Developmental relationship between hematopoietic and endothelial cells.

Blood (hematopoietic cells) and blood vessels (endothelial cells) develop from mesoderm via a transitional progenitor known as the hemangioblast. Flk-1, a receptor tyrosine kinase, and Scl, a basic helix-loop-helix transcription factor, are two critical molecules functioning in this process. Recent studies have shown that Flk-1 expressing mesoderm contributes to the circulatory system, including hematopoietic, endothelial, smooth muscle, skeletal muscle, and cardiac muscle cells. Our studies suggest that hemangioblast specification within Flk-1 expressing mesoderm is regulated by Scl expression. Herein, we review studies that have utilized transgenic mouse models as well as an in vitro model of embryonic stem cell differentiation, both of which have greatly contributed to the current understanding of the cellular and molecular pathways regulating hemangioblast development and differentiation.