BMP4 signaling directs primitive endoderm-derived XEN cells to an extraembryonic visceral endoderm identity

► BMP signaling promotes extraembryonic endoderm stem (XEN) cell epithelialization. ► BMP4-treated XEN cells acquire an extraembryonic visceral endoderm identity. ► Effect of BMP4 is reversible and is antagonized by LIF signaling. ► Fluctuation of Afp::GFP expression reveals a dynamic equilibrium upon BMP4 stimulation. ► XEN cells promote primitive erythroid progenitor (EryP) expansion.