Scientists have created mouse eggs from stem cells and used them to make healthy baby mice. The technique will help them study how eggs develop and also offers the potential to create eggs for infertile women.
Mitinori Saitou of Kyoto University led a team that took stem cells from mice and genetically reprogrammed them to become egg precursor cells. When these were mixed with appropriate body cells from female mice to make "reconstituted ovaries" and implanted into mice, they developed into mature eggs. These were then successfully fertilised in the lab by IVF and the resulting mouse pups were healthy and fertile.
The results are described on Thursday in the journal Science. Scientists at the University of Pennsylvania transformed mouse stem cells into eggs in 2003, but did not use them to create mouse pups.
"Our system serves as a robust foundation to investigate and further reconstitute female germline development in vitro, not only in mice, but also in other mammals, including humans," wrote the authors in Science.
Saitou used two types of stem cells in his work: embryonic stem cells, which are found in early-stage embryos and can turn into any type of tissue in the body; and induced pluripotent stem cells, which are made by taking a cell from an adult (such as a skin cell) and reprogramming it into a state similar to an embryonic stem cell.
The proportion that went on to create healthy offspring was relatively low — five pups were born from 127 implanted embryos (3.9%) in the case of stem cells compared with 13 pups out of 75 embryos (17.3%) in one of the controls, which started with normal mouse reproductive cells.
Saitou's latest research extends his work from last year, when he led a team of scientists that created viable sperm from mouse stem cells and used them to create healthy, fertile offspring through IVF.
Dr Allan Pacey, a fertility expert at the University of Sheffield and chair of the British Fertility Society, 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 are 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."
In the shorter term, being able to create eggs in the lab from stem cells could help scientists to better understand female infertility by giving them insights into how eggs age and how they sometimes develop incorrectly.
Robert Norman, a professor of reproductive and periconceptual medicine at the University of Adelaide, said the research would one day allow infertile women to have genetically related children, but that would be far in the future. "Major concerns still need to be addressed including long-term health of the offspring," he said.
