A group of scientists managed to create an entity very similar to an early human embryo, without using sperm, eggs or a womb.
The team from the Weizmann Institute, in Israel, affirms that his “model embryo”, made from stem cells, shares the characteristics of a real embryo of 14 days.
It even released hormones that came back positive on a pregnancy test in the lab.
The goal of embryo models is to offer an ethical way of understanding the first moments of life.
The first weeks after a sperm fertilizes an egg are a period of dramatic change: you go from a collection of indistinct cells to something that ends up being recognizable on an ultrasound.
This crucial period is one of the main sources of miscarriages and birth defects, but it is not well understood.
“It’s a black box: our knowledge is very limited,” says Professor Jacob Hanna of the Weizmann Institute of Science.
Embryo research is sensitive from a legal, ethical and technical point of view. But now there is a rapidly developing field that mimics natural embryonic development.
This research, published in the journal Nature, is described by the Israeli team as the first “complete” embryo model because it mimics all the key structures that arise in the early embryo.
It’s something that “has never been done before,” says Professor Hanna.
Instead of a sperm and an egg, the starting material was reprogrammed stem cells to acquire the potential to become any type of tissue in the body.
Chemicals were then used to induce these stem cells to become four types of cells found in the earliest stages of the human embryo:
* cells of epiblastwhich develop into the embryo proper (or fetus)
* cells of trophoblastwhich become the placenta
* cells of hypoblastwhich become the yolk sac
* cells of extraembryonic mesoderm
A total of 120 of these cells were mixed in a precise ratio.
About 1% of the mixture began the journey of spontaneously assembling into a structure that resembles, but is not identical to, a human embryo.
“The merit belongs to the cells: with the right mix and the right environment it just works,” says Professor Hanna. “It’s an amazing phenomenon.”
Embryo models were allowed to grow and develop until they were comparable to a 14-day embryo. In many countries, this is the legal limit for research with normal embryos.
Despite it being a late night video call, I can hear the passion with which Professor Hanna shows me the “exquisite architecture” of the embryonic model in 3D.
I can see the trophoblast, which would normally become the placenta, enveloping the embryo. And it includes the cavities that fill with the mother’s blood to transfer nutrients to the baby.
There is a yolk sac, which performs some of the functions of the liver and kidneys, and a bilaminar embryonic disc, one of the main features of this stage of embryonic development.
What are these models for?
The hope is that embryo models can help scientists explain how different types of cells arise, witness the first steps in the construction of the body’s organs, or understand hereditary or genetic diseases.
This study already shows that other parts of the embryo will not form unless the first cells of the placenta can surround it.
There is even talk of a possible improvement in the success rates of IVF if it is possible to understand why some embryos fail or if the models are used to check if the drugs are safe during pregnancy.
Professor Robin Lovell Badge, who researches embryonic development at the Francis Crick Institute, tells me that these embryo models “look very good” and “seem quite normal”.
“I think it’s good, it’s very well done, it all makes sense and I’m pretty impressed,” he says.
But the current 99% failure rate should be improved, he adds. It would be hard to understand what is going wrong with miscarriage or infertility if the pattern fails to form most of the time.
a legal window
The research also raises the question of whether embryonic development beyond 14 days could be mimicked.
This it would not be illegalsince embryo models are legally different from embryos.
“Some will embrace this, but others won’t like it,” says Professor Lovell Badge.
Professor Alfonso Martínez Arias, from the Department of Experimental and Health Sciences at the Pompeu Fabra University in Barcelona, affirms that this is “a very important research project”.
“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, he said, “thus opening the door to the study of the events that lead to the formation from the plane of the human body.
The researchers stress that it would be unethical, illegal, and indeed impossible to achieve a pregnancy using these models.: Assembling all 120 cells together goes beyond the point at which an embryo could successfully implant itself in the lining of the uterus.
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