Expression of alpha 4-integrin defines the earliest precursor of hematopoietic cell lineage diverged from endothelial cells

Embryonic stem cells can differentiate in vitro into hematopoietic cells th rough two intermediate stages; the first being FLK1(+) E-cadherin(-) proxim al lateral mesoderm and the second being CD45(-) VE-cadherin(+) endothelial cells. To further dissect the CD45(-) VE-cadherin(+) cells, we have examin ed distribution of alpha 4-integrin on this cell population, because alpha 4-integrin is the molecule expressed on hematopoietic stem cells. During cu lture of FLK1(+) E-cadherin(-) cells, CD45(-) VE-cadherin(+) alpha 4-integr in(-) cells differentiate first, followed by alpha 4-integrin(+) cells appe aring in both CD45- VE-cadherin+ and CD45(-) VE-cadherin(-) cell population s. In the CD45(-) VE-cadherin(+) cell population, alpha 4-integrin(+) subse t but not alpha 4-integrin(-) subset had the potential to differentiate to hematopoietic lineage cells, whereas endothelial cell progenitors were pres ent in both subsets. The CD45(-) VE-cadherin(-) alpha 4-integrin(+) cells a lso showed hematopoietic potential. Reverse transcription-polymerase chain reaction analyses showed that differential expression of the Gata2 and Myb genes correlated with the potential of the alpha 4-integrin(+) cells to giv e rise to hematopoietic cell differentiation. Hematopoietic CD45(-) VE-cadh erin(+) alpha 4-integrin(+) cells were also present in the yolk sac and emb ryonic body proper of 9.5 day postcoitum mouse embryos. Our results suggest that the expression of alpha 4-integrin is a marker of the earliest: precu rsor of hematopoietic cell lineage that was diverged from endothelial proge nitors. (C) 1999 by The American Society of Hematology.