VA-associated HCs are functional. (A) Dissected VAs were cultured in methylcellulose and formed distinct colonies of BFU-e, Mac, and mixed colonies of granulocyte/macrophage with or without erythroid (Mix). (Top panels) Colony morphology. (Bottom panels) Cytospins of each colony type after Giemsa stain (purple). Scale bars as labeled per row. (B) Colony formation ability of the VA (in purple) is compared with the fetal liver (FL, in blue) during VA remodeling. A peak in VA colony activity is seen at E10 to E10.5 corresponding to the major vascular remodeling events, and is comparable with the fetal liver at this time point. By E10.5 to E11, the ability of the VA to form hematopoietic colonies is dramatically reduced. Error bars are average of triplicate cultures of n = 2 litters (each litter pooled separately per time point ± SEM). (C) VAs and fetal livers (FL) of VE-cadherin Cre crossed to R26R LacZ lines at E10.5 were collected (pooled together in single suspension, 1 litter each) and evaluated by FACS analysis for LacZ activity (FDG, left panel). Endothelial derived (FDG⁺) cells make up 60% of the collected cells, and within that population the stem cell markers c-kit and CD34 are highly expressed (right panel, percentage labeled per quadrant). The VA hematopoietic population surface marker expression very closely resembles the FL at this time point.