(A) Representative TEM photomicrographs of P30 RPE from a WT retina (left panel) (n = 3). Carpet-like microvilli formed clusters or single villi oriented toward and between ROS at the apical RPE (right top panel). Infoldings of the basal membrane can be seen in the (left bottom panel). (B) Representative TEM photomicrographs of P30 RPE from an rd1 mouse injected at P1 with AAV-hRedO-H2b-GFP (n = 4). Degenerative changes in the RPE can be seen, including vacuolization in the cytoplasm in the apical region (left top panel, black asterisks), a reduced number of shortened infoldings (black arrowheads) and mitochondria in the basal region (bottom panel), and areas containing cellular debris and dead RPE cells (right top panel, white asterisks). (C) Representative TEM photomicrographs of P30 RPE from an rd1 mouse injected at P1 with AAV-Best1-Nrf2 and AAV-hRedO-H2b-GFP (n = 3). Microvilli appeared to form a compact barrier between the RPE and inner retina (left and right panel). The basal infolding region had parallel and long microvilli surrounded by mitochondria (middle bottom panel). (D) Representative TEM photomicrographs of P60 RPE from an rd1 mouse injected at P1 with AAV-Best1-Nrf2 and AAV-hRedO-H2b-GFP (n = 3). (E) Representative TEM photomicrographs of P60 RPE from an rd1 mouse injected at P1 with AAV-hRedO-H2b-GFP shows RPE death and cellular debris (black asterisks) (n = 3). BI, basal infoldings; M, microvilli; Mt, mitochondria; N, nucleus; ROS, rod outer segment. Scale bars: 2 μm.