Researchers have created the world’s first “synthetic embryos” in a ground-breaking feat that bypassed the need for sperm, eggs and fertilization.
Scientists at Israel’s Weizmann Institute found that mouse stem cells could be made to self-assemble into early embryo-like structures with an intestinal tract, the beginnings 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 further 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 to new sources of cells and tissues for human transplantation. For example, skin cells from a leukemia patient could potentially be transformed into bone marrow stem cells to treat their condition.
“Remarkably, we show that embryonic stem cells generate whole synthetic embryos, meaning this includes the placenta and yolk sac that surround 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 had built a mechanical womb that allowed natural mouse embryos to grow outside the uterus for several days. In the latest work, the same device was used to nurture mouse stem cells for more than a week, almost half the gestation time of a mouse.
Some of the cells were pre-treated with chemicals, which activated genetic programs to become placenta or yolk sac, while others developed without intervention into organs and other tissues.
Although most of the stem cells failed to form embryo-like structures, about 0.5% combined into small balls that grew different tissues and organs. Compared to natural mouse embryos, the synthetic embryos were 95% identical in terms of their internal structure and the genetic profiles of the cells. As far as the scientists could tell, the organs that formed were functional.
Hanna said the synthetic embryos were not “real” embryos and did not have the potential to become living animals, or at least not when they had been transplanted into the wombs of female mice. He has founded a company called Renewal Bio that aims to grow synthetic human embryos to provide tissues and cells for medical conditions.
“In Israel and many other countries, such as the US and UK, it is legal and we have ethical approval to do this with human induced pluripotent stem cells. This provides an ethical and technical alternative to the use of ’embryos,’ Hanna said.
Dr James Briscoe, leader of the main group 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 human synthetic embryos are 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 the research and use of human synthetic embryos and to update existing regulations.”
Speaking to StatNews, Professor Paul Tesar, a geneticist at Case Western Reserve University, said that as scientists pushed the stem-cell-derived embryos further and further along the developmental path, the more they began to fuse- synthetic and natural embryos.
“There’s always going to be a gray area,” he said. “But as scientists and as a society we have to come together to decide where the line is and define what is ethically acceptable.”