Fig. 8. A genetic mutation in the VEGF receptor Flk1 blocks neural tube-derived vascular plexus formation. Mouse presomitic mesoderm explants were cultured for 72 hours in basal medium with either 30 ng/ml VEGFA (A,B) or stage HH10-13 quail neural tubes (C,D). Explants were either Flk1^+/– (A,C) or Flk1^–/– (B,D), and mouse vascular cells were visualized by ß-gal staining. The arrows (A,C) indicate mouse vascular plexus, and the arrowheads (B,D) point to ß-gal positive (blue) presumptive mouse vascular cells. n7 for all conditions. Scale bar: 200 µm for all panels.