Differences in RDS trafficking, assembly and function in cones versus rods: insights from studies of C150S-RDS.

Cysteine 150 of retinal degeneration slow protein (RDS) mediates the intermolecular disulfide bonding necessary for large RDS complex assembly and morphogenesis of the rim region of photoreceptor outer segments. Previously, we showed that cones have a different requirement for RDS than rods, but the nature of that difference was unclear. Here, we express oligomerization-incompetent RDS (C150S-RDS) in the cone-dominant nrl(-/-) mouse. Expression of C150S-RDS leads to dominant functional abnormalities, ultrastructural changes, biochemical anomalies and protein mislocalization in cones. These data suggest that RDS complexes in cones are more susceptible to disruption than those in rods, possibly due to structural or microenvironmental differences in the two cell types. Furthermore, our results suggest that RDS intermolecular disulfide bonding may be part of RDS inner-segment assembly in cones but not in rods. These data highlight significant differences in assembly, trafficking and function of RDS in rods versus cones.