Fig. 1

Schematic of microglia development in mouse retina. a. Timeline of microglia entry to the retina. Microglia are derived from primitive yolk sac progenitors and are thought to enter the CNS via the circulatory system. Microglia have been documented in the developing murine retina at E11.5 but may be present earlier. Two waves of retinal microglia infiltration have been proposed. The first wave occurs embryonically and may involve microglia entry through the vitreal retina surface or migration from the ciliary region. A second wave may involve microglia infiltration from the optic disc or via blood vessels. b. Schematic of the adult retina. Rod (cyan) and cone (light purple) photoreceptors reside in the outer nuclear layer (ONL) and form connections with interneurons in the outer plexiform layer (OPL). Light induced signals are then relayed to neurons in the inner nuclear layer (INL), which is comprised of horizontal cells (dark blue), Müller glia (yellow), cone and rod bipolar cells (light and dark green), and amacrines (brown). Retinal ganglion cells (magenta) receive this information through synapses in the inner plexiform layer (IPL). Their somas reside in the ganglion cell layer (GCL) along with displaced amacrine cells (not pictured). Microglia cell are found predominately in the inner retina and are largely restricted to the synaptic layers