Researchers created the world’s first “synthetic embryos” in a groundbreaking feat that avoided the need for sperm, eggs and fertilization.
Scientists at the Weizmann Institute in Israel have found that mouse stem cells can self-assemble into embryo-like structures with an intestinal tract, the beginning of a brain and a beating heart.
Known as synthetic embryos because they are created without fertilized eggs, the living structures are expected, in the short term, to lead to a deeper understanding of how organs and tissues form during the development of natural embryos.
But the researchers believe the work could also reduce animal experimentation and ultimately pave the way for new sources of cells and tissues for human transplantation. For example, skin cells from a leukemia patient could potentially be turned into bone marrow stem cells to treat her condition.
“Notably, we showed that embryonic stem cells generate whole synthetic embryos, which means that this includes the placenta and yolk sac around the embryo,” said Professor Jacob Hanna, who led the effort. “We are really excited about this work and its implications.” The work is published in Cell.
Last year, the same team described how they built a mechanical uterus that allowed natural mouse embryos to grow outside the uterus for several days. In the most recent work, the same device was used to nourish mouse stem cells for more than a week, nearly half the gestation time of a mouse.
Some of the cells were pre-treated with chemicals, which activated genetic programs to develop into the placenta or yolk sac, while others developed without intervention in organs and other tissues.
While most stem cells failed to form embryo-like structures, about 0.5% combined into tiny balls that developed distinct tissues and organs. When compared to natural mouse embryos, the synthetic embryos were 95% the same in terms of the internal structure and genetic profiles of the cells. As far as scientists could tell, the organs that formed were functional.
Hanna said the synthetic embryos were not “real” embryos and had no potential to develop into live animals, or at least not when they were transplanted into the wombs of mice. He founded a company called Renewal Bio that aims to grow synthetic human embryos to supply tissues and cells for medical conditions.
“In Israel and many other countries like the US and UK it is legal and we have ethical approval to do this with human-induced pluripotent stem cells. This is providing an ethical and technical alternative to using embryos,” Hanna said.
James Briscoe, one of the group’s main leaders at the Francis Crick Institute in London, who was not involved in the research, said it was important to discuss how best to regulate the work before synthetic human embryos were developed.
“Synthetic human embryos are not an immediate prospect. We know less about human embryos than mouse embryos, and the inefficiency of synthetic mouse embryos suggests that translating the findings to humans requires further development,” Briscoe said.
But, he added: “Now is a good time to consider the best legal and ethical framework to regulate research and use of human synthetic embryos and update current regulations.”
Speaking to StatNews, Professor Paul Tesar, a geneticist at Case Western Reserve University, said that the further scientists push stem cell-derived embryos further and further down the developmental path, the more the synthetic and natural embryos begin to fuse.
“There will always be a gray area,” he said. “But as scientists and as a society, we need to come together to decide where the line is and define what is ethically acceptable.”