British scientists say they have taken a step towards showing human eggs and sperm can be created from stem cells.
The finding may help IVF treatment, hit by a shortage of egg and sperm donors.
Previous research had found mice stem cells were capable of developing into sperms and eggs so the researchers checked if this was true in humans.
The Sheffield University team found some stem cells developed the genetic signature of primordial germ cells, the ancestors of eggs and sperm.
The work may make up for a shortage of egg and sperm donors for IVF treatment.
This lack of egg and sperm donors has led to the growing trend of fertility tourism - couples seeking help abroad.
The team from Sheffield University say many more tests are needed to check the technique is safe.
Typically, sperm banks have relied on donations from younger men in their 20s, targeted through football programmes, magazines and student unions.
Egg donation is more intrusive and riskier, making it more difficult to recruit donors.
But numbers of both donors have been dwindling.
Some say that laws lifting anonymity on donations from April 1 this year might put off even more potential donors.
Other research looked at stem cells from mice and found they could be encouraged to change into early sperm and egg cells, called primordial germ cells (PGCs), and eventually mature sperm and eggs.
The team at the Centre for Stem Cell Biology in Sheffield decided to see if the same was true in humans.
Sperm production
Using stem cells taken from embryos donated for research by couples undergoing IVF, they found some formed into a collection of cells called embryoid bodies.
When they looked at these cells in detail they found that within two weeks a small number of cells expressing some of the genes found in human primordial germ cells were present.
Some cells also expressed proteins only found in maturing sperm.
Mr Behrouz Alfatoonian, one of the team which carried out the study, said: "This suggests that human stem cells may have the ability to develop into primordial germ cells and early gametes as has been shown previously for mouse embryonic stem cells."
He said the challenge now was to choose the cells that were going to develop into primordial germ cells and then work out how to encourage them to grow into mature sperm and egg.
"Producing functional gametes is much more difficult because we have to recreate for the cultured cells the environment of the developing follicle for the egg or the tissue of the testis for the sperm."
Professor Harry Moore, who runs the centre, said: "Ultimately, it might be possible to produce sperm and eggs for use in assisted conception treatments."
British Fertility Society secretary Dr Allan Pacey said: "This is a really exciting step forward that has huge implications for the way we could undertake research studies to investigate the processes of egg and sperm development.
"We still don't really understand why some men and women can't produce sperm and eggs of their own, and sadly for them that leads to infertility. But if we could better understand the basic biology then we might be in a better position to help them one day."
Laura Witjens of the National Gamete Donation Trust said: "Donation has gone down over the last eight or nine years. Any research that could ultimately help patients requiring egg or sperm is fantastic news."
Stem cell finding offers IVF hope
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Originally Posted by Louis VI the Fat
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