D849N-mutant PDGFR-beta increases the ratio of vessel area per tumor and average vessel area. Matrigel mixed with mock-transfected B16 melanoma cells was subcutaneously injected into mice and processed after 8 days as described in the legend of figure 2. Tissue sections were analyzed for the ratio of total vessel area/tumor (A), average vessel surface (B), number of vessels per high-power field (C) and numerical density of pericytes per perimeter of vessel (D). Asterisks indicate statistical significance (*, p < 0.01) by Student's t-test. Double immunohistochemical staining for vessels (CD31, blue) and perivascular cells (alpha-smooth muscle actin, brown) identify significantly larger vessels in B16 melanoma/matrigel plugs grown in wild type mice (E) compared to D849N-mutant mice (F) (the same magnification was used in Fig. 4E and Fig. 4F).