Fig. 1

Timecourse of microglia activation and photoreceptor clearance. a IHC of retinal sections of dark-reared (0 h) and light-exposed Arr1^−/− mice (24–240 h). Light induced widespread migration of Iba1⁺ cells (green) into the outer retina. By 72 h, the outer retina (OS, IS, ONL) was markedly thinned and by 240 h had nearly vanished. b–d Quantification of Iba1⁺ cells in IHC sections. b The number of Iba1⁺ cells in the ONL per 100 μm increased significantly in two phases after light onset in Arr1^−/− but did not change in dark-reared wild type (WT) controls. c The percent of Iba1⁺ cells actively engulfing photoreceptors increased significantly at 36 h in Arr1^−/− and remained elevated through 96 h; there was no change in WT. Data in B and C re-analyzed from Levine et al., 2014. d In Arr1^−/− mice, the majority of Iba1⁺ cells in dark-reared animals (0 h) were located in the plexiform layers, but after 72–96 h of light exposure, Iba1⁺ cells were also observed in the vitreous, RGC, ONL, and subretinal layers. Note that the discrepancy in quantification between 1B and 1D is due to the inclusion of subretinal and vitreal Iba1⁺ cells in 1D, which were not counted in the first study. Vitreal Cd11b⁺ cells may include a population of hyalocytes. Scale bar is 50 μm in A. OS photoreceptor outer segment layer, IS photoreceptor inner segment layer, ONL outer nuclear layer, OPL outer plexiform layer, INL inner nuclear layer, IPL inner plexiform layer, RGC retinal ganglion cell layer. *p < 0.05, **p < 0.01, ***p < 0.001; error bars are SEM, n = 7–18 locations per time point (locations selected from 3 to 9 sections across 2–3 mice per strain per time)