A research team in the UK and the US has created “synthetic” mouse embryos that developed a brain, nerve cord and beating heart tissue in the lab without the need for a fertilized egg or uterus to grow.
It is similar to a breakthrough by an Israeli team, published earlier this month. Together, the advances promise to revolutionize understanding of one of biology’s greatest challenges: how a few cells organize themselves into life.
If applied to human embryos, the research could help understand human fertility, developmental disorders and provide a new avenue for developing lab-grown tissues or organs for transplant.
But applying the technique to human embryos would increase important ethical and legal issues.
“The big question we’re addressing in the lab is how do we start our lives?” says Professor Magdalena Zernicka-Goetz of Caltech in Pasadena, California, and the University of Cambridge in the UK.
To create synthetic embryos, or “embryoids,” scientists took three types of stem cells from a mouse embryo that would normally form all the tissues needed in a growing embryo.
They then transferred the cells to an artificial growth medium, essentially a rotating flask of nutrients.
The stem cells spontaneously formed embryos.
Only about one in 100 was successful, but the few that were “are absolutely indistinguishable in many cases from natural embryos,” says Professor Zernicka-Goetz.
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The embryos only developed for eight and a half days, about half the normal gestation period for a mouse.
But the technique should still be very important as a way to produce early embryos with which to study early development, without the need for experimental animals.
The team is currently actively working on a human embryo model, but the focus is far away. There are significant differences between early mice and early human development.
But having a synthetic human embryo could be a major breakthrough for the study of fertility and common developmental disorders.
“Most human pregnancies are lost in the early stages of our lives,” says Professor Zernicka-Goetz, “and IVF fails in 20-70% of cases.”
Supplies of donated human embryos are scarce and often of poor quality, so a lab-grown “model” embryo could help answer many questions.
The team proposes synthetic embryoids that reproduce only one element of an early human embryo, such as the heart, or the tissue that forms the placenta during implantation. Implantation failure is one of the main causes of IVF pregnancy failure.
Synthetic human embryos could also be a way to generate new tissues or organs for “regenerative” medicine. If derived from a patient’s stem cells, these tissues could be a perfect match for the recipient.
However, the development of synthetic human embryos would require, at least in the UK, a change in the current law that does not cover the growth of embryos from stem cells.
UK law also prevents human embryos from being grown in the laboratory past 14 days. This is before most of the important developmental processes observed in these mouse embryos occur.
This latest demonstration means that discussion of these legal and ethical issues should begin sooner rather than later, experts say.
“The result does announce that, in the future, similar experiments will be done with human cells and that, at some point, they will give similar results,” says Professor Alfonso Martínez Arias of the Pompeu Fabra University in Barcelona, who does not it was related to the investigation. .
“This should encourage considerations about the ethics and social impact of such experiments before they occur,” he added.
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