Figure 3. Expression of photoreceptor promoter-driven fluorescent proteins in retinas transduced with mixtures of two lentiviruses. Lentiviral vectors carrying transgenes comprised of various photoreceptor promoters driving expression of GFP or tdTOM fluorescent proteins were mixed in equal volumes and injected into the developing neural tubes of chicken embryos (embryonic day 2 –E2) in ovo. The injected virus mixtures were as follows: A-E: pFIN-GCAP292-GFP (2.2×10¹⁰ vector genomes/µl) and pFIN-IRBP1783-tdTOM (1.6×10¹⁰ vector genomes/µl); F-J: pFIN-RK-GFP-WPRE (1.2×10¹⁰ vector genomes/µl) and pFIN-IRBP1783-tdTOM (1.6×10¹⁰ vector genomes/µl); K-O: pFIN-RK-GFP-WPRE (1.2×10¹⁰ vector genomes/µl) and pFIN-IRBP156-tdTOM (5.6×10¹⁰ vector genomes/µl); P-T: pFIN-GCAP292-GFP (2.2×10¹⁰ vector genomes/µl) and pFIN-XOPS-tdTOM (1.2×10⁹ vector genomes/µl). We have previously shown that the GCAP292 and IRBP1783 promoters are active in cone cells [18]. RK and IRBP156 are active in both rod and cone cells and XOPS is only active in rod cells (Figure 1). For each image series, the transduced retina was photographed from the photoreceptor side of the whole mount using GFP (A, F, K, P) and CHER (B, G, L, Q) filters. These images were then merged to identify cells expressing both reporter proteins (C, H, M, R). The merged images were analyzed using the co-localization module of the Zeiss AxioVision Image Suite. The results of these analyses are expressed as the percent of the transduced area in the image (pixels) containing co-localized GFP and tdTOM (yellow bar) or GFP (green bar) or tdTOM (red bar) fluorescence alone (D, I, N, S). The images shown in E, J, O, and T were extracted from the merged images shown in C, H, M, and R and show only those areas of the merged image in which GFP was co-localized with tdTOM. The scale bar shown in A is applicable to all images and equals 50 µm.