Model of the emergence of hemogenic endothelium in the YS blood islands from mesodermal precursors. A model is proposed incorporating the concepts established in previous studies and in the present work.^8-10,17  Precursors of endothelium (blue) and blood (red) derive from adjacent regions of the E6.5 mouse epiblast.⁸  Blood precursors would be the first to ingress the PS, followed by endothelial precursors. Both lineages colonize the YS and form the blood islands through cell-cell interactions between the 2 lineages. Interspersed endothelial cells in the blood islands become hemogenic and give rise to CD41⁺ Runx1⁺ hematopoietic clusters (orange). Ant, anterior; EE, extra-embryonic; Ep, epiblast; Post, posterior.