The emergence of the endothelial cell lineage in the chick embryo can be detected by uptake of acetylated low density lipoprotein and the presence of a von Willebrand-like factor.

Vascular endothelial cells from 3- to 10-day-old chicken embryos were identified by the uptake of acetylated low density lipoprotein (Ac-LDL) and the presence of a von Willebrand-like factor. These were determined on cross sections of aortic arches as well as in cell cultures prepared from the arches. To visualize the uptake of Ac-LDL, the fluorescent probe 1,1'-dioctadecyl-1-3,3,3',3'-tetramethyl-indo-carbocyanine perchlorate-Ac-LDL (DiI-Ac-LDL) was used. Following injection of the DiI-Ac-LDL probe into the embryonic heart, the endothelium of the aortic arches became specifically labeled. Also, following the administration of the probe to cell cultures, about 5-10% of the cells became DiI-positive. Indirect immunofluorescence with an antibody against von Willebrand (vW) factor also revealed specific staining of the endothelium of the aortic arches as well as of a subset of cells in cultures from aortic arches. These two histochemical markers were further used to identify the emergence of the endothelial cell lineage in the chicken blastodisc. Cultured cells from embryos incubated in ovo for 16 hr exhibited both uptake of DiI-Ac-LDL and expression of a vW-like factor. The proportion of these cells was about 30% of the total cultured cells and increased to over 50% in cultures of embryos incubated in ovo for 20 hr. However, cells positive for uptake of DiI-Ac-LDL and expression of vW-like factor were lacking in cultures of unincubated eggs or eggs incubated for 6-10 hr. We conclude that the very early endothelial cells in the chick blastodisc are already capable of expressing characteristic properties of vascular endothelium.