Hemogenic activity of E8.5 YS endothelium. (A-B) Examples of high-resolution 3D confocal reconstruction of the YS blood island region at E8.5, showing recombined endothelial and hematopoietic cells (EYFP) after (A) Tie2CreERT2-induced recombination (polyclonal frequency) or (B) VavCre-induced recombination. (C-D) EYFP⁺ Lyve1⁺ endothelial cells (open arrowhead) in close association with EYFP⁺ blood cells (filled arrowhead). (E-F) Average number of EYFP⁺ blood cells within 1 to 2 cell diameters of EYFP⁺ or EYFP⁻ endothelial cells (left), and the frequency of EYFP⁺ or EYFP⁻ endothelial with EYFP⁺ blood cells within 1 to 2 cell diameters. (See also supplemental Figure 3 and supplemental Movies 1-2.) Fluorescence from EYFP, Cy3, Cy5, and DAPI in (A-D) was acquired with a Nikon confocal A1-R equipment using a 40X/1.30 NA oil objective at room temperature. All 3D reconstructions and videos were done using the NIS Elements AR 3.22.08 software. Endo, visceral endoderm.