Emergence of the endothelial network during embryonic development.

The avian model provides an experimental approach for dissecting the origin , migrations, and differentiation of cell lineages in early embryos. In thi s model, the endothelial network was shown to stem from both the somites an d the splanchnopleural mesoderm. The somite line age produces only endothel ial cells, whereas the splanchnopleural line age also produces hematopoieti c stem cells. Potentialities of the mesoderm are determined by a positive i nfluence from the endoderm and a negative influence from the ectoderm. A no vel mode of blood-borne angiogenesis is also described.