Scientists have created synthetic mouse embryos with developed brains

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The findings, described in a paper in Nature today, could help scientists learn more about how human embryos develop and provide insights into diseases, as well as providing an alternative to animals for testing, according to the researchers.

The new model embryos, which bypass the need for sperm or egg cells, were developed in the lab alongside natural mouse embryos. They mirrored the same stages of development up to eight and a half days after fertilization, developing beating hearts and other foundations of organs, including the neural tubes that eventually turn into the brain and spinal cord.

“I think it’s a major advance,” says Leonardo Beccari from the Center for Molecular Biology Severo Ochoa, in Madrid, who was not involved in the research.

Studying how mouse stem cells interact at this point in development could also provide valuable insight into why human pregnancies fail during the earliest stages, and how to prevent that from happening.

“This is really the first demonstration of the forebrain in any models of embryonic development, and that’s been a holy grail for the field,” says David Glover, research professor of biology and biological engineering at Caltech, a coauthor of the report.

Stem cells are able to develop into specialized cells, including muscle, brain, or blood cells. The synthetic embryos were made of three types of cells from mice: embryonic stem cells, which form the body; trophoblast stem cells, which develop into the placenta; and extraembryonic endoderm stem cells, which help to form the egg sac. 

The embryos were developed in an artificial incubator created by Jacob Hanna of the Weizmann Institute in Israel, who recently kept realistic-looking mouse embryos growing in a mechanical womb for several days until they developed beating hearts, flowing blood, and cranial folds. Hanna is also a coauthor of the new study.

By mimicking the natural processes of how a mouse embryo would form inside a uterus, the researchers were able to guide the cells into interacting with each other, causing them to self-organize into structures that progressed through developmental stages to the point where they had beating hearts and foundations for the entire brain.