The Notch ligand DLL4 specifically marks human hematoendothelial progenitors and regulates their hematopoietic fate Ayllon, Veronica Bueno, Clara Ramos Mejía, Verónica Navarro-Montero, Oscar Prieto, Cristina Real Luna, Pedro José Romero, Tamara García-León, María José Toribio, Maria Luisa Bigas, Anna Menendez, Pablo Notch signaling is essential for definitive hematopoiesis, but its role in human embryonic hematopoiesis is largely unknown. We show that in hESCs the expression of the Notch ligand DLL4 is induced during hematopoietic differentiation. We found that DLL4 is only expressed in a sub-population of bipotent hematoendothelial progenitors (HEPs) and segregates their hematopoietic versus endothelial potential. We demonstrate at the clonal level and through transcriptome analyses that DLL4(high) HEPs are enriched in endothelial potential, whereas DLL4(low/-) HEPs are committed to the hematopoietic lineage, albeit both populations still contain bipotent cells. Moreover, DLL4 stimulation enhances hematopoietic differentiation of HEPs and increases the amount of clonogenic hematopoietic progenitors. Confocal microscopy analysis of whole differentiating embryoid bodies revealed that DLL4(high) HEPs are located close to DLL4(low/-) HEPs, and at the base of clusters of CD45+ cells, resembling intra-aortic hematopoietic clusters found in mouse embryos. We propose a model for human embryonic hematopoiesis in which DLL4(low/-) cells within hemogenic endothelium receive Notch-activating signals from DLL4(high) cells, resulting in an endothelial-to-hematopoietic transition and their differentiation into CD45+ hematopoietic cells. 2026-02-26T13:36:32Z 2026-02-26T13:36:32Z 2015-08 journal article Ayllon, V.; Bueno, C.; Ramos Mejía, V. [et al.]. (2015). The Notch ligand DLL4 specifically marks human hematoendothelial progenitors and regulates their hematopoietic fate. Leukemia, vol. 29, 1741–1753. doi:10.1038/leu.2015.74 1476-5551 0887-6924 https://hdl.handle.net/10481/111607 10.1038/leu.2015.74 eng embargoed access Springer Nature