Cell-state transitions and collective cell movement generate an endoderm-like region in gastruloids
Shaping the animal body plan is a complex process that involves the spatial organization and patterning of different layers of cells. Recent advances in live imaging have started to unravel the cellular choreography underlying this process in mammals, however, the sequence of events transforming an unpatterned group of cells into structured territories is largely unknown. Here, using 3D aggregates of mouse embryonic stem cells, we study the formation of one of the three germ layers, the endoderm. We show that the endoderm can be generated from an epiblast-like state by a three-tier mechanism: a release of islands of E-cadherin expressing cells, their flow toward the tip of the 3D aggregate, and their segregation. In contrast to the prevailing view, this mechanism does not require epithelial to mesenchymal transitions and vice-versa but rather a fragmentation, which is mediated by Wnt/β- catenin, and a sorting process. Our data emphasize the role of signaling and cell flows in the establishment of the body plan. ### Competing Interest Statement The authors have declared no competing interest.
