Expression intensity profiles of Aqp4, PDGFRα, and CD31 along cross sections of blood vessels in P9 corpus callosum of APCfl/fl control (a, b) and Olig2-cre: APCfl/fl (c, d) mice. Fluorescence intensities were measured using ZEN software. Yellow lines in each image indicate the cross section lines through vasculature along which intensities were measured. In the Olig2 cre:APCfl/fl mouse brain (c, d), Aqp4 intensity levels are reduced on vasculature when PDGFRα positive OPCs are clustered on blood vessels. (Graph Y axis= Fluorescence intensities; X axis= distance along vessel cross section in pixels). (e) Quantification of loss of AQP4+ astrocytic endfeet on blood vessels in P9 SC Olig2-cre:APCfl/fl compared to controls (n=6; APCfl/fl vs. Olig2-cre:APCfl/fl ****p = 1.47 E-6). Data were analyzed by unpaired two-sided Student’s t test. (f) Quantification of percentage of blood vessels with evidence of OPC clusters in P9 SC Olig2-cre:APCfl/fl compared to controls (n=6 animals; APCfl/fl vs. Olig2-cre:APCfl/fl ****p = 9.11 E-8). Data were analyzed by unpaired two-sided Student’s t test. Scale bars, 10 μm (a). **** P < 0.0001. Values are mean ± s.d. For all staining results, experiments were repeated at least three times independently with similar results.