Olfactory receptor (OR) choice, the transcriptional activation of one out of thousands of available mammalian OR alleles, is a poorly understood process. We previously demonstrated that the nuclear intra- and inter- chromosomal aggregation of OR genes in a few, OR-specific, heterochromatic foci contributes to the efficient OR silencing, preserving the monogenic and monoallelic nature of OR expression. Here, we examine the hypothesis that complex interchromosomal associations are responsible also for the transcriptional activation of a single OR allele. Using high throughput epigenetic and genetic approaches we identified a set of novel OR enhancers that support reporter expression in significant fractions of olfactory sensory neurons in zebrafish and mice. Our preliminary data suggest that these enhancers might work in concert for the activation of OR expression, creating a structural and functional singularity in the nuclei of olfactory sensory neurons. We propose a series of experiments that will map and quantify the interchromosomal associations of the newly identified enhancers using imaging and Hi-C approaches. Moreover, we propose genetic loss-, and gain-of- function experiments that will test whether OR enhancers act synergistically towards the activation of a single OR allele. Finally, we seek to investigate the contribution of the unusual epigenetic signature of OR enhancers in their function and nuclear organization. Our experiments will provide novel insight into the role of nuclear architecture in gene expression and will uncover molecular mechanisms involved in the generation of cellular diversity in vivo.
The recent realization that nuclear architecture might influence gene expression promises to solve long lasting regulatory problems of mammalian differentiation and development in health and disease. Using the genetically and biochemically tractable mouse olfactory system to reveal principles of nuclear organization and how this regulates transcription, will advance our understanding of this paradigm-shifting regulatory process and will provide insight to the long lasting mystery of olfactory receptor choice.
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