One of the characteristics of microglia in vivo is their ability to survey the parenchyma from their static tiling positions, yet revert to an amoeboid and actively migrating state in response to injury. Migration towards a site of cellular damage is driven by purinergic receptors such as P2RY12/13, in response to ATP/ADP release from dying cells. We took advantage of our 3D culture system to model such localized damage and observe microglial behavior in real-time. Figure 6h and Supplementary Movies 8, 9 display the time-lapse reaction of embedded GFP+ microglia to a focal laser injury (yellow arrowhead at 5′). Microglia reacted within minutes by extending a single long process towards the injury center, making contact with the damaged zone (t =20′). They then rapidly migrated their cell body to surround the damaged area. In contrast, microglia away from the injury site stayed in place.
