Figure 6.

Notch1 and Dll4 are expressed at different levels in different cells but at high levels in the same cell of the developing arteries. (A-C) In situ hybridization on consecutive cryosections of 8.75 dpc (12 ss) Dll4^+/+ embryos showing that Notch1, Dll4 and Hey1 are expressed (red) in almost all aortic endothelial cells. (D-F) Double in situ hybridization for Notch1 and Dll4 reveals that these genes are expressed at high levels in the same cells. Note also that Notch1 is weakly expressed on the anterior cardinal veins (v), where there is no expression of Dll4. (G-I) In the Dll4^-/- embryos the Notch1 receptor is still expressed on dorsal aortae (da) but there is no detectable endothelial expression of the effector Hey1 (I), although its expression remains in the pericardium (p). (Scale Bars: 50 μm).