D849N-mutant PDGFR-beta results in increased pericyte coverage of vessels. B16 melanoma mock cells, which do not produce PDGF-BB, were subcutaneously injected and processed as described in the legend of figure 1. Double immunohistochemical staining for endothelial cells (CD31, blue) and perivascular cells (α-smooth muscle actin, brown) in B16 melanoma is shown. Please note the small vessels (blue) covered by few pericyte (brown) in tumors grown in wild type mice (A) compared to larger vessels surrounded by multiple perivascular cells (brown) in tumors grown in D849N-mutant mice (B). Tissue sections were analyzed for total vessel area (C), average vessel surface (D), number of vessels per high-power field (E) and numerical density of pericytes per vessel perimeter (F). Asterisk indicates statistical significance (*, p < 0.01) by Student's t-test.