CD206+macrophages transventricularly infiltrate the early embryonic cerebral wall to differentiate into microglia

The relationships between tissue-resident microglia and early macrophages, especially their lineage segre-gation outside the yolk sac, have been recently explored, providing a model in which a conversion from macrophages seeds microglia during brain development. However, spatiotemporal evidence to support such microglial seeding in situ and to explain how it occurs has not been obtained. By cell tracking via slice culture, intravital imaging, and Flash tag-mediated or genetic labeling, we find that intraventricular CD206+ macrophages, which are abundantly observed along the inner surface of the mouse cerebral wall, frequently enter the pallium at embryonic day 12. Immunofluorescence of the tracked cells show that postinfiltrative macrophages in the pallium acquire microglial properties while losing the CD206+ macrophage phenotype. We also find that intraventricular macrophages are supplied transepithelially from the roof plate. This study demonstrates that the roof plate->ventricle->palliumroute is an essential path for microglial colonization into the embryonic mouse brain.

Automated summary

By tracking cells, researchers found that CD206+ macrophages frequently enter the inner surface of the mouse cerebral wall and convert into microglia at embryonic day 12. It was also discovered that intraventricular macrophages are supplied transepithelially from the roof plate. This study demonstrates that the roof plate->ventricle->pallium route is essential for microglial colonization into the embryonic mouse brain.