'Synthetic' mouse embryos created from stem cells

Scientists have created synthetic embryos in mice using stem cells rather than sperm or egg cells. The structures, which were able to implant and grow for a few days in the animals' uteruses, may have important implications for infertility research. 

The team, led by Dr Nicolas Rivron at Maastricht University in the Netherlands, combined two types of mouse stem cells to create structures resembling blastocysts, or early embryos. Instead of traditional gametes, they used embryonic stem cells and trophoblast stem cells, which have the ability to form an embryo and a placenta.

'We pulled them together and discovered a cocktail of molecules that triggered them to self-organise into early embryo cells,' Dr Rivron said.

For the first time, the scientists were able to then implant the resulting blastocyst in the mouse's uterus where they continued to grow for a few days. This breakthrough may pave the way for new research into infertility, especially into the early implantation stages of the development. The study was published in Nature.

Many miscarriages happen when the embryo fails to attach to the womb. However, as most women are unaware of pregnancy at this early stage, the research into the underlying causes is very limited. Greater understanding of the processes involved in successful and unsuccessful implantations may help to understand the causes of infertility and potentially improve the outcomes of treatments. The use of stem cells may also speed up the screening for drugs which help with fertility.

'Because embryos are so precious and scarce, it is almost impossible to test new medicines on them,' said Dr Rivron. 'You would need typically huge numbers of embryos in order to test medicines in the proper way. Here, because we are using stem cells, we can generate an infinite number of early embryos.'

The method has potential applications to human fertility research. However, using it to produce human embryos is still a very remote prospect. According to Dr Rivron, there are currently no plans to extend this line of research to human cells. This would require an ethical approval that is not available in most countries.

Additionally, the blastocyst-like structures produced in this study do not have the ability to develop into further embryonic stages. This is because they contain only two of three cell layers normally present in an embryo, according to Professor Magdalena Zernicka-Goetz at the University of Cambridge, and senior author of an earlier study on embryonic development with stem cells. She believes the next step will be to create 'synthetic blastocysts with greater developmental potential'.