A synthetic embryo, with a beating heart, an intestinal tract, and the beginnings of a brain was grown using stem cells from mice.

A groundbreaking research project has created the world’s first “synthetic embryos” without sperm, eggs, or fertilization.

Using stem cells from mice, scientists at the Weizmann Institute in Israel created embryolike structures containing an intestinal tract, the beginnings of a brain, and a beating heart.

They are called synthetic embryos because they are created without fertilized eggs, and they could contribute to a deeper understanding of how natural embryos form organs and tissues.

Researchers believe the research will reduce animal experimentation and, eventually, allow for developing new sources of human transplantable cells and tissues. For instance, a leukemia patient’s skin cells could be turned into bone marrow stem cells to treat their illness.

“Remarkably, we show that embryonic stem cells generate whole synthetic embryos, meaning this includes the placenta and yolk sac surrounding the embryo,” revealed Prof Jacob Hanna, who led the effort.

“We are truly excited about this work and its implications.” The work is published in Cell.

Researchers from the same group recently reported being able to grow mouse embryos outside the uterus for several days in a mechanical womb. In the latest study, mice stem cells were nurtured for nearly half their gestation period using the same device.

Pre-treated cells developed into placentas or yolk sacs after treatment with chemicals, whereas untreated cells developed into organs and tissues without treatment.

Only about 0.5% of the stem cells differentiated into distinct tissues and organs, while the majority failed to form embryolike structures. Synthetic mouse embryos had 95% of the same internal structure and genetic profile as natural mouse embryos. It appears that the organs that formed were functional, as far as the scientists could tell.

The synthetic embryos were not “real” embryos as far as development was concerned. They did not have the potential to develop into live animals or had not developed when transplanted into mice’s wombs.

An embryo model of a synthetic mouse is shown in this video on day 8 of development; it has a beating heart, a yolk sac, a placenta, and a developing blood supply.

As per the Guardian, it was crucial to talk about how to regulate the work before human synthetic embryos were created, said Dr. James Briscoe, a principal group leader at the Francis Crick Institute in London.

There is no immediate prospect of synthesizing human embryos, he explained.

Briscoe noted that “we know less about human embryos than we know about mouse embryos, and the inefficiency of mouse synthetic embryos suggests that we will need to develop more before we can translate the findings to humans.”

Professor Paul Tesar, a geneticist at Case Western Reserve University, commented to StatNews that as scientists push stem cell-derived embryos further along the development path, natural and synthetic embryos merge more and more.

He explained that there would always be a gray area. “In order to define what is ethically acceptable, scientists and society should come together to define where the line should be drawn,” the researchers said.

Work like this has been in development for quite some time.

We reported previously that scientists managed to produce an embryo from stem cells while also simulating its implantation into the uterine wall. This was another step in modeling early human development. There was no way for the implanted embryo to develop normally at the time since it was done in a test tube – so instead of using a uterus, they used an organoid called an endometrium.