Fig. 1

Overview of microglial ontogeny in mice and zebrafish. a Microglia in mice derive from the immature erythromyeloid progenitors (EMPs) outside the central nervous system in the yolk sac during around embryonic day 8.0. During development, EMPs can enter the embryonic brain and take up residence, which is regulated by factors Pu.1, IRF8 and Runx1. During further development, IL-34 and CSF-1 are needed to promote microglia proliferation. Microglia can be constantly self-renewed throughout adult life. However, whether there are potential hidden progenitors besides the yolk sac have not been identified as yet. Potential non-yolk sac sources may also give arise to microglia in mice. b Two different origins of microglia can be found in zebrafish. Specifically, embryonic microglia arise from rostral blood islands in zebrafish, while adult microglia originate from ventral walls of dorsal aorta instead.