Using only skin cells, the Israeli laboratory creates artificial mouse embryos with beating hearts

An Israeli laboratory has grown artificial mouse embryos with beating brains and hearts – in an egg-free, sperm-free procedure that uses stem cells taken from the skin.

The breakthrough, published Monday in the peer-reviewed journal Cell, marks the first time an advanced embryo has been created from any type of stem cell alone, cell biologist Professor Jacob Hanna of the Weizmann Institute of Science told The Times of Israel.

Hanna, whose team of researchers includes Israeli Jews and Arabs as well as a Palestinian doctoral student, said previous attempts had only resulted in blastocysts, that is, structures formed in early mammal development. The blastocyst contains a tiny fraction of the more than 1 million cells in its embryos.

“It’s amazing,” he commented. “There were no sperm, no egg, no uterus, but we were able to create embryos from stem cells alone up to eight days – a third of a mouse’s pregnancy – with a beating heart.”

He said the research could one day be used to grow human embryo-like structures to generate cells for future medical solutions.

Scientists are constantly working on ways to use cells to grow organs for transplant. The obvious source of such cells – normal embryos – is seen as riddled with ethical problems.


An image of an artificial mouse fetus that was grown at the Weizmann Institute of Science, from day one at the top left, to stay at eight at the bottom right. (Courtesy of the Weizmann Institute of Science)

Hanna said the artificial, embryo-like structures could be viewed very differently. They are similar to normal embryos, but not implantable.

He anticipates a day when patients can donate skin or blood cells for the growth of artificial embryo-like structures, which in turn can produce the cells needed for organ growth.


An artificial mouse embryo grows at the Weizmann Institute of Science on day 8, complete with a beating heart. (Provided by the Weizmann Institute of Science)

The key to Hanna’s achievement is a special incubator system in which each embryo is in a bottle with liquid, and the bottle is rotated to ensure it doesn’t stick to the side. The incubator creates all the conditions necessary for the development of the fetus, including gas concentration, pressure and temperature. Developed in his lab, the liquid gives fetuses all the nutrients, hormones and sugars they need.


Dr.. Jacob Hanna in his lab at the Weizmann Institute. (Courtesy of Jacob Hanna)

In March 2021, Hanna’s lab used the incubator to grow 250-cell embryos into mouse embryos with fully formed organs using artificial wombs. “The difference between this research and what we have achieved now is where the embryos come from,” Hanna explained. “In the previous study, they were normal embryos that came from mice and grew up as eggs fertilized with sperm. Now, the embryos are made only from stem cells.”

He added, “We were asking at the time of the previous study what would happen if we just took stem cells and put them into this organ. Now we know the answer – embryos with early organs, including early brain, beating heart, and blood stem cells. They even mimic the entire fetus. The tissues surrounding it include the placenta and the yolk sac.

“No one has ever made advanced embryos from stem cells, so this is important. This will advance the understanding of stem cells and organs in mammals, and is likely to be of practical importance in the future.”

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