Interrogating genome folding trajectories in health and disease

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Project Summary Detection and identification of the astronomical number of volatile chemicals that we perceive as odors depends upon the monogenic and monoallelic expression of olfactory receptor (OR) genes in olfactory sensory neurons (OSNs). An intricate network of OSN-specific interchromosomal interactions coordinates the transcriptional activation of only 1 OR allele out of >2000 OR alleles distributed across 18 different chromosomes. Genomic interactions between silent OR genes assemble heterochromatic multi-chromosomal compartments that keep OR genes transcriptionally inactive, whereas genomic interactions between intergenic OR enhancers result in a multi-chromosomal enhancer hub that activates singular OR transcription. Here, we propose to combine Dip-C, a variation of single cell HiC, with viral-based cell tagging technologies, towards the identification of genome folding intermediates across OSN differentiation lineages. This “cradle to crate” genomic analysis will follow individual OSN progenitors and their barcoded progeny, allowing a complete cartography of genomic interactions made by every OR allele en route to transcriptional activation. Single molecule DNA FISH experiments will complement the proposed genomic studies, providing high resolution insight to the genomic choreography that orchestrates singular OR gene choice during development. Finally, we seek to explore how the trajectories of OSN genomic folding become altered and eventually disrupted in a humanized model for Alzheimer’s disease (AD). Olfactory dysfunction, hyposmia, and anosmia constitute well- established prodromal symptoms of AD, but the molecular etiology of this intriguing connection is not known. Using a humanized model for AD we discovered that interchromosomal OR compartments dissipate prior to the onset of neurodegeneration, resulting in strong downregulation of OR transcription. Thus, we propose to apply our single cell interrogation of genome folding transition in the context of AD and to establish the baseline of nuclear architecture in human OSNs. Deciphering how OR compartments assemble in health, and how they become disrupted in disease, may provide the basis for novel prognostic and diagnostic tools for AD, and molecular assays for in vivo screening of AD therapeutics.