Macrophages promote SVP angiogenesis independently of VEGF. (A-F) Hindbrains (11.5 dpc) were labeled for IB4 and F4/80; (D-F) higher magnifications of the boxed areas in (A-C). Controls (no Cre; A,D) were compared with littermates with a knockdown of VEGF in neural progenitors (Nes^CreVegfa^fl/+; B,E) and stage-matched mutants lacking VEGF164 only (Vegfa^120/120; C,F). Scale bar represents 100 μm. (G) Quantitation of the number of vascular intersections and macrophages (Mϕ) in the SZ at 11.5 dpc; n = 3. Error bars represent SD of the mean. The P values were determined by comparing both types of mutants to Vegfa^fl/+ hindbrains lacking Cre. (H) Quantitation of Vegfa mRNA levels relative to Actb (β-actin) in PU.1-deficient and wild-type littermate hindbrains at 11.5 dpc. The horizontal lines indicate the mean; n = 3.