Project description:Nrl acts as a molecular toggle switch during retinal development: if a photoreceptor precursor turns on Nrl, it differentiates as a rod, otherwise it differentiates as a cone. In contrast, acute Nrl knockout transforms mature rods into cells with features intermediate between those of normal rods and cones (‘cods’). We used microarray to comprehensively evaluate the transcriptomic changes that occur upon acute knockout of Nrl in mouse retina.
Project description:The initial aim of this work was to understand the pathophysiology of Enhanced S-cone Syndrome (ESCS) that leads to retinal degeneration. Although ESCS was identified in humans decades ago and since then the causative genes have been elucidated, our understanding of the accompanying retinal degeneration is still poorly understood. Knockout of the Nrl transcription factor in mice produces a retina overpopulated with S-cone like photoreceptors along with absence of rod photoreceptors and recapitulates many of the phenotypic features seen in human ESCS patients. We wanted to study this murine model through a combinatorial genetic and structural approach to improve understanding of the disease process that leads to photoreceptor degeneration and blindness, potentially guiding future therapies. By using RNA-Sequencing (RNA-Seq) to examine mature wild type and Nrl-/- ocular tissues, we were able to determine global changes in their transcriptomes. The massively parallel RNA-sequencing experiment revealed new insight into the transcriptional mis-regulation in the ESCS murine model and revealed a change in gene expression in putative proteins involved in photoreceptor phagocytosis. Key photoreceptor ligands necessary for phagocyotsis, Tub and Tulp1, were down-regulated in the Nrl-/- retina. Down regulation of key retinoid metabolic genes, coupled with down-regulation of Tub and Tulp1, suggested a potential mechanism involving defective phagocytosis underlies the photoreceptor degeneration seen in ESCS. We report RNA-Seq experiments of whole eye and retinal tissues from wild type and Nrl transcription factor knockout mice on the C57BL/6 background. Examine two different ocular tissues in two mouse models of varying photoreceptor populations
Project description:The rod photoreceptor-specific neural retina leucine zipper protein Nrl is essential for rod differentiation and plays a critical role in regulating gene expression. In the mouse retina, rods account for 97% of the photoreceptors; however, in the absence of Nrl (Nrl-/-), no rods are present and a concomitant increase in cones is observed. Using mouse GeneChips (Affymetrix), we have generated expression profiles of the wild-type and Nrl-/- retina at three time-points representing distinct stages of photoreceptor differentiation. Experiment Overall Design: Both the Nrl-/- mice and wild type controls were of a matched mixed genetic background (R1 and C57BL/6 strains).
Project description:The rod photoreceptor-specific neural retina leucine zipper protein Nrl is essential for rod differentiation and plays a critical role in regulating gene expression. In the mouse retina, rods account for 97% of the photoreceptors; however, in the absence of Nrl (Nrl-/-), no rods are present and a concomitant increase in cones is observed. Using mouse GeneChips (Affymetrix), we have generated expression profiles of the wild-type and Nrl-/- retina at three time-points representing distinct stages of photoreceptor differentiation. Keywords: time course
Project description:We performed mRNA transcriptional profiling of mouse retina in the wild-type and Nrl-null context to determine Nrl-dependent gene expression We sequenced cDNA libraries made from polyA+ selected RNA from retinas of litter-matched WT and Nrl-/- adult mice at postnatal day 21 (P21) (WT vs Nrl-/-, n=5 and n= 6 resp.)
Project description:The initial aim of this work was to understand the pathophysiology of Enhanced S-cone Syndrome (ESCS) that leads to retinal degeneration. Although ESCS was identified in humans decades ago and since then the causative genes have been elucidated, our understanding of the accompanying retinal degeneration is still poorly understood. Knockout of the Nrl transcription factor in mice produces a retina overpopulated with S-cone like photoreceptors along with absence of rod photoreceptors and recapitulates many of the phenotypic features seen in human ESCS patients. We wanted to study this murine model through a combinatorial genetic and structural approach to improve understanding of the disease process that leads to photoreceptor degeneration and blindness, potentially guiding future therapies. By using RNA-Sequencing (RNA-Seq) to examine mature wild type and Nrl-/- ocular tissues, we were able to determine global changes in their transcriptomes. The massively parallel RNA-sequencing experiment revealed new insight into the transcriptional mis-regulation in the ESCS murine model and revealed a change in gene expression in putative proteins involved in photoreceptor phagocytosis. Key photoreceptor ligands necessary for phagocyotsis, Tub and Tulp1, were down-regulated in the Nrl-/- retina. Down regulation of key retinoid metabolic genes, coupled with down-regulation of Tub and Tulp1, suggested a potential mechanism involving defective phagocytosis underlies the photoreceptor degeneration seen in ESCS.
Project description:NRL (Neural retina leucine zipper) is a key regulator of the fate determination and gene expression of rod photoreceptors in the retina of many vertebrates. In this study, we observed a unique retinal phenotype in the nrl knockout zebrafish model characterized by reduced rods with shortened outer segments and gradually increased green-cones in adulthood. By tracing and comparing the developmental processes of WT and nrl knockout rods, we found there might be two waves of rod genesis distinguished as nrl-dependent and independent with different starting times. To reveal the underlying cellular and molecular mechanisms, bulk and single-cell RNA-seq were performed. The changes in gene expression and cell proportion of rods and cones agreed well with our histological and immunofluorescence studies. Interestingly, we found that rods exhibited noticeable heterogeneities in the gene expression patterns, and a part of rods in nrl knockout zebrafish misexpressed the green-cone genes, reflecting a hybrid status of rod and green-cone. Furthermore, we identified mafba as a novel regulator of rod genesis, which was responsible for the development of rods in nrl knockout zebrafish. Our study will largely improve the current understanding of the developmental processes and regulatory mechanisms of rods in zebrafish and probably other species, and may facilitate future studies in the fields of retinal development and retinal degeneration.
Project description:NRL (Neural retina leucine zipper) is a key regulator of the fate determination and gene expression of rod photoreceptors in the retina of many vertebrates. In this study, we observed a unique retinal phenotype in the nrl knockout zebrafish model characterized by reduced rods with shortened outer segments and gradually increased green-cones in adulthood. By tracing and comparing the developmental processes of WT and nrl knockout rods, we found there might be two waves of rod genesis distinguished as nrl-dependent and independent with different starting times. To reveal the underlying cellular and molecular mechanisms, bulk and single-cell RNA-seq were performed. The changes in gene expression and cell proportion of rods and cones agreed well with our histological and immunofluorescence studies. Interestingly, we found that rods exhibited noticeable heterogeneities in the gene expression patterns, and a part of rods in nrl knockout zebrafish misexpressed the green-cone genes, reflecting a hybrid status of rod and green-cone. Furthermore, we identified mafba as a novel regulator of rod genesis, which was responsible for the development of rods in nrl knockout zebrafish. Our study will largely improve the current understanding of the developmental processes and regulatory mechanisms of rods in zebrafish and probably other species, and may facilitate future studies in the fields of retinal development and retinal degeneration.
Project description: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.
Project description:Cone photoreceptors are the primary initiator of visual transduction in the human retina. Dysfunction or death of rod photoreceptors precedes cone loss in many retinal and macular degenerative diseases, suggesting a rod-dependent trophic support for cone survival. Rod differentiation and homeostasis are dependent on the basic motif leucine zipper transcription factor NRL. The loss of Nrl in mice (Nrl-/-) results in a retina with predominantly S-opsin containing cones that exhibit molecular and functional characteristics of WT cones. Here we report that Nrl-/- retina undergoes a rapid but transient period of degeneration in early adulthood, with cone apoptosis, retinal detachment, alterations in retinal vessel structure, and activation and translocation of retinal microglia. However, cone degeneration stabilizes by four months of age, resulting in a thinned but intact outer nuclear layer with residual cones expressing S- and M-opsins and a preserved photopic ERG. At this stage, microglia translocate back to the inner retina and reacquire a quiescent morphology. Gene profiling analysis during the period of transient degeneration reveals misregulation of stress response and inflammation genes, implying their involvement in cone death. The Nrl-/- retina illustrates the long-term viability of cones in the absence of rods and may serve as a model for elucidating mechanisms of cone homeostasis and degeneration that would be relevant to understanding diseases of the cone-dominant human macula. Targets were generated from a pair of retinas (one Nrl-/- mouse) per biological replicate. Four biological replicates were generated for each of the five aging timepoints (1, 2, 4, 6, and 10 months post natal).