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: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 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: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: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. Retinal samples were harvested from WT, CrxRip/+, CrxRip/Rip, Crx-/- and Nrl-/- retina at postnatal days 2 and 21 for whole transcriptome sequencing (RNAseq). Each sample included 2 independent frozen retina and experiments were performed in duplicates. RNA-seq transcriptome libraries were constructed from 1 ?g of total RNA.
Project description:The basic motif-leucine zipper (bZIP) transcription factor NRL determines rod photoreceptor cell fate during retinal development, and its loss leads to cone-only retina in mice. NRL works synergistically with homeodomain protein Cone-Rod Homeobox and other regulatory factors to control the transcription of most genes associated with rod morphogenesis and functional maturation, which span over a period of several weeks in the mammalian retina. We predicted that NRL gradually establishes rod cell identity and function by temporal and dynamic regulation of stage-specific transcriptional targets. Therefore, we mapped the genomic occupancy of NRL at four stages of mouse photoreceptor differentiation by CUT&RUN analysis. Dynamics of NRL binding revealed concordance with the corresponding changes in transcriptome of the developing rods. Notably, we identified c-Jun proto-oncogene as one of the targets of NRL, which could bind to specific cis-elements in the c-Jun promoter and modulate its activity in HEK293 cells. Coimmunoprecipitation studies showed the association of NRL with c-Jun, also a bZIP protein, in transfected cells as well as in developing mouse retina. Additionally, shRNA-mediated knockdown of c-Jun in the mouse retina in vivo resulted in altered expression of almost 1000 genes, with reduced expression of phototransduction genes and many direct targets of NRL in rod photoreceptors. We propose that c-Jun-NRL heterodimers prime the NRL-directed transcriptional program in neonatal rod photoreceptors before high NRL expression suppresses c-Jun at later stages. Our study highlights a broader cooperation among cell-type restricted and widely expressed bZIP proteins, such as c-Jun, in specific spatiotemporal contexts during cellular differentiation.
Project description:The basic motif-leucine zipper (bZIP) transcription factor NRL determines rod photoreceptor cell fate during retinal development, and its loss leads to cone-only retina in mice. NRL works synergistically with homeodomain protein Cone-Rod Homeobox and other regulatory factors to control the transcription of most genes associated with rod morphogenesis and functional maturation, which span over a period of several weeks in the mammalian retina. We predicted that NRL gradually establishes rod cell identity and function by temporal and dynamic regulation of stage-specific transcriptional targets. Therefore, we mapped the genomic occupancy of NRL at four stages of mouse photoreceptor differentiation by CUT&RUN analysis. Dynamics of NRL binding revealed concordance with the corresponding changes in transcriptome of the developing rods. Notably, we identified c-Jun proto-oncogene as one of the targets of NRL, which could bind to specific cis-elements in the c-Jun promoter and modulate its activity in HEK293 cells. Coimmunoprecipitation studies showed the association of NRL with c-Jun, also a bZIP protein, in transfected cells as well as in developing mouse retina. Additionally, shRNA-mediated knockdown of c-Jun in the mouse retina in vivo resulted in altered expression of almost 1000 genes, with reduced expression of phototransduction genes and many direct targets of NRL in rod photoreceptors. We propose that c-Jun-NRL heterodimers prime the NRL-directed transcriptional program in neonatal rod photoreceptors before high NRL expression suppresses c-Jun at later stages. Our study highlights a broader cooperation among cell-type restricted and widely expressed bZIP proteins, such as c-Jun, in specific spatiotemporal contexts during cellular differentiation.
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).
Project description:Purpose: To investigate the gene regulatory networks during photoreceptor differentiation. Special aims: To generate gene expression profiles of purified photoreceptors at distinct developmental stages and from different genetic backgrounds. Background: Rod photoreceptor genesis spans a broad temporal window during retinal development. It starts as early as E12.5 and peaks at P0-P2. At E16.5, there are some early born rods but the peak of rod genesis does not occur. At P2, the majority of rod photoreceptors are born. At P6, rod specific structural/functional genes begin to express. At P10, Outer segments morphogenesis is taking place. At 4 weeks, retinal development is complete and retina is functional. Nrl is a rod specific transcription factor and one of the earliest markers of rod photoreceptors. Nrl promoter drives the expression of GFP exclusively to rod photoreceptors shortly after they exit cell cycle. In the Nrl-knockout background, the expression of GFP is detected in S-opsin positive cells, which suggested a cell fate transformation from rods to cones in the absence of Nrl. Design: GFP positive photoreceptors from the WT-Gfp or Nrl-knockout-Gfp retina were enriched (purified) by FACS at five distinct developmental stages (E16, P2, P6, P10, and 4 weeks). Total RNA was extracted by Trizol reagent. Around 50 ng of total RNA was used for linear amplification and biotin labeling followed Nugen kit protocol. Fragmented cDNA was hybridized on Affymetrix mouse genomic expression array 430 2.0 and then scanned with the standard protocol. Four replicates were performed for each time point. Conclusion: By comparing the gene expression profiles from different developmental stages, we can obtain novel insights into molecular events underlying photoreceptor differentiation. Keywords: Transcription factor, development, photoreceptor, retina, neuron, differentiation, gene regulation, microarray, gene profiling, cell type comparison