Sections through Ac-LDL-DiI–inoculated embryos 1 hour after inoculation. Sections are 7 μm thick. (A-B) Cross-section at the level of the dorsal aorta. (A) Phase contrast. (B) Fluorescence revealing the DiI signal. Boxes in panels A and B indicate the region magnified in panel B. The signal is restricted to the internal-most cells, thus the endothelial layer. (C-D) Cross-section at the midtrunk level. (C) Phase contrast. (D) DiI. Boxes in panels C and D indicate the region magnified in panel D. DA indicates dorsal aorta; NT, neural tube. For all images, original magnification, × 40.