• Written by James Gallagher
  • Health and science reporter

image source, Weizmann Institute of Science

photo caption,

A model of a human embryo derived from stem cells showing blue cells (embryo), yellow cells (yolk sac), and pink cells (placenta).

Scientists have succeeded in developing an entity that closely resembles an early human embryo, without the use of sperm, eggs or a uterus.

The Weizmann Institute team says the ‘model embryo’, made using stem cells, looks like a textbook example of a real 14-day-old fetus.

It even released hormones that made the pregnancy test positive in the lab.

The ambition of embryo models is to provide an ethical way to understand the first moments of our lives.

The first weeks after a sperm fertilizes an egg is a period of dramatic change — from an inconspicuous collection of cells to something eventually recognizable by a baby’s examination.

This crucial time is a major source of miscarriage and birth defects but is poorly understood.

“It’s a black box,” Professor Jacob Hanna of the Weizmann Institute of Science tells me. “It’s not a cliché, our knowledge is very limited.”

Starting tools

Embryo research is risky legally, ethically and technically. But now there is a rapidly developing field that mimics the development of normal embryos.

The Israeli team described the research, which was published in the journal Nature, as the first “complete” embryonic model to simulate all the major structures seen in the early embryo.

“It’s actually a typical picture of a 14-year-old human fetus, which hasn’t been done before,” says Prof Hannah.

Instead of sperm and an egg, the starting material was naïve stem cells that had been reprogrammed to gain the ability to become any type of tissue in the body.

Chemicals were then used to transform these stem cells into four types of cells found in the early stages of the human embryo:

  • ectodermal cells, which become a healthy embryo (or fetus)
  • trophoblast cells, which become the placenta
  • cells under the blastula, which become the supporting yolk sac
  • Mesoderm cells outside the embryo

A total of 120 of these cells were mixed in a minute ratio, and then the scientists stepped back and watched.

About 1% of the mixture began spontaneously assembling into a structure resembling, but not identical to, a human embryo.

“I give the cells great credit – you have to get the right mix and the right environment, and the process will begin,” says Prof Hannah. “This is an amazing phenomenon.”

Embryo samples were allowed to grow and develop until they were comparable to an embryo 14 days after fertilization. In many countries, this is the legal limit for normal embryo research.

Despite my late-night video call, I can hear the excitement as Prof. Hanna gives me a 3D tour of the “wonderful architecture” of the embryo model.

I can see the trophoblast, which usually becomes the placenta, enveloping the fetus. They include cavities – called lacunae – which are filled with the mother’s blood to transfer nutrients to the baby.

There is a yolk sac, which performs some of the roles of the liver and kidneys, and a bilaterian embryonic disc – one of the defining features of this stage of fetal development.

The hope is that embryo models will help scientists explain how different types of cells emerge, witness the first steps in building organs, or understand hereditary or genetic diseases.

And this study already shows that other parts of the fetus will not form unless cells from the early placenta can surround it.

There is even talk of improving IVF success rates by helping to understand why some embryos fail or using models to test whether drugs are safe during pregnancy.

Professor Robin Lovell-Badge, who researches embryonic development at the Francis Crick Institute, told me that these embryo models “look very good” and “look very normal”.

“I think it’s a good thing, I think it’s done very well, everything makes sense and I really like it,” he says.

He adds that the current failure rate of 99 percent needs improvement. It would be hard to understand what goes wrong with miscarriages or infertility if the model fails to compile itself most of the time.

legally distinct

This work also raises the question of whether fetal development beyond the 14-day stage can be simulated.

This would not be illegal, even in the UK, as embryo models are legally different from embryos.

“Some people will like it, but others won’t,” says Professor Lovell-Badge.

The closer these models are to an actual embryo, the more ethical questions they raise.

They’re not normal human embryos, they’re embryo models, but they’re very close.

“Should you regulate it in the same way as a normal human fetus or can you be more relaxed about how you treat it?”

This is “the most important research,” said Professor Alfonso Martinez Arias, from the Department of Experimental and Health Sciences at Pompeu Fabra University.

“The work has achieved, for the first time, a faithful construction of the complete structure (of a human embryo) from stem cells” in the laboratory, which opens the door to studies of the events that led to the formation of man. body plan,” he said.

The researchers stress that it would be unethical, illegal and, in fact, impossible to achieve pregnancy using these embryo models, as putting together 120 cells would exceed the point at which an embryo can successfully implant into the lining of the uterus.

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