Figure 6.

Expression pattern of the Dll4 gene suggests that it encodes the ligand for the Notch1 and Notch4 receptors in the embryonic vasculature. Whole-mount in situ hybridization with the indicated probes of embryos isolated at E8.5 (B,C), E9.5 (A,D–G), and E10.5 (H,I). Dll4 expression is observed in the dorsal aorta (arrowheads) and, at E9.5, the intersomitic vessels (A). The other genes encoding Notch ligands do not exhibit obvious expression in the vasculature at E9.5 (D–G). At E10.5, Dll4 expression is observed in the internal carotid artery (ica) (H), but is not observed in branches of the primary head vein (arrows in I), which express Kdr.