VEGF-A and FGF-2 prime EC tube morphogenic responses to SCF, IL-3, and SDF-1α by up-regulating hematopoietic cytokine receptors. (A,B) ECs were primed for 16 hours with either control, VEGF/FGF, or SCF/IL-3/SDF-1α treatments and then were suspended in 3D collagen matrices with either control, VEGF, or SCF/IL-3/SDF-1α additions. Priming cues are listed first, followed by the morphogenic stimuli. Cultures were fixed after 72 hours, photographed, and quantitated for total EC tube area (n ≥ 10; P ≤ .01). Bar equals 100 μm. (C) Quail vitelline vessels were isolated and the vessels primed overnight with VEGF-A/FGF-2 or control conditions. Explants were placed into collagen gels and were treated with either VEGF-A, hematopoietic cytokines, or control conditions. After 5 days, the vessels were stained with QH-1 to visualize quail ECs and representative images are shown. Bar equals 75 μm. (D) Quantification of EC tube formation from vitelline vessel explants is shown (n ≥ 6; P ≤ .01). (E) Reverse transcription polymerase chain reaction analysis of EC mRNA primed with VEGF-A, FGF-2, or the combination of VEGF-A/FGF-2 versus control treated cells for 16 hours. (F) Western blot analysis of ECs primed with VEGF-A, FGF-2, or the combination of VEGF-A/FGF-2 versus control cells for 16 hours. (G) Western blot analysis of embryonic day 6 quail vitelline vessel explants primed with VEGF-A/FGF-2 versus nonprimed control vessels for 16 hours. *Denotes significance over control-control condition; ⁺denotes significance over the control-factors condition.