[1][2][3] In the mouse embryo, the emergence of blood islands in the yolk sac at embryonic day 7 marks the onset of hematopoiesis.
Hemangioblasts have been first extracted from embryonic cultures and manipulated by cytokines to differentiate along either hematopoietic or endothelial route.
It was then found that hemangioblasts are also present in the tissue of post-natal individuals, such as in newborn infants and adults.
Existence of the hemangioblast was first proposed in 1917 by Florence Sabin, who observed the close spatial and temporal proximity of the emergence of blood vessels and red blood cells within the yolk sac in chick embryos.
By using limiting dilutions, the authors demonstrated that the resulting hematopoietic and endothelial cells were indeed of clonal origin, proving that they had successfully isolated the hemangioblast in the developing embryo.