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Targeting of GFP to new-born rods by Nrl promoter and temporal expression profiling of flow-sorted photoreceptors

ABSTRACT: 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

ORGANISM(S): Mus musculus

PROVIDER: GSE4051 | GEO | 2006/02/28

SECONDARY ACCESSION(S): PRJNA95193

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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Targeting of GFP to new-born rods by Nrl promoter and temporal expression profiling of flow-sorted photoreceptors

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