Figure 4. Cngb1^–/– dogs have a progressive retinal thinning with preservation of the REC⁺ in the area centralis.

(A) Measurement of REC⁺, ONL, and inner segment/outer segment (IS/OS) layer thickness by SD-OCT cross-sectional images in a vertical plane through the area centralis, measured every 0.5 mm. The negative numbers are inferior to the area centralis. Control dogs: n = 3; Cngb1^–/– affected dogs: n = 3 dogs 6–7 months of age; n = 3 dogs 18–19 months of age; n = 1 dog 48 months of age; n = 2 dogs 66–69 months of age. (B) Heatmaps demonstrating preservation of photoreceptor thickness in the area centralis and horizontally along the visual streak. REC⁺ thickness in Cngb1^–/– dogs of different ages compared with a control (WT) dog. n = 3 control dogs; n = 3 Cngb1^–/– dogs at 18 months of age; n = 1 Cngb1^–/– dog at 48 months of age; and n = 2 Cngb1^–/– dogs at 66 months of age. (C) Representative images of plastic-embedded semi-thin retinal samples from an 8-week-old control dog compared with samples from a Cngb1^–/– dog. The inner segments of cones are located adjacent to the inner segments of rods in the control dog. Shortening of the rod inner segments in the Cngb1^–/– dogs resulted in cone inner segments extending to the level of the rod outer segments. Rod outer segments appeared disorganized and deteriorated over the first 28 months. Initially, cone inner segments appeared grossly normal and then, with rod loss, initially appeared widened (at 12 months) but then became shortened and atrophied (at 28 months). Sections (500-nm) were stained with epoxy tissue stain. Arrows indicate the cone inner segment. Scale bar: 20 μm. n = 4 control dogs; n = 1 Cngb1^–/– dog at 2, 5, 12, and 28 months of age; n = 2 Cngb1^–/– dogs at 18 months of age. (D) Representative images of IHC with hCAR (labels the entire length of the cones) show well-preserved cone morphology in the younger animals. In the older Cngb1^–/– affected dogs (18 and 30 months of age), the cones were still visible, albeit shortened. Scale bar: 20 μm. n = 2 control dogs; n = 2 Cngb1^–/– dogs at 2 and 18 months of age; n = 1 Cngb1^–/– dog at 12 and 30 months of age. (E) Representative transmission electron microscopic images of rods (R) and cones (C) show a reasonably normal arrangement of rod discs at 2 months of age in the Cngb1^–/– dog, but by 12 months of age, the rod outer segments had deteriorated, but the cone outer segments appeared relatively normal. Scale bar: 2 μm. n = 4 controls; n = 1 Cngb1^–/– dog at 2 and 12 months of age.