Pericyte association regulates expression of VEGF-A in ECs. (A) VEGF-A is expressed in a subset of ECs (arrows) in PNET from RIP1-Tag2 mice, as assessed by double in situ hybridization for VEGF-A (red) and Flk1 (green). Note that VEGF-A is abundantly expressed by tumor cells, as expected (stars). Cell nuclei (DAPI), blue. Original magnification, 400×. The panel is representative of at least 5 fields in 5 tissue sections taken from 5 mice. (B) Expression of VEGF-A is decreased in ECs in PNET from imatinib-treated RIP1-Tag2 mice compared with controls, as assessed by quantitative RT-PCR. ***P < .001 vs control, Student t test. (C) Expression of VEGF-A is increased in ECs in B16/PDGFB tumors compared with B16/mock, as assessed by quantitative RT-PCR. **P < .01 vs B16/mock, Student t test. (D) Treatment of MS1 pancreatic islet ECs with 3μM imatinib did not alter the expression of VEGF-A or Bcl-w, as assessed by quantitative RT-PCR.