Scientists at Cambridge University have grown a living mouse embryo in a lab, from stem cells. The cells developed outside of the body, inside a blob of gel. They were allowed to develop for seven days, which is about one third of the way through a mouse pregnancy. By that point, the embryo contained all of the internal structures that develop during growth in the womb, with cells organizing into two sections that later develop into the placenta and the embryonic mouse.

University of Cambridge developmental biologist Magdalena Zernicka-Goetz, who led the research, said:

“I’m looking at it as a miracle of nature as well as trying to understand the process. It’s incredibly beautiful that we can begin to understand those forces that give rise to self-organisation during the earliest stage of development.”

The researchers were not seeking to create full-grown mice, but instead were investigating the developmental process of the embryo. Prior to this breakthrough, scientists have been unable to recreate the three-dimensional structure of the embryo outside the body, and when in the mother’s womb, the structures are too small to observe in detail using ultrasound.

According to Zernicka-Goetz, “This is the time of implantation when the embryo is invading the body of the mother. Weeks later you can observe it with ultrasound but at this stage it is very mysterious. It’s a developmental black box.”

Scientists have said that up to two thirds of miscarriages occur bure the embryo has been implanted, sometimes before women are even aware they are pregnant. “To really understand the key principles of pregnancy at this stage would be very helpful,” Zernicka-Goetz added.

The researchers used embryonic stem cells, which are able to develop into any cell type in the body, instead of working with a fertilized egg. This approach could also allow for further research on human embryos, with a virtually endless supply of embryonic stem cells available.

“We are very optimistic that this will allow us to study key events of this critical stage of human development without actually having to work on embryos. Knowing how development normally occurs will allow us to understand why it so often goes wrong,” according to Zernicka-Goetz.

Despite a close resemblance to a real embryo, researchers were skeptical that it would have developed into a healthy fetus. To do so, it would require a yolk sac, which supplies nourishment for the embryo and allows a network of blood vessels to develop.

The next step for researchers will be to use the same process to create artificial human embryos, to help understand what can go wrong during early pregnancies.

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