Olfactory Sensory Neuron Diversity Beyond OR Genes in mice [scRNAseq]
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ABSTRACT: How functional cellular heterogeneities are regulated is fundamental for understanding the molecular basis of complex organs. Olfactory sensory neurons (OSNs) are an ideal model to investigate the regulation of cellular heterogeneity. The “one-neuron-one-receptor” organization and topographical mapping ensure the detection and precise translation of odor signals to the central neural system. Besides the diversity of OR genes and other molecular guiding axon sorting processes, single-cell transcriptome analysis revealed an OSN subpopulation, defined by Cd36, a lipid receptor gene. The function study exhibited lipid odor identification was impaired in Cd36-deficient mice. In this study, we systematically depicted the transcriptome diversity, spatial distribution, and specific functions of Cd36+ OSNs in the mouse olfactory epithelium. The specific molecular features of Cd36+ OSN we revealed implemented the programmed cellular diversity may be driven by their olfaction function. Furthermore, with the integrative analysis of single-cell transcriptome and epigenome profiles, we revealed the cis and trans regulatory signatures in Cd36+ OSN and identified Tshz1 and Mef2 as the key regulators that may directly regulate and promote the expression of Cd36 and drive the cellular diversity of OSNs. Especially, we demonstrated that Tshz1 is expressed coordinately with the choices of ORs, earlier than the expression of Cd36, which indicates it may act as a pioneer factor that instructs the lineage-specific expression of Cd36 and other genes, eventually leading to the cellular diversity of Cd36+ OSN. Our results provide novel knowledge on the regulation mechanism of cellular diversity of complex organs.
Project description:How functional cellular heterogeneities are regulated is fundamental for understanding the molecular basis of complex organs. Olfactory sensory neurons (OSNs) are an ideal model to investigate the regulation of cellular heterogeneity. The “one-neuron-one-receptor” organization and topographical mapping ensure the detection and precise translation of odor signals to the central neural system. Besides the diversity of OR genes and other molecular guiding axon sorting processes, single-cell transcriptome analysis revealed an OSN subpopulation, defined by Cd36, a lipid receptor gene. The function study exhibited lipid odor identification was impaired in Cd36-deficient mice. In this study, we systematically depicted the transcriptome diversity, spatial distribution, and specific functions of Cd36+ OSNs in the mouse olfactory epithelium. The specific molecular features of Cd36+ OSN we revealed implemented the programmed cellular diversity may be driven by their olfaction function. Furthermore, with the integrative analysis of single-cell transcriptome and epigenome profiles, we revealed the cis and trans regulatory signatures in Cd36+ OSN and identified Tshz1 and Mef2 as the key regulators that may directly regulate and promote the expression of Cd36 and drive the cellular diversity of OSNs. Especially, we demonstrated that Tshz1 is expressed coordinately with the choices of ORs, earlier than the expression of Cd36, which indicates it may act as a pioneer factor that instructs the lineage-specific expression of Cd36 and other genes, eventually leading to the cellular diversity of Cd36+ OSN. Our results provide novel knowledge on the regulation mechanism of cellular diversity of complex organs.
Project description:Odor discrimination behavior displays circadian fluctuations in mice indicating that mammalian olfactory function is under control of the circadian system. This is further supported by the facts that odor discrimination rhythms depend on the presence of clock genes and that olfactory tissues contain autonomous circadian clocks. However, the molecular link between circadian function and olfactory processing is still unknown. In order to elucidate the molecular mechanisms underlying this link, we focused on the olfactory epithelium (OE), the primary target of odors and the site of the initial events in olfactory processing. We asked whether olfactory sensory neurons (OSNs) within the OE possess an autonomous circadian clock and whether olfactory pathways are under circadian control. Employing clock gene-driven bioluminescence reporter assays, immunohistochemistry and a time-dependent microarray-based transcriptome analysis on OE samples, we found robust circadian rhythms of core clock genes and their proteins in OSNs, suggesting that the OE indeed contains an autonomous circadian clock. Furthermore, we identified several OSN-specific components of the olfactory pathway that are under circadian control, including several candidates with putative roles in circadian olfactory processing, such as KIRREL2 -- an established factor involved in short-term OSN activation. The spatiotemporal expression patterns of our candidate proteins suggest that they are involved in short-term anabolic processes to rhythmically prepare the cell for peak performances and to promote circadian function of OSNs. We performed a genome-wide expression study with RNA from OE tissue extracted at 4-h intervals in constant darkness from previously entrained mice. Total RNA of four mice per sampling time was pooled in equal amounts.
Project description:Odor discrimination behavior displays circadian fluctuations in mice indicating that mammalian olfactory function is under control of the circadian system. This is further supported by the facts that odor discrimination rhythms depend on the presence of clock genes and that olfactory tissues contain autonomous circadian clocks. However, the molecular link between circadian function and olfactory processing is still unknown. In order to elucidate the molecular mechanisms underlying this link, we focused on the olfactory epithelium (OE), the primary target of odors and the site of the initial events in olfactory processing. We asked whether olfactory sensory neurons (OSNs) within the OE possess an autonomous circadian clock and whether olfactory pathways are under circadian control. Employing clock gene-driven bioluminescence reporter assays, immunohistochemistry and a time-dependent microarray-based transcriptome analysis on OE samples, we found robust circadian rhythms of core clock genes and their proteins in OSNs, suggesting that the OE indeed contains an autonomous circadian clock. Furthermore, we identified several OSN-specific components of the olfactory pathway that are under circadian control, including several candidates with putative roles in circadian olfactory processing, such as KIRREL2 -- an established factor involved in short-term OSN activation. The spatiotemporal expression patterns of our candidate proteins suggest that they are involved in short-term anabolic processes to rhythmically prepare the cell for peak performances and to promote circadian function of OSNs.
Project description:The cell surface metalloprotease ADAM17 and its binding partners iRhom2 and iRhom1 modulate cell-cell interactions by mediating the release of membrane proteins such as TNFa and EGFR-ligands from the cell surface. Most cell types express both iRhoms, though myeloid cells exclusively express iRhom2, and iRhom1 is the main iRhom in the mouse brain. Here we report that iRhom2 is uniquely expressed in olfactory sensory neurons (OSNs), highly specialized cells expressing one olfactory receptor (OR) from a repertoire of over a thousand OR genes in mice. iRhom2-/- mice had no evident morphological defects in the olfactory epithelium (OE), yet RNAseq analysis revealed differential expression of a small subset of ORs. Notably, while the majority of ORs remain unaffected in iRhom2-/- OE, OSNs expressing ORs that are enriched in iRhom2-/- OE showed fewer gene expression changes upon odor environmental changes than the majority of OSNs. Moreover, we discovered an inverse correlation between the expression of iRhom2 compared to OSN activity genes and that odor exposure negatively regulates iRhom2 expression. Given that ORs are specialized G-protein coupled receptors (GPCRs) and many GPCRs activate iRhom2/ADAM17, we investigated if ORs could activate iRhom2/ADAM17. Activation of OR2AT4 by its agonist sandalore in keratinocytes, where this receptor is ectopically expressed, leads to ERK1/2 phosphorylation, likely via an iRhom2/ADAM17-dependent pathway. Taken together, these findings point to a mechanism by which odor stimulation of OSNs activates iRhom2/ADAM17 catalytic activity, resulting in downstream transcriptional changes to the OR repertoire and activity genes, and driving a negative feedback loop to downregulate iRhom2 expression.
Project description:The goal of this study was to identify those odorant receptors conferring a response to indole or related odorants (2-methylindole, 3-methylindole, 6-methylindole, 2-methoxynaphthalene, and Lilyflore®) in olfactory sensory neurons (OSNs). Odorants were sequentially delivered to dissociated OSNs, and six OSNs with three different response profiles were isolated for transcriptome analysis. OSN1 and OSN2 responded to indole, 2-methylindole, 3-methylindole, and 6-methylindole; OSN3 and OSN4 responded to Indole and 2-methoxynaphthalene; OSN5 and OSN6 responded to indole, 3-methylindole, 6-methylindole, and 2-methoxynaphthalene. RNA transcripts encoding Olfr740 (OSN1, OSN2), Olfr741 (OSN3, OSN4), and Olfr743 (OSN5, OSN6) were retrieved, with high level expression of a single OR transcript in each OSN. The expression of mature OSN markers OMP, Golf, Adcy3, Cnga2 and Rtp1 was also confirmed.
Project description:Olfactory sensory neurons (OSNs) express a single abundant olfactory receptor (OR). To assess the differences in gene expression between different OSN sub-types we collected three pools of neurons that express one OR and compared them to three pools of neurons that express another. After extracting RNA from these pools, the samples were multiplexed and sequenced using the Illumina Hiseq2500 platform.This data is part of a pre-publication release. For information on the proper use of pre-publication data shared by the Wellcome Trust Sanger Institute (including details of any publication moratoria), please see http://www.sanger.ac.uk/datasharing/
Project description:Olfactory sensory neurons (OSNs) are functionally defined by their expression of a unique odorant receptor (OR). Mechanisms underlying singular OR expression are well studied, and involve a massive cross-chromosomal enhancer interaction network. Trace amine-associated receptors (TAARs) form a distinct family of olfactory receptors, and here we find that mechanisms regulating Taar gene choice display many unique features. The epigenetic signature of Taar genes in TAAR OSNs is different from that in OR OSNs. We further identify that two TAAR enhancers conserved across placental mammals are absolutely required for expression of the entire Taar gene repertoire. Deletion of either enhancer dramatically decreases the expression probabilities of different Taar genes, while deletion of both enhancers completely eliminates the TAAR OSN populations. In addition, both of the enhancers are sufficient to drive transgene expression in the partially overlapped TAAR OSNs. We also show that the TAAR enhancers operate in cis to regulate Taar gene expression. Our findings reveal a coordinated control of Taar gene choice in OSNs by two remote enhancers, and provide an excellent model to study molecular mechanisms underlying formation of an olfactory subsystem.
Project description:Olfactory sensory neurons (OSNs) are functionally defined by their expression of a unique odorant receptor (OR). Mechanisms underlying singular OR expression are well studied, and involve a massive cross-chromosomal enhancer interaction network. Trace amine-associated receptors (TAARs) form a distinct family of olfactory receptors, and here we find that mechanisms regulating Taar gene choice display many unique features. The epigenetic signature of Taar genes in TAAR OSNs is different from that in OR OSNs. We further identify that two TAAR enhancers conserved across placental mammals are absolutely required for expression of the entire Taar gene repertoire. Deletion of either enhancer dramatically decreases the expression probabilities of different Taar genes, while deletion of both enhancers completely eliminates the TAAR OSN populations. In addition, both of the enhancers are sufficient to drive transgene expression in the partially overlapped TAAR OSNs. We also show that the TAAR enhancers operate in cis to regulate Taar gene expression. Our findings reveal a coordinated control of Taar gene choice in OSNs by two remote enhancers, and provide an excellent model to study molecular mechanisms underlying formation of an olfactory subsystem.
Project description:Olfactory sensory neurons (OSNs) are functionally defined by their expression of a unique odorant receptor (OR). Mechanisms underlying singular OR expression are well studied, and involve a massive cross-chromosomal enhancer interaction network. Trace amine-associated receptors (TAARs) form a distinct family of olfactory receptors, and here we find that mechanisms regulating Taar gene choice display many unique features. The epigenetic signature of Taar genes in TAAR OSNs is different from that in OR OSNs. We further identify that two TAAR enhancers conserved across placental mammals are absolutely required for expression of the entire Taar gene repertoire. Deletion of either enhancer dramatically decreases the expression probabilities of different Taar genes, while deletion of both enhancers completely eliminates the TAAR OSN populations. In addition, both of the enhancers are sufficient to drive transgene expression in the partially overlapped TAAR OSNs. We also show that the TAAR enhancers operate in cis to regulate Taar gene expression. Our findings reveal a coordinated control of Taar gene choice in OSNs by two remote enhancers, and provide an excellent model to study molecular mechanisms underlying formation of an olfactory subsystem.
Project description:Olfactory sensory neurons (OSNs) are functionally defined by their expression of a unique odorant receptor (OR). Mechanisms underlying singular OR expression are well studied, and involve a massive cross-chromosomal enhancer interaction network. Trace amine-associated receptors (TAARs) form a distinct family of olfactory receptors, and here we find that mechanisms regulating Taar gene choice display many unique features. The epigenetic signature of Taar genes in TAAR OSNs is different from that in OR OSNs. We further identify that two TAAR enhancers conserved across placental mammals are absolutely required for expression of the entire Taar gene repertoire. Deletion of either enhancer dramatically decreases the expression probabilities of different Taar genes, while deletion of both enhancers completely eliminates the TAAR OSN populations. In addition, both of the enhancers are sufficient to drive transgene expression in the partially overlapped TAAR OSNs. We also show that the TAAR enhancers operate in cis to regulate Taar gene expression. Our findings reveal a coordinated control of Taar gene choice in OSNs by two remote enhancers, and provide an excellent model to study molecular mechanisms underlying formation of an olfactory subsystem.