Fig. 1. The extra-embryonic endoderm lineage and XEN cell cultures. (A) Schematic of an E4.5 blastocyst and an E5.5 embryo, illustrating the primitive, visceral and parietal endoderm (green). The trophoblast and epiblast lineages are represented in yellow and red, respectively. The proximodistal axis is indicated. ICM, inner cell mass. (B) Phase-contrast micrograph of XEN cells cultured at low density illustrating the refractile, rounded cell type and the epithelioid cell type. (C) XEN cells grown to near confluency showing the presence of individual cells and an epithelial sheet of cells. (D) XEN cells participating in a lattice-type structure. (E) XEN cells plated in the absence of gelatin resulted in differentiation of some cells into large vacuolated cells in 6 days. Scale bar: 10 µm for B-D; 40 µm for E.