Isorhodopsin rather than rhodopsin mediates rod function in RPE65 knock-out mice.
The chromophore of visual pigments is 11-cis-retinal and, thus, in its absence, opsin is not photosensitive and no visual function exists. However, in the RPE65 knockout (Rpe65-/-) mouse, where synthesis of 11-cis-retinal does not occur, a minimal visual response from rod photoreceptors is obtained. We have examined if an alternative pathway exists for cis-retinoid generation in the absence of RPE65. Cyclic-light-reared, 2-month-old Rpe65-/- mice were placed in complete darkness. No exogenous retinoids were administered. After 4 weeks, enhanced a- and b-wave amplitudes were obtained, increasing >10-fold for the a-wave and >3-fold for the b-wave as compared with cyclic-light-reared Rpe65-/- mice. Visual-pigment levels increased to approximately 10 pmol per retina, compared with no measurable pigment for cyclic-light-reared Rpe65-/- mice. The lambdamax of the isolated pigment was 487 nm, characteristic for isorhodopsin. Retinoid extractions confirmed the presence of 9-cis-retinal and the absence of 11-cis-retinal. Once the Rpe65-/- mice were returned to cyclic light, within 48 h the electroretinogram function returned to levels found in Rpe65-/- mice maintained in cyclic light. This dark-mediated pathway is also operational in older animals, because 13-month-old Rpe65-/- mice kept in prolonged darkness (12 weeks) had increased isorhodopsin levels and electroretinogram a- and b-wave amplitudes. These studies demonstrate that a pathway exists in the eye for the generation of 9-cis-retinal that is independent of RPE65 and light.
Department of Ophthalmology, Medical University of South Carolina, 167 Ashley Avenue, Charleston, SC 29425, USA.
Jie
J
Fan
Baerbel
B
Rohrer
Gennadiy
G
Moiseyev
Jian-Xing
JX
Ma
Rosalie K
RK
Crouch
D000818:Animals; D002352:Carrier Proteins; D002851:Chromatography, High Pressure Liquid; D004224:Diterpenes; D004596:Electroretinography; D005136:Eye Proteins; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D008956:Models, Chemical; D010857:Pigment Epithelium of Eye / Q000378:metabolism; D010860:Pigments, Biological / Q000378:metabolism; D011506:Proteins / Q000235:genetics* / Q000502:physiology; D012160:Retina / Q000378:metabolism; D012168:Retinal Pigments / Q000378:metabolism; D012172:Retinaldehyde / Q000378:metabolism; D012176:Retinoids / Q000378:metabolism; D012243:Rhodopsin / Q000502:physiology*; D013997:Time Factors; D019745:cis-trans-Isomerases; D000099178:Retinoid Isomerohydrolase
D002352:Carrier Proteins; D004224:Diterpenes; D005136:Eye Proteins; D010860:Pigments, Biological; D011506:Proteins; D012168:Retinal Pigments; D012172:Retinaldehyde; D012176:Retinoids; D012243:Rhodopsin; D019745:cis-trans-Isomerases; D000099178:Retinoid Isomerohydrolase; C042882:isorhodopsin; C031390:9-cis-retinal