Notch pathway activation in the NRV. (A-O) Single channel or merged confocal z-stack projections of double transgenic embryos carrying kdrl:Hsa.HRAS-mCherry (red) and Tp1bglob:eGFP (green) transgenes. (A-C) At 23 hpf, the CrDI (arrowhead) expresses EGFP whereas the PMBC (arrows in A and C) does not. (D-I) At 31–33 hpf the NRV is close to connecting to the CrDI (D-F) or has already connected (G-I). EGFP expression can be seen in one of the leading cells of the NRV (arrows in D-F). Insets are higher magnification of the region the arrows point at and are 4 μm single confocal sections. EGFP expression becomes clearer throughout the NRV once it is connected to the CrDI (arrows in G-I). (J-O) Control (J-L) and MO1-tnnt2a injected (M-O) embryos at approximately 52 hpf. EGFP expression in the NRV (arrows) is evident in injected embryos. HA, hyaloid artery. All images are lateral views, anterior to the left, dorsal up. CrDI, cranial division of internal carotid artery; DRV, dorsal retinal vessel; HA, hyaloid artery; NRV, nasal radial vessel; PMBC, Primordial midbrain channel; VRV, ventral radial vessel. Scale bars are 50 μm.