L'Embryos reveals a new superpower! The embryonic stage is probably the most mysterious of our existence. In just a few days, a single cell multiplies and organizes itself at high speed, forming the fetus (which already has all our organs of forms) in just eight weeks. A crazy race that does not make it easy for us to observe all these stages. To study it, researchers can now grow in the lab very realistic imitations of the embryo. With which they finally begin to reveal all the secrets of this vital period.
One of these secrets was presented on September 26, 2024 in the journal Cellular Thanks to a collaboration between the Institute of Molecular Biotechnology of the Austrian Academy of Sciences, the Max Planck Institute in Germany and the Free University of Berlin. Using one of these mock embryos, the researchers have shown that it may be possible to pause human embryonic development, as can happen in other species.
A break to give the next baby a better chance
This phenomenon, called embryonic diapause, consists of significantly slowing down, or even stopping, the development of the embryo at a specific moment. This pause is triggered by hormonal changes, which lead to a reprogramming of the embryo to slow down its metabolism. But these changes are reversible, the embryo only waiting for a signal to start up again. In some animals, this pause is an obligatory stage of their embryogenesis.
While in others, such as mice, it is optional and occurs only when it is appropriate to delay delivery, for example due to harsh environmental conditions. Giving a better chance of survival to the future baby.
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Human embryos are also capable of making this pause.
In mouse embryos, this pause can be triggered in vitro by inhibiting mTOR, an enzyme that regulates cell proliferation and growth. This blocks development at the blastocyst level, when the embryo has only about a hundred cells, before its implantation in the uterus. The researchers wanted to know if this same strategy would have the same result in human embryos, by treating embryoids (synthetic embryos) at the blastocyst stage with an mTOR inhibitor (RapaLink-1).
And indeed, inhibiting this enzyme significantly slowed down the development of the embryoid and prevented it from attaching to endometrial cells (which line the uterus). Better still, this human embryonic model in pause mimicked very well what has already been observed in the mouse embryo during embryonic diapause, including the change in the level of expression of a large number of proteins.
And as in mice, this artificial diapause in human embryos was also reversible: it was enough to stop the mTOR inhibitor treatment for the development of the embryoid to resume where it had stopped. Even regaining the ability to adhere to endometrial cells, even if their efficiency in doing so remained lower than that of embryos never treated with the inhibitor.
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These embryonic pauses could improve the efficiency of in vitro fertilizations
These results show that the human embryo could also undergo these embryonic diapauses, even if this has never been observed in our species. This may be a remnant of the evolutionary process that we no longer use., speculates in a communicates Nicolas Rivron, director of the synthetic development laboratory at the Institute of Molecular Biotechnology of the Austrian Academy of Sciences and author of the study. Even though we have lost the ability to naturally enter this state of pause, these results suggest that we have retained the possibility of doing so. The and that we could trigger it. »
Which could be useful in some cases, such as when In vitro fertilization (IVF). "Inducing these pauses could give us more time to assess the health of the embryo before implantation and allow us to better synchronize it with the mother to improve the chances of implantation in the uterus."
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