Embryonic microglia maintain the brain's cortical fault lines

Lawrence et al. report that fetal cortical boundaries are susceptible to morphogenetic stress that regulates a microglia state resembling postnatal, axon-tract associated microglia (ATM). This state performs a newfound function at these boundaries by preventing the formation of cavitary lesions, mediated in part by Spp1-regulated phagocytosis of fibronectin 1.