Figure 1.

Overview of microglia during brain development. (A) illustrates the developmental time points when microglia colonize and proliferate in the developing brain, beginning on embryonic day (E) 8.5. Microglia numbers peak in the rodent brain at postnatal day (P) 14 following local proliferation. Microglia then either die back or migrate from region to region until adult numbers are reached by P28. (B) indicates the different phenotypes of microglia across development based on unique gene expression patterns, listed in parentheses, and somewhat distinct morphologies. The brackets refer back to the developmental timeline depicted above in (A). (C) summarizes our current state of knowledge regarding which processes of development microglia have been shown to regulate, as well as the molecular factors involved. The brackets refer back to the developmental timeline depicted above in (A), illustrating when research to date has shown that microglia are involved in a given process. These data do not preclude the (likely) possibility that microglia regulate each developmental process beyond the time window indicated, but represent our current state of knowledge. Table 1 lists the publications that were used to design (C).