Figure 13.

Diagram of primordial rod disc reorientation. In Rho^+/+ mice with normal copies of WT rhodopsin (Rho^+/+), sagittally oriented primordial discs (purple) were observed only in young rods. In adult rods, all disc membranes were oriented transversely (blue). These observations indicate that primordial discs shift from a sagittal to a transverse orientation. In Rho^P23H/+ mice that express both WT opsin and P23H opsin, sagittally oriented primordial disc membranes both enlarge (purple) and can retain their sagittal orientation as rods mature. These observations indicate that P23H opsin interferes with the process of disc membrane reorientation. That this is a dominant-negative effect is reinforced by the observation that primordial disc membranes containing only P23H opsin are incapable of orienting transversely (Rho^P23H/P23H, purple). Indeed, the combined evidence strongly indicates that primordial discs normally shift from a sagittal to transverse orientation in the rods of Rho^+/+ adult mice.