Reconstruction of distinct vertebrate gastrulation modes via modulation of key cell behaviours in the chick embryo

The morphology of gastrulation driving the internalisation of the mesoderm and endoderm differs dramatically among vertebrate species. It ranges from involution of epithelial sheets of cells through a circular blastopore in amphibians to ingression of mesenchymal cells through a primitive streak in amniotes. By targeting signalling pathways controlling critical cell behaviours in the chick embryo, we generated crescent- and ring-shaped mesendoderm territories in which cells can or cannot ingress. These alterations subvert the formation of the chick primitive streak into the gastrulation modes seen in amphibians, reptiles and teleost fish. Our experimental manipulations are supported by a theoretical framework linking cellular behaviors to self-organized multi-cellular flows in the accompanying paper. All together, this suggests that the evolution of gastrulation movements are largely determined by the shape of and cell behaviours in the mesendoderm territory across different species, and controlled by a relatively small number of signalling pathways.