Retinal Degeneration 12 (rd12): A new, spontaneously arisingmouse model for human Leber congenital amaurosis (LCA)

摘要

Purpose: To report the phenotype and characterization of a new,naturally occurring mouse model of hereditary retinal degeneration(rd12).Methods: The retinal phenotype of rd12 mice were studied usingserial indirect ophthalmoscopy, fundus photography, electroretinography(ERG), genetic analysis including linkage studies and geneidentification, immunohistochemistry, and biochemical analysis.Results: Mice homozygous for the rd12 mutation showed smallpunctate white spots on fundus examination at 5 months of age. Theretina in the rd12 homozygote had a normal appearance at the lightmicroscopic level until 6 weeks of age when occasional voids appeared inthe outer segments (OS) of the photoreceptor (PR) cells. The outernuclear layer (ONL) appeared normal until 3 months of age though moreobvious voids were detected in the OS. By 7 months of age, 6 to 8 layersof ONL remained in the mutant retina, and the OS were obviously shorter.The first sign of retinal degeneration was detected at the electronmicroscopic level around 3 weeks of age when occasional small lipid-likedroplets were detected in the retinal pigment epithelium (RPE). By 3months of age, much larger, lipid-like droplets accumulated in RPE cellsaccompanied by some OS degeneration. While the histology indicated arelatively slow retinal degeneration in the rd12 homozygous mutantmice, the rod ERG response was profoundly diminished even at 3 weeks ofage. Genetic analysis showed that rd12 was an autosomal recessivemutation and mapped to mouse chromosome 3 closely linked to D3Mit19,a location known to be near the mouse Rpe65 gene. Sequence analysisshowed that the mouse retinal degeneration is caused by a nonsensemutation in exon 3 of the Rpe65 gene, and the gene symbol for therd12 mutation has been updated to Rpe65rd12 to reflectthis. No RPE65 expression, 11-cis retinal, or rhodopsin could bedetected in retinas from rd12 homozygotes, while retinyl esters werefound to accumulate in the retinal pigment epithelium (RPE).Conclusions: Mutations in the retinal pigment epithelium geneencoding RPE65 cause an early onset autosomal recessive form of humanretinitis pigmentosa, known as Leber congenital amaurosis (LCA), whichresults in blindness or severely impaired vision in children. Anaturally arising mouse Rpe65 mutation provides a good model forstudying the pathology of human RPE65 mutations and the effects ofretinyl ester accumulation.