title: Nrl-knockout mice deficient in Rpe65 fail to synthesize 11-cis retinal and cone outer segments.
abstract: OBJECTIVE
  To define rod and cone function further in terms of visual cycle mechanism, the retinal phenotype resulting from Rpe65 (retinoid isomerase I) deficiency in Nrl(-)(/)(-) mice having a single class of photoreceptors resembling wild-type cones was characterized and outcomes of retinoid supplementation evaluated.
  
  
  METHODS
  Rpe65(-)(/)(-)/Nrl(-)(/)(-) mice were generated by breeding Rpe65(-)(/)(-) and Nrl(-)(/)(-) strains. Retinal histology, protein expression, retinoid content, and electroretinographic (ERG) responses were evaluated before and after treatment with 11-cis retinal by intraperitoneal injection. Results Retinas of young Rpe65(-)(/-)/Nrl(-)(/-) mice exhibited normal lamination, but lacked intact photoreceptor outer segments at all ages examined. Rpe65, Nrl, and rhodopsin were not detected, and S-opsin and M/L-opsin levels were reduced. Retinyl esters were the only retinoids present. In contrast, Nrl(-)(/)(-) mice exhibited decreased levels of retinaldehydes and retinyl esters, and elevated levels of retinols. ERG responses were elicited from Rpe65(-)(/-)/Nrl(-)(/-) mice only at the two highest intensities over a 4-log-unit range. Significant retinal thinning and outer nuclear layer loss occurred in Rpe65(-)(/-)/Nrl(-)(/-) mice with aging. Administration of exogenous 11-cis retinal did not rescue retinal morphology or markedly improve ERG responses.
  
  
  CONCLUSIONS
  The findings provide clarification of reported cone loss of function in Rpe65(-)(/-)/Nrl(-)(/-) mice, now showing that chromophore absence results in destabilized cone outer segments and rapid retinal degeneration. The data support the view that rod-dominant retinas do not have a cone-specific mechanism for 11-cis retinal synthesis and have potential significance for therapeutic strategies for rescue of cone-rich retinal regions affected by disease in the aging human population.
authors.affiliation: Department of Ophthalmology and Visual Sciences, University of Michigan Medical School, Ann Arbor, Michigan 48105, USA.
authors.forename: Kecia L
authors.initials: KL
authors.lastname: Feathers
authors.forename: Arkady L
authors.initials: AL
authors.lastname: Lyubarsky
authors.forename: Naheed W
authors.initials: NW
authors.lastname: Khan
authors.forename: Karen
authors.initials: K
authors.lastname: Teofilo
authors.forename: Anand
authors.initials: A
authors.lastname: Swaroop
authors.forename: David S
authors.initials: DS
authors.lastname: Williams
authors.forename: Edward N
authors.initials: EN
authors.lastname: Pugh
authors.forename: Debra A
authors.initials: DA
authors.lastname: Thompson
mesh_terms: D000818:Animals; D050976:Basic-Leucine Zipper Transcription Factors / Q000502:physiology*; D015153:Blotting, Western; D002352:Carrier Proteins / Q000502:physiology*; D002851:Chromatography, High Pressure Liquid; D003623:Dark Adaptation; D004596:Electroretinography; D005136:Eye Proteins / Q000502:physiology*; D005260:Female; D019084:Fluorescent Antibody Technique, Indirect; D005838:Genotype; D007274:Injections, Intraperitoneal; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D046529:Microscopy, Electron, Transmission; D017949:Retinal Cone Photoreceptor Cells / Q000378:metabolism / Q000503:physiopathology / Q000648:ultrastructure*; D012162:Retinal Degeneration / Q000188:drug therapy / Q000378:metabolism* / Q000503:physiopathology; D012172:Retinaldehyde / Q000008:administration & dosage / Q000096:biosynthesis*; D012176:Retinoids / Q000378:metabolism; D017299:Rod Opsins / Q000378:metabolism; D019745:cis-trans-Isomerases; D000099178:Retinoid Isomerohydrolase
chemical_list: D050976:Basic-Leucine Zipper Transcription Factors; D002352:Carrier Proteins; D005136:Eye Proteins; D012172:Retinaldehyde; D012176:Retinoids; D017299:Rod Opsins; D019745:cis-trans-Isomerases; D000099178:Retinoid Isomerohydrolase; C084884:Nrl protein, mouse