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Protein kinase CK2 modulates NRL-mediated gene expression in rod photoreceptors of mammalian retina

ABSTRACT: Maf-family basic motif leucine zipper protein NRL specifies rod photoreceptor cell fate during retinal development and, in concert with homeodomain protein CRX and other regulatory factors, controls the expression of most rod-expressed genes including the visual pigment gene RHO (rhodopsin). Transcriptional regulatory activity of NRL is modulated by post-translational modifications (PTMs), specially phosphorylation, and mutations in phosphosites can lead to retinal degeneration. During our studies to elucidate NRL-mediated transcriptional regulation, we identified Protein Kinase CK2 in NRL-enriched complexes bound to RHO promoter-enhancer regions and in NRL-enriched high molecular mass fractions from the bovine retina. The presence of CK2 in NRL complexes was confirmed by co-immunoprecipitation from developing and adult mouse retinal extracts. Bioinformatic and mass spectrometry analysis indicated potential phosphorylation of NRL at Ser117 residue by CK2. Co-transfection of Csnk2a1 cDNA encoding CK2 with NRL and CRX reduced the bovine Rho promoter-driven luciferase expression in HEK293 cells, and mutagenesis of NRL-Ser117 residue to Ala restored the reporter gene expression. In concordance, overexpression of CK2 in the mouse retina in vivo by electroporation resulted in reduction of Rho promoter-driven DsRed reporter gene expression. RNA-seq analysis of CK2-electroporated retina revealed altered expression of many transcriptional targets of NRL. Thus, our studies demonstrate an important role of CK2 in context-dependent fine-tuning of NRL function, consequently modulating the expression of rod photoreceptor genes.

ORGANISM(S): Mus musculus

PROVIDER: GSE171665 | GEO | 2024/04/06

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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Protein kinase CK2 modulates NRL-mediated gene expression in rod photoreceptors of mammalian retina

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