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Scientists have created synthetic embryos that resemble human ones, albeit primitive ones. As NPR's Rob Stein reports, the experiment raises some tricky ethical questions.
ROB STEIN, BYLINE: For decades, scientists have been trying to understand how exactly a human embryo becomes a human being. But Ali Brivanlou of the Rockefeller University in New York says some of the most crucial moments of that journey have always been a mystery.
ALI BRIVANLOU: The earliest stages of development, so far it has been a complete black box.
STEIN: Because during many of the most crucial early stages, embryos are inside a woman's womb. And scientists aren't supposed to study them in their labs.
BRIVANLOU: And so we came up with a model of human embryos that is developed outside of the womb and is not the product of sperm and eggs, but the product of human embryonic stem cells that self-organize into complicated structures.
STEIN: Brivanlou and his colleagues put human embryonic stem cells into dishes in their lab and use chemical signals to coax them into organizing themselves into three-dimensional hollow balls that resemble early embryos. And in the journal Nature Cell Biology, they report these embryoids then took a crucial next step. They did what's called breaking the symmetry of that sphere.
BRIVANLOU: This process of symmetry-breaking is a major Holy Grail of developmental biology.
STEIN: Because that's what starts the process of separating our heads from our bottoms, our right sides from our left, our fronts from our back to eventually create an entire human being.
BRIVANLOU: Life is a continuation of symmetry-breaking events.
STEIN: And Brivanlou says finally being able to recreate and now begin to study that first symmetry-breaking moment is both thrilling and humbling.
BRIVANLOU: I really feel like I'm looking at one of the most mysterious aspects of our own existence, which happens in the place called the womb, that otherwise would have never had access to it. And every day that I come to my lab and I look down at the microscope, I know that my eyes are going to see something that no other human beings have seen before.
STEIN: And Brivanlou hopes these embryoids could eventually reveal all kinds of things - how to treat infertility; prevent miscarriages, birth defects.
BRIVANLOU: So it's extremely exciting.
STEIN: Other scientists agree. George Daley is the dean of the Harvard Medical School.
GEORGE DALEY: Scientifically, this is important because we really don't have access to the earliest stages of human development. And so here we have this, you know, remarkable tool in a petri dish.
STEIN: But Daley and others acknowledge that this kind of research could start to raise some red flags.
INSOO HYUN: It does send folks down the road to thinking very seriously about where limits may be ethically for this work.
STEIN: Insoo Hyun is a bioethicist at Case Western Reserve University and Harvard.
HYUN: As the embryo models become much more complete and much further along in showing us how the human body develops after fertilization, one might begin to wonder - at what point do these models effectively just become the real thing?
STEIN: Now, Brivanlou says that his embryoids could never become a baby. But the scientists are trying to create synthetic embryos that are even closer to the real thing.
Rob Stein, NPR News.
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