title: Cone outer segment morphology and cone function in the Rpe65-/- Nrl-/- mouse retina are amenable to retinoid replacement.
abstract: OBJECTIVE
  RPE65, a major retinal pigment epithelium protein, is essential in generating 11-cis retinal, the chromophore for all opsins. Without chromophore, cone opsins are mislocalized and cones degenerate rapidly (e.g., Rpe65(-/-) mouse). Function, survival, and correct targeting of opsins is increased in Rpe65(-/-) cones on supplying 11-cis retinal. Here, we determine the consequences of 11-cis retinal withdrawal and supplementation on cone development in the all-cone Nrl(-/-) retina.
  
  
  METHODS
  Rpe65(-/-) Nrl(-/-), Nrl(-/-), and wild-type mice were examined. Cone structure was analyzed by using TUNEL assay, electron microscopy, and cone-specific antibodies. Cone function was assessed with light-adapted single-flash ERGs.
  
  
  RESULTS
  Rpe65(-/-)Nrl(-/-) mice had an increased number of TUNEL-positive photoreceptors during programmed cell death compared with Nrl(-/-) mice, in addition to accelerated age-related degeneration. Cone function in Rpe65(-/-)Nrl(-/-) mice was minimal, and opsins were mislocalized. Treatment with 11-cis retinal restored cone function, promoted outer segment formation, and enabled opsin trafficking to outer segments. Eliminating Rpe65 prevented rosette formation in Nrl(-/-) retinas; supplementation of Rpe65(-/-)Nrl(-/-) mice with 11-cis retinal resulted in their reoccurrence.
  
  
  CONCLUSIONS
  Taken together, function and opsin trafficking in Nrl(-/-) and wild-type cones are comparable, confirming and extending our findings that cone maturation and outer segment development are dependent on the presence of chromophore. The data on age-related cone death in Rpe65(-/-)Nrl(-/-) mice and the reintroduction of rosettes after 11-cis retinal injections confirm that outer segments, which for steric reasons appear to introduce rosettes in an all-cone retina, are essential for cell survival. These results are important for understanding and treating chromophore-related cone dystrophies.
authors.affiliation: Department of Neurosciences, Division of Research, Medical University of South Carolina, Charleston, South Carolina 29425, USA.
authors.forename: Kannan
authors.initials: K
authors.lastname: Kunchithapautham
authors.forename: Beth
authors.initials: B
authors.lastname: Coughlin
authors.forename: Rosalie K
authors.initials: RK
authors.lastname: Crouch
authors.forename: Bärbel
authors.initials: B
authors.lastname: Rohrer
mesh_terms: D000818:Animals; D017209:Apoptosis; D050976:Basic-Leucine Zipper Transcription Factors / Q000502:physiology*; D002352:Carrier Proteins / Q000502:physiology*; D004596:Electroretinography; D005136:Eye Proteins / Q000502:physiology*; D019084:Fluorescent Antibody Technique, Indirect; D020287:In Situ Nick-End Labeling; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D055355:Opsins / Q000378:metabolism; D010775:Photic Stimulation; D017949:Retinal Cone Photoreceptor Cells / Q000473:pathology* / Q000502:physiology*; D012162:Retinal Degeneration / Q000378:metabolism / Q000503:physiopathology*; D012172:Retinaldehyde / Q000008:administration & dosage / Q000502:physiology*; D019745:cis-trans-Isomerases; D000099178:Retinoid Isomerohydrolase
chemical_list: D050976:Basic-Leucine Zipper Transcription Factors; D002352:Carrier Proteins; D005136:Eye Proteins; D055355:Opsins; D012172:Retinaldehyde; D019745:cis-trans-Isomerases; D000099178:Retinoid Isomerohydrolase; C084884:Nrl protein, mouse