The majority of cells migrating from the VBI are myeloid. (A) Schematic of transplant of lineage labeled VBI tissue to unlabeled recipient embryo. (B-C) Red light images showing migration of lineage labeled cells from the VBI implant and VP implant, respectively. (B′-C′) Image reversal of B and C to enhance visualization of labeled cells. (D) Quantitation of labeled cells per embryo migrating from the VBI and VP implants at early tailbud (st24). (E-L) In situ hybridization detection of myeloid cells using spib and runx1 probes. The pattern of distribution and time of emigration from the VBI of lineage labeled cells closely resembles the spib/runx1⁺ population. (M-O′) Myeloid cells in lineage-traced embryos were detected by double in situ hybridization with combined runx1 and spib probes (blue cells). Cells migrating from the VBI were detected by red filter imaging. Higher magnification of boxed region is shown in M′-O′. Note that most lineage-traced cells were positive for the myeloid probes (yellow circle), whereas a small proportion was not (white circle). (P) Single frame from supplemental Video 2 of lineage labeled embryo from st36-42. Cells paths were tracked using MTrackJ.¹⁸  All labeled cells were observed to migrate over time, consistent with blood, but not EC behavior.