For expression studies, mice were humanely killed 2 weeks after the viral injections (n = 5), and the eyes were removed and fixed with 4% paraformaldehyde in phosphate-buffered saline solution (PBS) for 1 hour. The eyes were then transferred to 0.4% paraformaldehyde overnight. To make flat mounts, the cornea and crystalline lens were removed, and the entire retina was carefully dissected from the eye cup. Four radial cuts were made from the edge to the equator of the retina to make it flat. After three washes in PBS, retinas were permeabilized with 0.5% Triton X-100 (Dow Chemical Corporation, Midland, MI, USA) in PBS for 1 hour followed by incubation with a blocking solution of 0.5% Triton X-100 and 10% goat serum for 1 hour. The flat-mounted retinas were then rinsed in PBS and incubated with a mixture of either mouse monoclonal anti-human ND4 antibody (Abnova, Taipei City, Taiwan) or mouse monoclonal anti-FLAG antibody (Sigma-Aldrich Corp., St. Louis, MO, USA), monoclonal rat Thy1.2 antibody (1:200; Abcam, Cambridge, MA, USA), or polyclonal rabbit anti-porin antibody (1:500; Abcam) overnight at 4°C. Primary antibody solution is contained in 10% goat serum and 0.2% Triton X-100 in PBS (pH, 7.4). After three washes with PBS, retinas were reacted with the secondary antibody, goat anti-mouse Cy3 (Jackson Immunoresearch Laboratories, Inc., West Grove, PA, USA), goat anti-mouse FITC (Jackson Immunoresearch Laboratories, Inc.), goat anti-rat Cy2 (Jackson Immunoresearch Laboratories, Inc.), or goat anti-rabbit Cy5 (Jackson Immunoresearch Laboratories, Inc.), and 4′,6-diamidino-2-phenylindole (DAPI; 2 μg/mL) (Santa Cruz Biotechnology, Inc., Santa Cruz, CA, USA) in 1:500 dilution contained in 10% goat serum and 0.2% Triton X-100 and incubated at 4°C overnight. Retinal tissues were finally washed three times in PBS. Whole mounts were then placed on glass slides (RGC layer facing up), cover slipped, and observed for fluorescence with a confocal microscope (TCS SP5; Leica, Wetzlar, Germany). For cryosections, the retinas were incubated overnight in 30% sucrose and then embedded in optimal cutting temperature embedding compound (Sakura Finetek, Torrance, CA, USA). Retinal sections, 8 μm in thickness, were then mounted with fluorescent mounting medium (Vectashield; Vector Laboratories, Burlingame, CA, USA) and examined for fluorescence by confocal microscopy.