The model structures, each grown from a single embryonic stem cell, reached the beginning of a developmental milestone known as gastrulation, when the embryo transforms from being a continuous sheet of cells to forming distinct cell lines and setting up the basic axes of the body. At this stage, the embryo does not yet have a beating heart, gut or beginnings of a brain, but the model showed the presence of primordial cells that are the precursor cells of egg and sperm.
“Our human model is the first three-lineage human embryo model that specifies amnion and germ cells, precursor cells of egg and sperm,” Żernicka-Goetz told the Guardian before the talk. “It’s beautiful and created entirely from embryonic stem cells.”
The development highlights how rapidly the science in this field has outpaced the law, and scientists in the UK and elsewhere are already moving to draw up voluntary guidelines to govern work on synthetic embryos. “If the whole intention is that these models are very much like normal embryos, then in a way they should be treated the same,” Lovell-Badge said. “Currently in legislation they’re not. People are worried about this.”
There is also a significant unanswered question on whether these structures, in theory, have the potential to grow into a living creature. The synthetic embryos grown from mouse cells were reported to appear almost identical to natural embryos. But when they were implanted into the wombs of female mice, they did not develop into live animals. In April, researchers in China created synthetic embryos from monkey cells and implanted them into the wombs of adult monkeys, a few of which showed the initial signs of pregnancy but none of which continued to develop beyond a few days. Scientists say it is not clear whether the barrier to more advanced development is merely technical or has a more fundamental biological cause.
“That’s very difficult to answer. It’s going to be hard to tell whether there’s an intrinsic problem with them or whether it’s just technical,” Lovell-Badge said. This unknown potential made the need for stronger legislation pressing, he said.
