The goal, according to the scientists involved in the research, is not to create mice or babies outside the womb, but to revive understanding of how organs develop in embryos and to use this knowledge to develop new ways to heal people.
From a clump of embryonic stem cells, scientists at the Weizmann Institute of Science created synthetic embryos that closely resembled real mouse embryos, with rudimentary beating hearts, blood flow, folded brain tissue and intestinal tract. The mouse embryos developed in an artificial womb and stopped developing after eight days, about a third of a mouse pregnancy.
The decade-long advance comes in a field crowded with efforts to develop embryo models from human and mouse cells. Scientists can use these models to scrutinize the early stages of embryonic development and study organ formation.
But as the models get closer to reality, they also open up ethically murky territory. When do synthetic embryos become so similar to the real thing that they are subject to protections similar to those applied to real embryos?
“This is an important milestone in our understanding of how embryos are built,” Alfonso Martinez Arias, a developmental biologist at Pompeu Fabra University in Barcelona, who is not not involved in research. He called the experience a “game changer”.
The research, published Monday in the journal Cell, comes a long way from growing a mouse, let alone a human, outside the womb. It was a proof of concept that a complete synthetic embryo could be assembled from embryonic stem cells, and although the researchers succeeded, it was a very error-prone process, with only a small fraction of embryos developing. the beginnings of a beating heart and other organs.
Although synthetic mouse embryos closely resembled natural mouse embryos, they weren’t exactly the same and didn’t implant or result in pregnancies in real mice, according to stem cell scientist Jacob Hanna at the Weizmann Institute of Science who led the work.
“This is an interesting next step, not shocking, but one that makes more plausible in the long term a proposition with broad implications: the possibility of turning any mouse cell into a living mouse,” said Henry T. Greely, bioethicist at Stanford Law. School.
The research, like other recent studies, puts the possibility of a full human synthetic embryo on the horizon, several researchers said, making it necessary to continue a societal discussion about how these entities should be treated. . Last year, the International Society for Stem Cell Research relaxed a ‘historic 14-day rule’ that researchers could only grow natural embryos for 14 days in the lab, allowing researchers to seek approval for longer studies. It is prohibited to implant human embryo models in a uterus.
“The mouse is a starting point to think about how you want to approach this in humans,” said Alex Meissner, stem cell biologist at the Max Planck Institute for Molecular Genetics. “There’s no need to be alarmed or to panic, but…as we learn, it’s important to have the discussion side by side: how far do we want to go?
Hanna said he hoped the technology could be used not as a substitute for reproduction but as a way to create synthetic human embryo models that could result in organ precursors that could be studied and potentially used. for therapeutic purposes.
For decades, stem cell therapy’s main hope has been to repair the body’s own tissues. Stem cells can grow into any tissue or organ, so the possibility of using these cells to repair spinal cord injuries, repair damaged hearts, or cure diabetes is alluring. But transforming these cells into complex and functional tissues has been a challenge. Hanna’s hope is that watching this process unfold early in development will provide important clues.
“Our goal is not to make a pregnancy outside of the womb, whether it’s mice or any other species,” Hanna said. “We really face challenges in making organs – and for stem cells to become organs, we have to learn how the embryo does it. We started with that because the uterus is a black box, it doesn’t is not transparent.
Hanna founded a company, Renewal Bio, which plans to use the technology for therapeutic purposes. One possible use would be to take skin cells from a woman with fertility issues, reprogram those cells to create stem cells, and then develop synthetic embryo models that could be used to produce eggs.
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