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Olfactory receptor mRNAs act as selfish non-coding RNAs that enforce transcriptional singularity (OR Switching Experiment)

ABSTRACT: To investigate roles for olfactory receptor coding sequence mRNA in trans olfactory receptor gene silencing, and OR-gene enhancer recruitment. Olfactory receptor (OR) choice provides an extreme example of allelic competition for transcriptional dominance, as every olfactory neuron stably transcribes one out of more than ~2,000 OR alleles1,2. OR gene choice is mediated by a multi-chromosomal enhancer hub that activates transcription at a single OR3,4, followed by ORtranslation dependent feedback that stabilizes this choice5,6. However, with more than one OR enhancer hub in each nucleus7, the mechanism by which only one OR allele is chosen for transcription remains enigmatic. Here, using single cell genomics, we show that only one of the OR enhancer hubs formed in each neuron retains euchromatic features and sustains transcriptional competence. Further, we provide evidence that OR transcription recruits enhancers and reinforces enhancer hub activity locally, while OR RNA inhibits transcription in competing hubs over distance, promoting OR protein-independent transition to singularity. While OR RNA synthesis is sufficient to break the symmetry between equipotent enhancer hubs, OR translation stabilizes transcription at the prevailing hub, revealing dual non-coding and coding mechanisms implemented by OR RNAs for transcriptional prevalence. We propose that coding mRNAs can function as “selfish” non-coding RNAs that influence nuclear architecture, enhance their own transcription, and inhibit their competitors, with generalizable implications in probabilistic cell fate decisions.

ORGANISM(S): Mus musculus

PROVIDER: GSE240023 | GEO | 2023/09/28

REPOSITORIES: GEO

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Project description:Distant enhancer elements are a major source of specificity in mammalian gene expression. Although enhancers that regulate broad developmental decisions and inducible gene expression have been studied extensively, little is known about regulatory elements that govern monogenic and monoallelic expression. Here, using high throughput epigenetic and genetic techniques we identified a plethora of distant enhancers that regulate monoallelic olfactory receptor (OR) gene expression. Potential OR enhancers have unique, cell type specific epigenetic marks that distinguish them from other neuronal enhancers and correlate with enhancer activity in vivo. Using sequence capture to enrich for these sequences we identified Dnase-protected footprints that reveal novel regulatory sequences and transcription factors required for OR gene activation. Our experiments provide insight to the regulation of OR expression, and describe novel principles and methodologies towards the understanding of transcriptional mechanisms that generate cellular diversity. In vivo examination of H3K79me3 enrichment and DNAse protected footprints on olfactory receptor enhancer sequences. We performed ChIP-seq on native chromatin isolated from the mouse olfactory epithelium using antibodies against H3K79me3. To sequence accessible regions of the genome we treated nuclei with limiting amounts of DNAse I to digest accessible chromatin and perform Dnase Hypersensitivity (DHS)-seq. In the olfactory epithelium, the H enhancer – the first described enhancer for olfactory receptors has a well-defined DNAse I hypersensitivity peak and is flanked by high levels of H3K79me3. We find other intergenic sequences nearby olfactory receptor genes that share the same chromatin signature, and test their function in vivo. TO uncover transcription factor footprints on olfactory receptor enhancers we performed sequence capture of the DHS-seq library to enrich for these sequences. We find multiple DNAse-protected sequences and perform motif analysis on transcription factor footprints to reveal factors involved in olfactory receptor gene regulation.

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Olfactory receptor mRNAs act as selfish non-coding RNAs that enforce transcriptional singularity (OR Switching Experiment)

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