Using three kinds of mouse stem cells, biologists at the University of Cambridge have created living embryos with beating hearts, all parts of a developing brain, and the beginnings of all other organs in a mouse’s body.

Two kinds of the stem cells support an embryo’s growth and development; the other kind becomes the various organs and tissues of the body.

The researchers cultivated each of three types of cells separately, then combined them when all three reached the point at which they were ready to interact and self-organize.

The embryos continued developing normally for about 8.5 days, which is roughly halfway through a normal mouse pregnancy.

TRENDPOST: Many human pregnancies fail when different kinds of rudimentary cells begin to communicate but can’t work together. Being able to replicate and observe what has been a mysterious phase of fetal development in mice could give clues to why such pregnancies self-destruct.

More broadly, scientists now can link specific genes to the development of specific parts of a fetus. Many genes—in the brain, for example—are present but their purpose isn’t known.  By knocking them out, researchers can see what the effect is.

It will trouble some people that the researchers are planning similar studies using synthesized human embryos. British law, which governs the Cambridge scientists, allows experimentation on human fetuses up to the age of 14 weeks.

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