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ATAC-seq and RNA-seq of adult mouse rods and cones

ABSTRACT: 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.

ORGANISM(S): Mus musculus

PROVIDER: GSE83312 | GEO | 2017/02/09

SECONDARY ACCESSION(S): PRJNA325538

REPOSITORIES: GEO

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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.

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ATAC-seq and RNA-seq of adult mouse rods and cones

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