. David Elliott from Newcastle University's Institute of Human Genetics.

Nayernia and his team describe in their paper how they developed a new strategy for generating mature sperm cells in the laboratory using embryonic stem cells from mice. They then went on to test whether this sperm would function in real life.

The team isolated stem cells from a blastocyst, an early-stage embryo that is a cluster of cells only a few days old. These cells were grown in the laboratory and screened using a special sorting machine. Some had grown into a type of stem cell known as 'spermatogonial stem cells', or early-stage sperm cells.

The spermatogonial cells were singled out, then genetically marked and grown in the laboratory. Some of them grew into cells resembling sperm, known as gametes, which were themselves singled out and highlighted using a genetic marker.

The sperm that had been derived from the embryonic stem cells was then injected into the female mouse eggs and grown into early-stage embryos. The early-stage embryos were successfully transplanted into the female mice which produced seven babies. Six developed into adult mice.

Nayernia said: "This research is particularly important in helping us to understand more about spermatogenesis, the biological process in which sperm is produced. We must know this if we are to get to the root of infertility.; Source: University of Newcastle upon Tyne