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OTX2 loss causes rod differentiation defect in CRX-associated congenital blindness

ABSTRACT: Leber congenital amaurosis (LCA) includes congenital or early-onset blinding diseases, characterized by vision loss together with nystagmus and nonrecordable electroretinogram (ERG). At least 19 genes are associated with LCA. While most LCA is recessive, mutations in the homeodomain transcription factor gene CRX lead to autosomal dominant LCA. The mechanism of CRX-LCA is not understood. Here, we report a new spontaneous mouse mutant carrying a frameshift mutation in Crx (CrxRip). We show that, unlike Crx-/- mouse retina, the dominant Crx c.763del1 mutation in CrxRip results in congenital blindness with complete loss of ERG, yet the photoreceptors do not degenerate. Dominant CRX frameshift mutations associated with LCA mimic the CrxRip phenotype that can be rescued by Crx. RNA-Seq profiling reveals progressive and complete loss of rod differentiation factor Nrl in CrxRip, while residual Nrl remains in Crx-/- retina. Moreover, Nrl partially restores the rod phenotype in CrxRip/+ mice. We show that the binding of Otx2 to Nrl promoter is obliterated in CrxRip mutant, and ectopic Otx2 can rescue the rod phenotype. Therefore, Otx2 is required to maintain Nrl expression in developing rods to consolidate rod fate. Our studies provide the mechanism of congenital blindness caused by dominant CRX mutations and should assist in therapeutic design.

ORGANISM(S): Mus musculus

PROVIDER: GSE52006 | GEO | 2014/01/13

SECONDARY ACCESSION(S): PRJNA226093

REPOSITORIES: GEO

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Project description:Rod and cone photoreceptors in mammalian retina are generated from common pool(s) of neuroepithelial progenitors. NRL, CRX and NR2E3 are key transcriptional regulators that control photoreceptor differentiation. Mutations in NR2E3, a rod-specific orphan nuclear receptor, lead to loss of rods, increased density of S-cones, and supernormal S-cone-mediated vision in humans. To better understand its in vivo function, NR2E3 was expressed ectopically in the Nrl-/- retina, where post-mitotic precursors fated to be rods develop into functional S-cones similar to the human NR2E3 disease. Expression of NR2E3 in the Nrl-/- retina completely suppressed cone differentiation and resulted in morphologically rod-like photoreceptors, which were not functional. Gene profiling of FACS-purified photoreceptors confirmed the role of NR2E3 as a strong suppressor of cone genes and an activator of a subset of rod genes (including rhodopsin) in vivo. Ectopic expression of NR2E3 in cone precursors and differentiating S-cones of wild type retina also generates rod-like cells. The dual regulatory function of NR2E3 is not dependent upon the presence of NRL and/or CRX, but on the timing and level of its expression. Our studies reveal a critical role of NR2E3 in establishing functional specificity of post-mitotic photoreceptor precursors during retinal neurogenesis. Experiment Overall Design: We mated the Crx::Nr2e3/Nrlko mice with the Nrl::GFP transgenic mice, in which the expression of GFP is driven by an Nrl promoter. Mouse retinas were dissected at 4 wk. GFP+ photoreceptors were enriched by FACS (FACSAria, BD Biosciences, Franklin Lakes, NJ). RNA was extracted from 1~5x105 flow-sorted cells using Trizol (Invitrogen). Total RNA (40-60 ng) was used for linear amplification with Ovation Biotin labeling system (Nugen), and 2.75 ug of biotin-labeled fragmented cDNA was hybridized to mouse GeneChips MOE430.2.0 (Affymetrix) having 45,101 probesets (corresponding to over 39,000 transcripts, and 34,000 annotated mouse genes). Experiment Overall Design: Four independent samples were used at 4 weeks. We normalized Experiment Overall Design: Crx::Nr2e3/Nrl-ko-Gfp data along with Nrl-ko-Gfp 4 weeks samples ( 4 replicates, refer to Series submission GSE4051). The normalized data was then subjected to two stage analysis based on False Discovery Rate Confidence Interval (FDR-CI) for screening differentially expressed genes (24, 27) with a minimum fold change of 4.

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OTX2 loss causes rod differentiation defect in CRX-associated congenital blindness

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