An embryo goes through various stages of development before becoming a full-fledged human. The later stages in utero are fairly well understood by modern medicine, but the same cannot be said for gastrulation which occurs just days after the egg is fertilized. An English study allows us to see a little more clearly.
Gastrulation corresponds to the second phase of embryonic development. This is the period during which the blastomeres (the cells from the first divisions of the fertilized egg) will divide into two or three layers:an outer layer (ectoderm), a middle layer (mesoderm, present only in triploblastics) and an inner leaflet (endoderm). Concretely, during this phase, an embryo is transformed from a one-dimensional layer.
Gastrulation begins between the fourteenth and fifteenth day of the cell cycle. Until now, however, researchers have very rarely had "access" to this process. In general, scientists are in fact not allowed to cultivate embryos in the laboratory for more than fourteen days for ethical reasons, since it is established, at least in mice, that gastrulation also marks the development of the system nervous .
For the first time, researchers at the University of Cambridge have actually been able to observe what happens in the gastrulation phase by studying a human embryo approximately sixteen to nineteen days proposed by a woman who decided to terminate her pregnancy and donate it to science.
After dissecting the sample consisting of about a thousand cells, the researchers used a genetic technique of single-cell RNA sequencing. The latter told them which genes were activated in each of these individual cells when they transformed into specialized cells.
These analyzes showed that gastrulation was very similar to that observed in mouse embryos, with two differences. For one thing, the first forms of blood cells appear visibly earlier in humans than in mice. And secondly, and perhaps more importantly, this particular embryo had not yet started the neurulation stage , during which the central nervous system is set up, unlike mice which form their first neurons in the second week of gestation.
In other words, in addition to offering us a unique insight into a central, but inaccessible stage of our development, this dataset invites us to question the limit of fourteen days for embryo culture, which could have a profound impact on research and medicine in general.
Details of the study are published in Nature.
