Spatio-temporal dynamics of macroglial cell organisation and proximity to blood vessels during postnatal development

Brain cortical development results from the proliferation, differentiation, migration and maturation of many cell types. While neuronal development is well characterized, the mechanisms regulating macroglial cells (oligodendrocytes and astrocytes) development remain largely unknown. Recent works suggest that the vascular system plays a key, yet under-evaluated role in this process. To investigate this, we developed VeCell , a Fiji plugin designed to analyse the spatial organization of macroglial cells relative to blood vessels. Using immunolabeling for Sry-box transcription factor (Sox) 9 (macroglial progenitors and astrocytes) and Sox10 (oligodendrocyte lineage), we determined macroglia density, distribution and proximity to blood vessels from postnatal day (P) 1 to P60 in the somatosensory cortex. We showed that Sox9+ cells were evenly distributed across cortical layers with regular intercellular spacing. In contrast, Sox10+ cells concentrated in deeper cortical layers, and exhibited a random distribution. Vascular density and branching increased markedly between P5 and P15 and macroglial cells were closer to blood vessels from P15 onward. As a proof of concept, we used Vecell to show that astrocyte cortical distribution is preserved in MLC1-deficient mice, a model of Megalencephalic leukoencephalopathy with subcortical cysts, in which astrocyte perivascular coverage is altered. Thus, VeCell is a powerful tool to characterize and quantify macroglial cell distribution in the brain and in relation to the vasculature. It revealed distinct distribution and postnatal development patterns for astrocytes and oligodendrocytes.