The study, published in Nature, found that mouse embryonic stem cells could organise themselves along three axes: left and right, top half and lower half, and front and back.
'You would expect to get sort of a mess, sort of a tumour, but no – you get something that is very highly organised,' study author Dr Denis Duboule of the University of Geneva and the Ecole Polytechnique Fédérale de Lausanne in Switzerland, told Science magazine. 'They make a little banana or a little zucchini.'
The finding is significant because in an embryo, these axes are crucial for guiding the body plan of a developing organism. Genetic analysis showed that the gene expression in the gastruloids was also similar to that found in a developing embryo.
Researchers involved in this study had previously found in 2014 that clusters of 250-300 embryonic stem cells from mice could self-organise and form gastruloids. This self-organisation was stimulated when the researchers exposed the cells to a chemical that turned on a signalling pathway called Wnt.
However, embryonic stem cells have so far not been capable of developing into a full embryo on their own. This left scientists to think that external cues from other parts of the embryo or from the uterus were necessary to help embryonic cells come together to make an organism. The present study suggests that embryonic stem cells are less reliant on external cues to form an organism than previously thought.
'This is a fascinating study,' Dr James Briscoe at the Francis Crick Institute in London, who was not involved in the research, told The Scientist. 'The ability of [embryonic stem] cells, when properly shepherded, to specify all three major body axes is striking and is yet another example of the surprising ability of developing tissues to self-organize.'
There are still many differences between gastruloids and embryos. While the overall structure of the gastruloid may have similarities to embryos, their fine-scale structure within the cell layers is very different. In a gastruloid, these layers are extremely disoragnised compared with an embryo. As Dr Briscoe said: 'It's as if Picasso decided to become an embryologist.'