Fig. 5. Changes in the extent of the mesendoderm territory and the degree of EMT could underlie the evolution of vertebrate gastrulation.

(A) Evolutionary relationships of representative vertebrate morphologies recapitulated in the chick embryo via modification of key cell behaviors. Images of gastrulation showing the blastopoal canal in chameleon (28 days), the blastopore in Xenopus (12 hours), and the germ ring in zebrafish (5.7 hours) are adapted from (33, 44, 49). Scale bars, 250 μm. (B) SNAI2⁺ cell distributions in HH3⁺ chick embryos after different treatments show that manipulating the extent of the mesendoderm territory and the level of EMT controlling ingression in the chick embryo reproduce critical morphological structures of gastrulation in other vertebrates. Scale bars, 500 μm (chick embryos).