Development of an Improved Method for Genetic Fate Mapping of Brain Microglia

As the resident macrophage cells of the brain, microglia are crucial for the phagocytosis of infectious agents, apoptotic cells and synapses. Developmentally, microglia originate from the embryonic yolk sac and serve important roles in the sculpting of neonatal neural circuits. In the context of severe brain injury or infection, bone‐marrow derived macrophages invade neural tissue, making it difficult to distinguish between invading macrophages and resident microglia. Although bone‐marrow derived macrophages can adopt some features of endogenous microglia, they are not able to fully recapitulate all of their properties, suggesting that there may be important functional differences between these two populations of cells. To distinguish between resident microglia and circulating myelogenous macrophages, we generated a P2ry12‐CreER mouse line. P2RY12 is a microglial‐specific nucleotide sensing GPCR that is important for microglial response to tissue damage. The P2ry12‐CreER line was generated by CRISPR‐facilitated homologous recombination and insertion of a 2A‐CreER sequence into the 3’ end of the P2RY12 coding sequence. Using immunofluorescent labeling and flow cytometry, we determined whether this recombination was specific to parenchymal microglia, as compared to meningeal, choroid plexus or perivascular macrophages. We also describe preliminary experiments that involve transcriptional profiling of P2ry12‐CreER recombined cells, using a Cre‐dependent Rpl22‐HA mouse line. Finally, using mouse models of neonatal and adult stroke, we used the P2ry12‐CreER line to fate map true brain microglia in the context of brain injury. Altogether, these results demonstrate the utility of this novel mouse line for genetic recombination, gene expression and fate‐mapping studies of brain microglia. Support or Funding Information NIH K08NS096192 This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .