OPCs perivascular clusters resolve over time with reinvestment of astrocyte endfeet on blood vessels and reduction in microglial activation. (a) Use of Olig2-cre:APCfl/fl:TdTomato mice, to label OPC perivascular clusters in red (arrows), shows a decrease in cluster size around CD31+ vessels in corpus callosum through postnatal times P9, P12, P16 and P30. (b) Use of Olig2-cre:APCfl/fl:Aldh1l1-GFP at P9, P12, P16 and P30 in the corpus callosum shows a reduction in perivascular clusters over time (labelled with dapi, arrows) and reinvestment of GFP-labelled astrocyte endfeet on CD31+ vasculature. (c) Quantification of OPC cluster frequencies during development in Olig2-cre:APCfl/fl mouse CC at P9, P12, P16, P20 and P30 (n=6 animals at each time point; all statistical analyses compared to P9, P12 vs. P9 ns p = 0.1948, P16 vs. P9 * p = 0.141, P20 vs. P9 **** p = 2.25 E-5, P30 vs. P9 **** p = 2.19 E-6). Data were analyzed by unpaired two-sided Student’s t test. (d) Use of Olig2-cre:APCfl/fl corpus callosum at P9, P12, P16 and P30 shows a reduction in activated microglia (labelled with F4/80) over time around perivascular clusters (labelled with dapi). Scale bars, 80 μm (a, d), 30 μm (b). * P < 0.05, **** P < 0.0001. Values are mean ± s.d. For all staining results, experiments were repeated at least three times independently with similar results.