The first synthetic embryos developed ex utero reach the stage of organ growth

The black box is barely larger than a crate of wine. The top side, transparent, reveals a wheel that rotates several tubes where tiny balls float in yellowish liquid: these are embryos in full growth. The machine is a kind of artificial uterus that reproduces the conditions of in utero gestation, invented by Professor Jacob Hanna and his team at the Weizmann Institute of Science in Rehovot, Israel. Last year, they grew mouse embryos there, born from a classic fertilization. Now they are growing “synthetic embryos”, created from stem cells, without gametes – the sex cells – or fertilization. The researchers managed to make them develop for up to eight and a half days, a world first unveiled at the beginning of August.

A few days later, the magazine Nature published similar results, to which the Israeli team contributed, testifying to the effervescence and the intense mixture of competition and cooperation that has animated this field in recent years.

In both cases, the breakthrough concerns both the method of obtaining and the duration of culture: at this stage, the embryoids already have a developed brain, a beating heart, intestines, the “somites”, which will give the muscles, as well as a placenta. They are 95% similar to natural mouse embryos at this stage of maturation, the complete gestation in the rodent being twenty days.

New Horizons

The method can be transposed to humans: the Israeli team has already grown “synthetic embryos, at a very early stage”which are currently still very different from what nature produces, says Professor Jacob Hanna. Beyond the technical and scientific prowess, his study on the mouse, which aroused a lot of fantasies after its publication in the journal Cell1^er August, suggests new horizons, in particular to better understand the stages of embryo development, and in the field of fertility or regenerative medicine.

These “synthetic embryos” – synthetic embryosas they are named in Cell – will not be able to carry out a complete gestation and become humans and mice, emphasizes Professor Hanna from the outset. He himself also hesitates on the appropriate term to designate them, because they are not made from an assembly of cells, like other models of embryos obtained artificially, but are not natural for all that. The 43-year-old scientist evokes ” embryoids”, because they “are far behind the embryos [issus d’une fécondation]. They can only grow in vitro for up to eight and a half days, compared to eleven days for embryos obtained by fertilization. This is the maximum, for now. Beyond, [on] can’t[t] even call them embryos because they have so many malformations”. Only 0.5% of the entities recreated in this way grow – a low success rate which does not worry the team, because, at such an early stage, the researchers can cultivate them en masse.

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