RNA-mediated symmetry breaking enables singular olfactory receptor choice

AD Pourmorady and EV Bashkirova and AM Chiariello and H Belagzhal and A Kodra and R DuffiƩ and J Kahiapo and K Monahan and J Pulupa and I Schieren and A Osterhoudt and J Dekker and M Nicodemi and S Lomvardas, NATURE (2023).

DOI: 10.1038/s41586-023-06845-4

Olfactory receptor (OR) choice provides an extreme example of allelic competition for transcriptional dominance, where every olfactory neuron stably transcribes one of approximately 2,000 or more OR alleles1,2. OR gene choice is mediated by a multichromosomal enhancer hub that activates transcription at a single OR3,4, followed by OR-translation- dependent feedback that stabilizes this choice5,6. Here, using single- cell genomics, we show formation of many competing hubs with variable enhancer composition, only one of which retains euchromatic features and transcriptional competence. Furthermore, we provide evidence that OR transcription recruits enhancers and reinforces enhancer hub activity locally, whereas OR RNA inhibits transcription of competing ORs over distance, promoting transition to transcriptional singularity. Whereas OR transcription is sufficient to break the symmetry between equipotent enhancer hubs, OR translation stabilizes transcription at the prevailing hub, indicating that there may be sequential non-coding and coding mechanisms that are implemented by OR alleles for transcriptional prevalence. We propose that coding OR mRNAs possess non-coding functions that influence nuclear architecture, enhance their own transcription and inhibit transcription from their competitors, with generalizable implications for probabilistic cell fate decisions. Messenger RNAs transcribed from olfactory-receptor genes may have non-coding functions that include recruitment of transcriptional enhancers and inhibition of potentially thousands of competing alleles to ensure stable transcription of a single allele.

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