Figure 1.

(A) Microglial cells are derived from the embryonic yolk sac from myeloid progenitors that are generated prior to the initiation of hematopoiesis in the fetal liver. These progenitors migrate to the developing brain, colonize and differentiate into microglia, which is a long-lived self-sustaining population of the cells in the brain throughout life. (B). There is a sex bias in the number of microglia in the developing rodent brain, with males having more than females across the neonatal period. It is currently unknown whether more microglia progenitors are recruited into the male brain early in life, whether more proliferation occurs, or whether more cells survive in males than females (or some combination thereof).