Project description:The photoreceptor outer segment is the canonical example of a modified and highly specialised cilium, with an expanded membrane surface area in the form of discs or lamellae for efficient light detection. Many ciliary proteins are essential for normal photoreceptor function and cilium dysfunction often results in retinal degeneration leading to impaired vision. Herein, we investigate the function and localisation of the ciliary G-protein RAB28 in zebrafish cone photoreceptors. CRISPR-Cas9 generated rab28 mutant zebrafish display a reduction in shed outer segment material in the RPE at 1 month post fertilisation (mpf), but otherwise normal retinal structure and visual function up to 12 mpf. Cone photoreceptorspecific transgenic reporter lines show Rab28 localises almost exclusively to outer segments, independently of nucleotide binding. Co-immunoprecipitation analysis demonstrates tagged Rab28 interacts with components of the phototransduction cascade, including opsins, Phosphodiesterase 6C and Guanylate Cyclase 2D. Our data shed light on RAB28 function in cones and provide a model for RAB28-associated cone-rod dystrophy
Project description:To investigate pathogenic mechanisms in such instances, we have characterized rod photoreceptor and retinal gene expression changes in response to a defined insult to photoreceptor structure, using the retinal degeneration slow (rds) mouse model. Global gene expression profiling was performed on flow-sorted rds and wild-type rod photoreceptors immediately prior and subsequent to times at which OSs are normally elaborated. Dysregulated genes were identified via microarray hybridization, and selected candidates were validated using quantitative PCR analyses. We identified a single key gene, Egr1, that was dysregulated in a sustained fashion in rds rod photoreceptors and in the retina. Egr1 upregulation was associated with microglial activation and migration, into the outer retina at times subsequent to the major peak of photoreceptor cell death. Interestingly, this response was accompanied by neurotrophic factor upregulation. We hypothesize that activation of Egr1 and neurotrophic factors represents a protective immune mechanism, contributing to the characteristically slow retinal degeneration of the rds mouse model. We had two conditions WT and Rds-KO at 4 different time points: postnatal (P) 6, P9, P14 and P21.
Project description:Results: Our histologic studies indicated that human retinal organoids (HROs) at day 200 of differentiation in this system are postmitotic and thus completed retinogenesis. Further, HRO contain all major retinal cell types in a laminated structure. Notably, HROs are cone photoreceptor-rich, show a 1:1:1 ratio of Müller glia, rod and cone photoreceptor. Immunostaining and ultrastructural studies showed that photoreceptors neurons mature, including photoreceptor inner and nascent outer segment formation. Our transcriptome analysis at the single cell level supports these findings. Further, comparison with published datasets (Voigt et al. 2019 [PMID: 31075224]) indicate that the genotype of cone photoreceptors in this HRO system correlates more strongly with the foveal cones of the human primary retina than peripheral cones. Müller glia show a trend towards human fovea whereas rod photoreceptors were found to be nearly similar. Conclusions: Single cell transcriptome analysis of HROs support and extend our findings at the histological level, indicating that HROs are cone photoreceptor-rich, and provide some characteristics of the human macula.
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
Project description:Complexin (Cplx)3 and Cplx4, SNARE-complex-regulators of the Cplx family, have been proposed to be involved in the light adaptation of ribbon synapses by limiting synaptic vesicle (SV) recruitment and fusion, but how this Cplx effect is exerted is unknown. Focusing on light adaptation of rod photoreceptor ribbon synapses, we first applied gel-based proteomics to FACS-sorted cone and rod photoreceptor cells to show that Cplx4 is the predominant Cplx in mouse rod photoreceptors, a finding that was confirmed by immunocytochemistry and RT-qPCR analyses. To uncover the functional network linking Cplx4 to light adaptation, we developed a quantitative proteomic screen to identify proteins that specifically interact with the Cplx4-SNARE complex at rod photoreceptor ribbon synapses. For affinity purification, detergent-extracted mouse retina lysates were incubated with Cplx peptide-coupled beads. Eluted proteins were subjected to in-solution digestion and analyzed by label-free quantification. We identified the G protein Transducin, a key molecule of the phototransduction cascade and known to translocate from the photoreceptor outer segment to the presynaptic terminal in light, as a component of the Cplx4-SNARE complex.
Project description:To investigate pathogenic mechanisms in such instances, we have characterized rod photoreceptor and retinal gene expression changes in response to a defined insult to photoreceptor structure, using the retinal degeneration slow (rds) mouse model. Global gene expression profiling was performed on flow-sorted rds and wild-type rod photoreceptors immediately prior and subsequent to times at which OSs are normally elaborated. Dysregulated genes were identified via microarray hybridization, and selected candidates were validated using quantitative PCR analyses. We identified a single key gene, Egr1, that was dysregulated in a sustained fashion in rds rod photoreceptors and in the retina. Egr1 upregulation was associated with microglial activation and migration, into the outer retina at times subsequent to the major peak of photoreceptor cell death. Interestingly, this response was accompanied by neurotrophic factor upregulation. We hypothesize that activation of Egr1 and neurotrophic factors represents a protective immune mechanism, contributing to the characteristically slow retinal degeneration of the rds mouse model.
Project description:The rd1 mouse retina is a well-studied model of retinal degeneration where rod photoreceptors undergo cell death beginning at postnatal day P10 until P21. This period coincides with photoreceptor terminal differentiation in a normal retina. We have used the rd1 retina as a model to investigate early molecular defects in developing rod photoreceptors prior to the onset of degeneration. Using a microarray approach, we performed gene profiling comparing rd1 and wild type retinas at four time points starting at P2, prior to any obvious biochemical or morphological differences, and concluding at P8, prior to the initiation of cell death. We have identified genes that are differentially regulated in the rd1 retina at early time points, which may give insights into developmental defects that precede photoreceptor cell death. This is the first report of PRA1 expression in the retina. Our data support the hypothesis that PRA1 plays an important role in vesicular trafficking between the Golgi and cilia in differentiating and mature rod photoreceptors. Retinal samples were harvested from both rd1/le and wt animals at postnatal days 2, 4, 6, and 8 for microarray. Each sample included 8-14 retinas and experiments were performed in quadruplicate. Ten micrograms of total RNA was used for cDNA systhesis in target molecule production.
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.
Project description:The outer segments of cones serve as light detectors for daylight color vision, and their dysfunction leads to human blindness conditions. We show that the cone-specific disruption of DiGeorge Syndrome Critical Region Gene 8 (DGCR8) in adult mice led to the loss of miRNAs and the loss of outer segments, resulting in photoreceptors with significantly reduced light responses. Using next-generation sequencing of RNA from isolated wild type P60 cones, we determine the most highly expressed miRNAs as candidates for controlling outer segment maintenance. The expression pattern of miRNAs was highly uneven, with a single miRNA, miR-182, representing 64% of all miRNA expressed in cones. Re-expression of miR-182 and miR-183 (third most abundant miRNA) prevented outer segment loss. These miRNAs were also necessary and sufficient for the formation of inner segments, connecting cilia and short outer segments, as well as light responses in stem-cell-derived retinal cultures. Our results show that miR-182- and miR-183-regulated pathways are necessary for cone outer segment maintenance in vivo and functional outer segment formation in vitro. microRNA profile in cone photoreceptors from P60 D4-cre/Ai9 tdTomato mice representing wild type control.