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Differentiation of developing olfactory neurons analysed in terms of coupled epigenetic landscapes.

ABSTRACT: The olfactory system integrates signals from receptors expressed in olfactory sensory neurons. Each sensory neuron expresses only one of many similar olfactory receptors (ORs). The choice of receptor is made stochastically early in the differentiation process and is maintained throughout the life of the neuron. The underlying mechanism of this stochastic commitment to one of multiple similar OR genes remains elusive. We present a theoretical analysis of a mechanism that invokes important epigenetic properties of the system. The proposed model combines nucleosomes and associated read-write enzymes as mediators of a cis-acting positive feedback with a trans-acting negative feedback, thereby coupling the local epigenetic landscape of the individual OR genes in a way that allow one and only one gene to be active at any time. The model pinpoint that singular gene selection does not require transient mechanisms, enhancer elements or transcription factors to separate choice from maintenance. In addition, our hypothesis allow us to combine all reported characteristics of singular OR gene selection, in particular that OR genes are silenced from OR transgenes. Intriguingly, it predicts that OR transgenes placed in close proximity should always be expressed simultaneously, though rarely.

SUBMITTER: Alsing AK

PROVIDER: S-EPMC3643594 | biostudies-literature | 2013 May

REPOSITORIES: biostudies-literature

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Differentiation of developing olfactory neurons analysed in terms of coupled epigenetic landscapes.

Alsing Anne Katrine AK Sneppen Kim K

Nucleic acids research 20130321 9

The olfactory system integrates signals from receptors expressed in olfactory sensory neurons. Each sensory neuron expresses only one of many similar olfactory receptors (ORs). The choice of receptor is made stochastically early in the differentiation process and is maintained throughout the life of the neuron. The underlying mechanism of this stochastic commitment to one of multiple similar OR genes remains elusive. We present a theoretical analysis of a mechanism that invokes important epigene ...[more]

PMID: 23519617

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Project description:During differentiation, neurons experience a reorganization of DNA modification patterns within their genomes. However, the mechanisms underlying this developmental patterning and its role in defining the neuronaÂÂl state are currently unclear. Here, we find that the dÂÂe novo DNA methyltransferase Dnmt3a is necessary for elevated levels of 5-hydroxymethylcytosine (5hmC), a derivative of 5-methylcytosine (5mC), in olfactory sensory neurons (OSNs). Through an analysis of genome-wide 5mC and 5hmC distributions in isolated OSNs, we find that Dnmt3a-dependent 5mC and 5hmC occurs within regions of high accessibility, neural enhancers, and the transcription start sites of transcribed genes. Its loss results in the global disruption of gene expression patterns, including the upregulation of silent genes, the downregulation of mOSN-expressed genes, and the alteration of odorant-induced transcriptional responses of immediate early genes. Together, these results demonstrate that Dnmt3a is necessary to define the neuronal transcriptional state and may be broadly involved in refining expression profiles within differentiated cells. To determine the contributions of Dnmt3a to the DNA modification and transcriptional landscapes of a post-mitotic neuronal population, we performed DNA immunoprecipitation (DIP-seq) using antibodies specific for 5mC and 5hmC and rRNA-depleted transcriptional profiling (RNA-seq) coupled to high-throughput sequencing using genomic DNA or RNA from FACS-isolated mature olfactory sensory neurons (mOSNs) from main olfactory epithelium (MOE) of Dnmt3a wildtype (WT), heterozygous-null (Het), or homozygous-null (KO) 3-week old mice. Similarly, to compare this information with other epigenetic features of the MOE, we performed H3K4me1 (WT), H3K27ac (WT), and H3K27me3 (WT and KO) chromatin immunoprecipitation (ChIP)-seq and DNase I hypersensitivity assays (DNase-seq) using MOE nuclei from 3-week old mice. In addition, we assayed the influence of Dnmt3a-deficiency on the induction of odorant-responsive genes by exposing 3-week old Dnmt3a WT, Het, and KO mice to either water or a 1:1:1 mixture of amyl acetate:acetophenone:octanal for 1 hour and performed rRNA-depleted RNA-seq using RNA isolated from their MOEs.

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Differentiation of developing olfactory neurons analysed in terms of coupled epigenetic landscapes.

Publications

Differentiation of developing olfactory neurons analysed in terms of coupled epigenetic landscapes.

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