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Rosalie K. Crouch, Jian-Xing Ma, Peter H. Tang; Rpe65 Is Present Within The Inner Segments Of Cones In The Cone-dominant Retina, Suggesting Its Role In The Cone Visual Cycle. Invest. Ophthalmol. Vis. Sci. 2011;52(14):3646. doi: https://doi.org/.
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While previous studies have suggested that RPE65, the retinoid isomerase of the classic visual cycle, is present within the outer segment of cones in the rod-dominant retina, little is known about its localization within cones of the cone-dominant retina. In the present study, we evaluate the presence of RPE65 within cones of the cone-dominant chicken (Gallus gallus) and pure-cone lizard (Anolis carolinensis) retinas, and compare against the neural retinal leucine zipper knockout (Nrl-/-) mouse, a rod-dominant species genetically modified to express a pure-cone retina.
Antibodies targeting residues 150-164 (PETLET) or 473-486 (DALEED) of bovine RPE65 were utilized. Immunoblots were performed to verify antibody specificity. Immunohistochemistry techniques were utilized to visualize RPE65 protein within the eyecup.
PETLET and DALEED antibodies detected a ~61 KD major band in immunoblots, corresponding to the known size of RPE65, and detection was blocked by incubating with epitope peptides. Both antibodies showed similar RPE65 staining within the inner segment regions of chicken and lizard cones. Further studies within these cones suggest RPE65 is localized within the paraboloid, a glycogen-storage region of the inner segment composed of ER and Golgi. Interestingly, in Nrl-/- mouse cones, RPE65 is detected within the outer segment in a pattern similar to cones of wildtype mice.
The role of RPE65 in cones is unclear, although our studies have shown that cones in mouse strains lacking RPE65 are modestly chromophore deprived. Those results and this finding that RPE65 is in the inner segment of the cone-dominant retina suggest a role for RPE65 in the cone-specific visual cycle.
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