Sperm created from embryonic stem cells can give rise to live offspringCredit: Karim Nayernia

For the first time, embryologists have shown that sperm created from embryonic stem cells can give rise to live offspring. The work, carried out by researchers in Germany and Britain, culminated in the production of six adult mice that owed their origins to sperm derived from these 'multipurpose' cells.

But the technique certainly isn't perfect: the success rate was very low, and the mice suffered genetic abnormalities. So there is no immediate prospect of the method being adapted to treat infertile men. But the discovery could lend valuable insights into the process by which functioning sperm are manufactured.

Ordinarily, sperm cells develop from precursors known as 'spermatogonial stem cells' (SSCs) in the testes. In the new research, a team led by Karim Nayernia at the University of Göttingen, Germany succeeded in converting stem cells taken from early mouse embryos into SSCs, and from there into functioning sperm.

Both sperm cells and eggs have been made from stem cells before. But this research goes further.

The researchers implanted the sperm artificially into eggs collected from mice, and showed that the sperm were capable of fertilizing the eggs, which produced living offspring when implanted into surrogate mothers. "We have shown that the sperm cells are functional, and can fertilize an oocyte," says Nayernia.

Dying young

Of 210 eggs injected with the lab-reared sperm, only 65 began to undergo cell division, and only seven live births resulted, with one of these offspring failing to reach adulthood, the researchers report in the journal Developmental Cell¹.

The other six mice were all smaller or larger than control mice thanks to abnormal growth rates. All died within 5 months of their birth; mice usually live for years. The problems are probably introduced, the researchers say, during imprinting: a change in the pattern of genes that are switched on, or expressed, in the embryo.

Learning how sperm are produced could ultimately help in treating infertile men in whom this pathway is defective, suggests John Burn, head of the Institute of Human Genetics at the University of Newcastle upon Tyne, where Nayernia now works. "From a scientific point of view, this should be seen as a milestone in understanding how cells produce functioning sperm."

The technique could also be honed to remove the need to use stem cells taken from embryos, Burn suggests. One possibility, he says, is to use stem cells from blood in the placenta or umbilical cord, which is rich in these highly adaptable proliferating cells.

Any human application is nevertheless a long way away, other researchers warn. "It is more difficult to say whether artificial sperm produced this way could ultimately be used as a new treatment for male infertility," says Allan Pacey, who studies male reproductive problems at the University of Sheffield, UK. "There are many technical, ethical and safety issues to be confronted before this could even be considered."

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University of Newcastle upon Tyne

• References

  1. Nayernia K., et al. Dev. Cell, 11. 1 - 8 (2006). | PubMed |