Project description:Both rod and cone photoreceptors are critical for mammalian vision yet they have important functional differences. In this study, we investigate patterns of DNA methylation and chromatin accessibility in mouse rods and cones. Unexpectedly, we find that a substantial fraction of hypo-methylated regions in the rod methylome are in inaccessible chromatin. These regions show marks of active regulatory regions earlier in neuronal development and could remain undermethylated in adult rods due to their highly compact chromatin. We further identify rod- and cone-enriched regions of accessible chromatin that correspond with cell type-specificity of nearby photoreceptor gene expression. We predict novel DNA signatures of rod and cone specificity and show that NR2E3 function is necessary for rods to gain their complete ensemble of epigenomic features. Taken together, our data capture the epigenomic landscapes of retinal rods and cones, including differences relevant to chromatin structure and photoreceptor biology.
Project description:The macula of the retina has a high ratio of cones to rods and is critical for central vision and visual acuity. Macula degenerations affect vision the most and are incurable. Here we report the generation, transcriptome profiling, and functional validation of cone-enriched human retinal organoids differentiated from hESCs. Transcriptome profiling using bulk RNA-seq demonstrated that retinal differentiation in vitro recapitulated retinogenesis in vivo in the temporal expression of cell differentiation markers and retinal disease genes, as well as in mRNA alternative splicing. Single-cell RNA-seq of 8-month retinal organoids identified clusters of cone and rod photoreceptors and confirmed the cone enrichment initially revealed by immunostaining. Notably, comparisons of single-cell transcriptomes demonstrated the similarity between retinal organoids and human macula in cones and rods. Cones in retinal organoids exhibited electrophysiological functions. Collectively, we have established cone-enriched retinal organoids and a reference of transcriptomes that are rich resources for retinal studies.
Project description:Rod photoreceptors are specialized neurons that mediate vision in dim light and are the predominant photoreceptor type in nocturnal mammals. The rods of nocturnal mammals are unique among vertebrate cell types in having an 'inverted' nuclear architecture, with a single dense mass of heterochromatin in the center of the nucleus rather than dispersed clumps at the nuclear periphery. We hypothesized that this unique chromatin organization would correlate with a unique epigenomic landscape as defined by chromatin accessibility. To test this idea, we performed open chromatin profiling (ATAC-seq) on purified mouse rods and their most closely related cell type, cone photoreceptors, which revealed that thousands of loci are selectively closed in rods. Comparison with open-chromatin maps from >60 additional cell types and tissues demonstrated that rods have by far the most closed chromatin architecture. To explore how the unique epigenomic landscape of rods is controlled, we profiled photoreceptors purified from mice lacking the rod master regulator Nrl. We find that the open-chromatin profile of Nrl-/- photoreceptors is nearly indistinguishable from that of native cones, indicating that Nrl is necessary to achieve selective chromatin closure in rods. Finally, we identified distinct enrichments of transcription factor binding sites in rods and cones, suggesting specific mechanisms by which rods and cones encode cell type-specific information in regulatory DNA. Taken together, these data provide new insight into the development and maintenance of photoreceptor identity, and highlight rods as an attractive system for studying the relationship between nuclear organization and local changes in chromatin accessibility.
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:Cone photoreceptor cell death in inherited retinal diseases, such as Retinitis Pigmentosa (RP), leads to the loss of accurate and color vision and ultimately blindness. In RP, a vast number of mutations are affecting the structure and function of rod photoreceptors while cones remain mutation-free. Once majority of rods have degenerated cones are dying secondarily due to the increased oxidative stress, inflammation and loss of structural and nutritional support normally provided by rods. Here we demonstrated that secondary cone cell death in animal models for RP is governed by an increased activity of histone deacetylates (HDACs). A single intravitreal injection of an HDAC inhibitor at a late stage of the disease, when majority of rods have already degenerated, is sufficient to delay cone death and support long-term cone survival. Surviving cones are retaining functionality and are mediating light-driven ganglion cell responses. RNA-seq analysis of surviving cones demonstrated that HDAC inhibition affords multi-level protection trough regulation of different prosurvival pathways including MAPK, PI3K-AKT and autophagy. These study suggest a unique possibility for targeted pharmacological protection of both primary degenerating rods and mutation-free secondary dying cones and creates hope to maintain vision in RP patients independent of the disease stage.
Project description:Vertebrate ancestors had only cone-like photoreceptors. The duplex retina evolved in jawless vertebrates with the advent of highly photosensitive rod-like photoreceptors. Despite cones being the arbiters of high-resolution color vision, rods emerged as the dominant photoreceptor in mammals during a nocturnal phase early in their evolution. We investigated the evolutionary and developmental origins of rods in two divergent vertebrate retinae. In mice, we discovered genetic and epigenetic vestiges of short wavelength cones in developing rods and cell lineage tracing validated the genesis of rods from S-cones. Curiously, rods did not derive from S-cones in zebrafish. Our study illuminates several questions regarding the evolution of duplex retina and supports the hypothesis that, in mammals, the S-cone lineage was recruited via the Maf-family transcription factor NRL to augment rod photoreceptors. We propose that this developmental mechanism allowed the adaptive exploitation of scotopic niches during the nocturnal bottleneck early in mammalian evolution.
Project description:The macula of the retina has a high ratio of cones to rods and is critical for central vision and visual acuity. Here we report the generation, transcriptome profiling, and functional validation of single cells from cone-enriched human retinal organoids differentiated from hESCs. Single-cell RNA-seq of 8-month retinal organoids identified clusters of cone and rod photoreceptors and confirmed the cone enrichment initially revealed by immunostaining. Collectively, we have established cone-enriched retinal organoids and a reference of transcriptomes that are rich resources for retinal studies.
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).