Project description:The laminated structure of the retina is fundamental for the organization of the synaptic circuitry that translates light input into patterns of action potentials. However, the molecular mechanisms underlying cell migration and layering of the retina are poorly understood. Here, we show that RBX2, a core component of the E3 ubiquitin ligase CRL5, is essential for retinal layering and function. RBX2 regulates the final cell position of rod bipolar cells, cone photoreceptors and Muller glia. Our data indicate that sustained RELN/DAB1 signaling, triggered by depletion of RBX2 or SOCS7 - a CRL5 substrate adaptor known to recruit DAB1 - causes rod bipolar cell misposition. Moreover, whereas SOCS7 also controls Muller glia cell lamination, it is not responsible for cone photoreceptor positioning, suggesting that RBX2, most likely through CRL5 activity, controls other signaling pathways required for proper cone localization. Furthermore, RBX2 depletion reduces the number of ribbon synapses and disrupts cone photoreceptor function. Together, these results uncover RBX2 as a crucial molecular regulator of retina morphogenesis and cone photoreceptor function.
Project description:Primary and secondary cone photoreceptor cell death in retinal degenerative diseases, including age-related macular degeneration and retinitis pigmentosa, leads to severe vision impairment and blindness. Regardless of the fact that protection of cone photoreceptor cells under stress conditions, such as retinal degenerative diseases, is crucial for maintaining vision, the underlying molecular mechanisms are unclear. Here, we investigated the function of the deubiquitinase Otud7b/Cezanne in the retina. We identified that Otud7b is predominantly expressed in photoreceptor cells in the mouse retina. While the ablation of Otud7b did not cause a significant defect in development and maturation of the mouse retina, Otud7b‒/‒ mice subjected to light-induced damage, which is one of the dry age-related macular degeneration models, exhibited increased cone photoreceptor degeneration. In addition, Otud7b deficiency in Mak‒/‒ mice, a retinitis pigmentosa mouse model, resulted in further cone photoreceptor degeneration. Moreover, neuronal cells deficient in Otud7b were susceptible to serum starvation, resulting in cell death. We found that NF-κB activity is increased in the Otud7b‒/‒ retinas exposed to light by RNA-sequencing analysis. Luciferase reporter assay also demonstrated increased NF-κB activation in Otud7b-deficient neuronal cells under stress. The neuronal cell death resulting from Otud7b deficiency was suppressed through the inhibition of NF-κB. Furthermore, we observed that inhibition of NF-κB attenuated cone photoreceptor degeneration in the light-exposed Otud7b‒/‒ retina. Together, the current study suggests that Otud7b deubiquitinase protects cone photoreceptor cells under stress conditions by modulating the NF-κB activity.
Project description:The human retina has unique features that are not all fully replicated in animal models. Several human-specific features center on cone photoreceptors such as a cone-rich fovea, three cone types, and the cone precursor’s proliferative response to RB1 loss. Prior droplet-based single cell RNA-sequencing (scRNA-seq) datasets have not clearly defined cone precursor developmental states or gene expression patterns. To further elucidate photoreceptor developmental trajectories, we FACS-enriched cone and rod precursors and retinal progenitor cells from eighteen Fetal Week 13-19 retina and performed deep, full-length scRNA-seq. These data were used to evaluate post-mitotic photoreceptor precursor trajectories, accompanying gene expression changes, and cone-specific features that drive the cone precursor proliferative response.
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. Keywords: genetic modification
Project description:The differentiation of cone photoreceptors, which mediate daylight vision and color vision, depends critically upon thyroid hormone.However, the route of access of blood-borne thyroid hormone to cones is undefined because cones reside behind the blood-retina barrier. This study uses genetic manipulation of a membrane transporter for thyroid hormone (Mct8) in mouse models to show a role for the retinal pigment epithelium (RPE), which forms the outer blood-retina barrier, in the control of cone differentiation.The results suggest a paracrine-like mechanism promotes thyroid hormone-mediated cone differentiation. The findings suggest that in addition to the transport of essential solutes and support of photoreceptor homeostasis, the RPE controls hormonal signaling required for cone differentiation.
Project description:Photoreceptor loss is a leading cause of blindness, but mechanisms underlying photoreceptor degeneration are not well understood. Treatment strategies would benefit from an improved understanding of gene-expression patterns directing photoreceptor development, as many genes are implicated in both development and degeneration. Neural retina leucine zipper (NRL) is critical for rod photoreceptor genesis and degeneration, with NRL mutations known to cause enhanced S-cone syndrome and retinitis pigmentosa. While murine Nrl loss has been characterized, studies of human NRL can identify important insights for human retinal disease. Here we utilized human organoid models of retinal development to molecularly define developmental alterations in a human model of NRL loss. Consistent with the function of NRL in rod fate specification, human retinal organoids lacking NRL develop S-opsin dominant photoreceptor populations. We report generation of two distinct S-opsin expressing populations in NRL null retinal organoids and identify MEF2C as a candidate regulator of cone development.
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:Death of photoreceptors and/or Retinal Pigment Epithelium (RPE) cells is a common cause of age related and inherited retinal dystrophies, thus their replenishment from renewable stem cell sources is a well sought therapeutic goal. Human pluripotent stem cells provide a useful cell source in view of their limitless self-renewal capacity and potential to differentiate into all key retinal cell types either in isolation or as part of three dimensional retinal organoids. Photoreceptor precursors have been isolated from differentiating human pluripotent stem cells either through application of cell surface markers or fluorescent reporter approaches and shown to share a transcriptional profile akin to foetal photoreceptors. In this study we investigated the transcriptional profile of CRX+ photoreceptor precursors derived from human embryonic stem cells (hESC) using single cell RNA sequencing and their engraftment capacity in an animal model of retinitis pigmentosa (C3H/rd1). Single cell RNA seq analysis revealed the presence of dominant cell cluster which displayed the hallmarks of early cone photoreceptor expression. When transplanted subretinally into the C3H/rd1 mice, the Crx positive cells settled next to the inner nuclear layer of host retina, matured into cone photoreceptors and made connections with the inner neurones of the host retina. Cellular transfer between the host retina and donor photoreceptors was investigated and shown to be minimal. Together our data provide valuable molecular insights into the transcriptional profile of human pluripotent stem cells derived CRX+ photoreceptor precursors and indicate their usefulness as a source of transplantable cone photoreceptors.
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.