Targeted knockdown of Cerkl, a retinal dystrophy gene, causes mild affectation of the retinal ganglion cell layer.

In order to approach the function of the retinal dystrophy CERKL gene we generated a novel knockout mouse model by cre-mediated targeted deletion of the Cerkl first exon and proximal promoter. The excised genomic region (2.3kb) encompassed the first Cerkl exon, upstream sequences including the proximal promoter and the initial segment of the first intron. The Cerkl-/- mice were viable and fertile. The targeted Cerkl deletion resulted in a knockdown more than a knockout model, given that alternative promoters (unreported at that time) directed basal expression of Cerkl (35%). In situ hybridizations and immunohistochemistry showed that this remnant expression was moderate in the photoreceptors and weak in the ganglion and inner cell layers. Morphological characterization of the Cerkl-/- retinas did not show any gross structural changes, even at 12 months of age. However, some clear and consistent signals of gliosis and retinal stress were detected by the statistically significant increase of i) the glial fibrillary antigen protein (GFAP) expression, and ii) apoptosis, as detected by TUNEL. Remarkably, consistent non-progressive perturbation (from birth up to 12 months of age) of ganglion cells was supported by the decrease of the Brn3a marker expression as well as the reduced oscillatory potentials in the electroretinographic recordings. In conclusion, the Cerkl-/- knockdown shows a mild retinal phenotype, with increased levels of cellular stress and apoptosis indicators, and clear signs of functional alteration at the ganglion cell layer, but no detectable morphological changes.

Early onset retinal dystrophy due to mutations in LRAT: molecular analysis and detailed phenotypic study.

PURPOSE: To report novel variants and characterize the phenotype associated with the autosomal recessive retinal dystrophy caused by mutations in the lecithin retinol acyltransferase (LRAT) gene. METHODS: A total of 149 patients with Leber's congenital amaurosis (LCA) or early onset retinal dystrophy were screened for mutations in LCA-associated genes using an arrayed-primer extension (APEX) genotyping microarray (Asper Ophthalmics). LRAT sequencing was subsequently performed in this 148-patient panel. Patients identified with mutations underwent further detailed phenotyping. RESULTS: APEX analysis identified one patient with a previously reported homozygous LRAT mutation. Sequencing of the panel identified three additional patients with novel homozygous LRAT mutations in exon 2. All four patients had severe progressive nyctalopia, visual field constriction, and photophilia in childhood. Visual acuity ranged from 0.22 logMAR to hand motion. Funduscopy revealed severe retinal pigment epithelial atrophy and minimal retinal pigmentation. Asteroid hyalosis and macular epiretinal fibrosis were frequent. All demonstrated reduced fundus autofluorescence. Optical coherence tomography identified disrupted retinal lamination, outer-retinal debris, and an unidentifiable photoreceptor layer in two cases. Full-field electroretinograms were undetectable or showed severe rod-cone dysfunction. Photopic perimetry revealed severe visual field constriction. Dark-adapted perimetry demonstrated markedly reduced photoreceptor sensitivity. Dark-adapted spectral sensitivity measurements identified functioning rods in two of three patients. All three had severely reduced L- and M-cone sensitivity and poor color discrimination. CONCLUSIONS: LRAT mutations cause a severe, early childhood onset, progressive retinal dystrophy. Phenotypic similarities to the retinal dysfunction associated with RPE-specific protein 65 kDa mutations, another visual cycle gene, suggest that LRAT deficiency may show a good response to novel therapies.

Evidence for baseline retinal pigment epithelium pathology in the Trp1-Cre mouse.

The increasing popularity of the Cre/loxP recombination system has led to the generation of numerous transgenic mouse lines in which Cre recombinase is expressed under the control of organ- or cell-specific promoters. Alterations in retinal pigment epithelium (RPE), a multifunctional cell monolayer that separates the retinal photoreceptors from the choroid, are prevalent in the pathogenesis of a number of ocular disorders, including age-related macular degeneration. To date, six transgenic mouse lines have been developed that target Cre to the RPE under the control of various gene promoters. However, multiple lines of evidence indicate that high levels of Cre expression can be toxic to mammalian cells. In this study, we report that in the Trp1-Cre mouse, a commonly used transgenic Cre strain for RPE gene function studies, Cre recombinase expression alone leads to RPE dysfunction and concomitant disorganization of RPE layer morphology, large areas of RPE atrophy, retinal photoreceptor dysfunction, and microglial cell activation in the affected areas. The phenotype described herein is similar to previously published reports of conditional gene knockouts that used the Trp1-Cre mouse, suggesting that Cre toxicity alone could account for some of the reported phenotypes and highlighting the importance of the inclusion of Cre-expressing mice as controls in conditional gene targeting studies.

The Marshall M. Parks memorial lecture: making sense of early-onset childhood retinal dystrophies--the clinical phenotype of Leber congenital amaurosis.

A correct diagnosis of the early-onset childhood retinal dystrophies requires careful clinical evaluation, the detection of suggestive or pathognomonic ophthalmoscopic clues, the use of electrophysiology to document characteristic electroretinographic findings and, in some cases, the utilisation of newer diagnostic modalities such as optical coherence tomography. Molecular diagnosis confirms the clinical diagnosis and provides the basis for possible future gene therapy. A strict definition of early-onset childhood retinal dystrophies (EOCRDs) does not exist, but inherited retinal dystrophies that are diagnosed in the first few years of life could be included under this umbrella terminology. The clinical ophthalmological manifestations of these diseases may or may not be detected at birth, and include the triad of severe vision loss, sensory nystagmus and electroretinographic abnormalities. Their clinical manifestations are light sensitivity, night blindness, fundus pigmentary changes and other psychophysical and retinal anatomic abnormalities. Diseases that could be included in the EOCRDs are Leber congenital amaurosis, achromatopsia, congenital stationary night blindness, X-linked juvenile retinoschisis, Goldmann-Favre disease and other NR2E3-related disorders, and possibly some very early-onset forms of Stargardt disease and juvenile retinitis pigmentosa. In this paper, phenotypic clues to the diagnosis of the underlying molecular defect in patients with Leber congenital amaurosis are discussed and an overview of the clinical workup of the child with a retinal dystrophy is presented. An accurate diagnosis of individual EOCRD allows a better prediction of the clinical course and the planning of possible and emerging therapies.