Close to 100 genes cause retinitis pigmentosa, a Mendelian rare disease that affects 1 out of 4000 people worldwide. Mutations in the ceramide kinase-like gene (CERKL) are a prevalent cause of autosomal recessive cause retinitis pigmentosa and cone-rod dystrophy, but the functional role of this gene in the retina has yet to be fully determined. We aimed to generate a mouse model that resembles the phenotypic traits of patients carrying CERKL mutations to undertake functional studies and assay therapeutic approaches. METHODS. The Cerkl locus has been deleted (around 97 kb of genomic DNA) by gene editing using the CRISPR-Cas9 D10A nickase. Because the deletion of the Cerkl locus is lethal in mice in homozygosis, a double heterozygote mouse model with less than 10% residual Cerkl expression has been generated. The phenotypic alterations of the retina of this new model have been characterized at the morphological and electrophysiological levels. RESULTS. This Cerkl KD/KO model shows retinal degeneration, with a decreased number of cones and progressive photoreceptor loss, poorly stacked photoreceptor outer segment membranes, defective retinal pigment epithelium phagocytosis, and altered electrophysiological recordings in aged retinas. CONCLUSIONS. To our knowledge, this is the first Cerkl mouse model to mimic many of the phenotypic traits, including the slow but progressive retinal degeneration, shown by human patients carrying CERKL mutations. This useful model will provide unprecedented insights into the retinal molecular pathways altered in these patients and will contribute to the design of effective treatments.

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Mutations in NR2E3 cause retinitis pigmentosa (RP) and enhanced S-cone syndrome (ESCS) in humans. This gene produces a large isoform encoded in 8 exons and a previously unreported shorter isoform of 7 exons, whose function is unknown. We generated two mouse models by targeting exon 8 of Nr2e3 using CRISPR/Cas9-D10A nickase. Allele D27 is an in-frame deletion of 27 bp that ablates the dimerization domain, whereas allele DE8 (full deletion of exon 8), produces only the short isoform that lacks the dimerization and repressor domains. The D27 mutant shows developmental alterations and a non-progressive electrophysiological dysfunction that resembles the ESCS phenotype. The DE8 mutant exhibits progressive retinal degeneration, as occurs in human RP patients. Interestingly, the mutant retinas show invaginations similar to fovea-like pits. Our mutants suggest a role of Nr2e3 as a conepatterning regulator and provide valuable models for studying mechanisms of NR2E3associated retinal dystrophies and evaluating potential therapies.

Purpose: To characterize a mouse model of complete blindness after induction of retinal degeneration based on the degenerative capacity of NaIO3 on cell photoreceptors, rods and cones, and to test the effect of new pharmacological tools. Methods: Two doses of NaIO3 (40 mg/kg and 60 mg/kg) were intraperitoneally injected into a series of C57BL/6J mice with a mutation in the Opn4−/− gene. The effect of NaIO3 on the retina was assessed at 7, 14, 21 and 28 days after the injection by means of visual behavioural test, electroretinogram (ERG) recordings and immunohistochemical staining. To further assert the model's effectiveness, new optopharmacological agents were tested on the developed model, followed by visual testing. Results: Both doses of the degenerative agent induced a gradual reduction of the visual capacities of the animals. The different components of the ERG waves showed a marked decrease in their amplitude throughout the 28 days of the experiment, with the 60 mg/kg dose provoking a more pronounced functional loss. Similar results were observed in the behavioural tests, in which the animals' visual sensitivity, visual acuity, photomotor capacity were highly decreased. Same tests were performed under the effect of new optopharmacological therapies. Our results demonstrate not only the model's effectiveness, but also the usefulness of the new therapy for vision recover. Conclusions: NaIO3 induced murine model of retinal degeneration seems to be a good model for testing new pharmacological approaches to retinal diseases. Assessment of retinal function by electrophysiological tests, visual animal behaviour and retinal histology seem to be basic and reliable techniques for the evaluation of drug effect on this new animal model.