The Endothelium: The Cradle of Definitive Hematopoiesis?

Abstract

It has been more than 80 years since a lineage relationship between hematopoietic and endothelial cells in the form of a bipotential precursor---the hemangioblast---was first proposed. Evidence has accumulated that supports the existence of such a cell, however, identification and isolation of hemangioblasts from embryos has so far not been achieved. The situation has been further complicated by the suggestion that different types of hemangioblasts with varying degrees of maturity exist, some of which may be restricted to either primitive or definitive hematopoietic lineages. Furthermore, recent work has pointed to a specialized group of endothelial cells that possess hemogenic potential and may represent an intermediate step in the generation of definitive hematopoietic stem cells. The following chapter provides a brief summary of recent developments in the investigation into the origins of hematopoiesis.