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At this point gastrulation begins and the so-called germ layers form.

For instance, the work called into question whether sharing a germ layer would always ease direct reprogramming between cell types.

In gastrulation, the epiblast differentiates into the three germ layers of cells — the ectoderm, mesoderm and endoderm — that will form the fetus.

Symmetry breaking, germ layer specification and axial organisation in aggregates of mouse embryonic stem cells.

It would be more revealing, he adds, to track later developmental events, such as the formation of the three germ layers that give rise to different organs, because these events are less governed by luck.