Decoding the olfactory map: targeted transcriptomics link olfactory receptors to glomeruli

Sensory processing in vertebrate olfactory systems is organized across olfactory bulb glomeruli, wherein axons of peripheral sensory neurons expressing the same olfactory receptor co-terminate to transmit receptor-specific activity to central neurons. Understanding how receptors map to glomeruli is therefore critical to understanding olfaction. High-throughput spatial transcriptomics is a rapidly advancing field, but low-abundance olfactory receptor expression within glomeruli has previously precluded high-throughput mapping of receptors to glomeruli. Here we combined spatial sectioning along the anteroposterior, dorsoventral, and mediolateral axes with target capture enrichment sequencing to overcome low-abundance target expression. This strategy allowed us to spatially map 86% of olfactory receptors across the olfactory bulb and uncover a relationship between OR sequence and glomerular position.

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Organization and distribution of glomeruli in the bowhead whale olfactory bulb

10.7287/peerj.preprints.740 ◽

2014 ◽

Author(s):

Takushi Kishida ◽

J. G. M. Thewissen ◽

Sharon Usip ◽

John C George ◽

Robert S Suydam

Keyword(s):

Olfactory Bulb ◽

Olfactory Receptor ◽

Olfactory Receptors ◽

Molecular Data ◽

Dorsal Side ◽

Bowhead Whale ◽

Model Organisms ◽

Marker Genes ◽

Baleen Whales ◽

Olfactory Receptor Genes

Although modern baleen whales still possess a functional olfactory systems that includes olfactory bulbs, cranial nerve I and olfactory receptor genes, their olfactory capabilities have been reduced profoundly. This is probably in response to their fully aquatic lifestyle. The glomeruli that occur in the olfactory bulb can be divided into two non-overlapping domains, a dorsal domain and a ventral domain. Recent molecular studies revealed that all modern whales have lost olfactory receptor genes and marker genes that are specific to the dorsal domain, and that a modern baleen whale possess only 60 olfactory receptor genes. Here we show that olfactory bulb of bowhead whales (Balaena mysticetus, Mysticeti) lacks glomeruli on the dorsal side, consistent with the molecular data. In addition, we estimate that there are more than 4,000 glomeruli in the bowhead whale olfactory bulb. Olfactory sensory neurons that express the same olfactory receptor in mice generally project to two specific glomeruli in an olfactory bulb, meaning that ratio of the number of olfactory receptors : the number of glomeruli is approximately 1:2. However, we show here that this ratio is not applicable to whales, indicating the limitation of mice as model organisms for understanding the initial coding of odor information among mammals.

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Coordinating Receptor Expression and Wiring Specificity in Olfactory Receptor Neurons

10.1101/594895 ◽

2019 ◽

Cited By ~ 4

Author(s):

Hongjie Li ◽

Tongchao Li ◽

Felix Horns ◽

Jiefu Li ◽

Qijing Xie ◽

...

Keyword(s):

Olfactory Receptor ◽

Olfactory Receptors ◽

Receptor Expression ◽

Olfactory Receptor Neurons ◽

Unique Combination ◽

Axon Targeting ◽

Transcriptional Regulatory ◽

Receptor Neurons ◽

Transcriptional Regulatory Mechanisms ◽

The Brain

The ultimate function of a neuron is determined by both its physiology and connectivity, but the transcriptional regulatory mechanisms that coordinate these two features are not well understood1–4. The Drosophila Olfactory receptor neurons (ORNs) provide an excellent system to investigate this question. As in mammals5, each Drosophila ORN class is defined by the expression of a single olfactory receptor or a unique combination thereof, which determines their odor responses, and by the single glomerulus to which their axons target, which determines how sensory signals are represented in the brain6–10. In mammals, the coordination of olfactory receptor expression and wiring specificity is accomplished in part by olfactory receptors themselves regulating ORN wiring specificity11–13. However, Drosophila olfactory receptors do not instruct axon targeting6, 14, raising the question as to how receptor expression and wiring specificity are coordinated. Using single-cell RNA-sequencing and genetic analysis, we identified 33 transcriptomic clusters for fly ORNs. We unambiguously mapped 17 to glomerular classes, demonstrating that transcriptomic clusters correspond well with anatomically and physiologically defined ORN classes. We found that each ORN expresses ~150 transcription factors (TFs), and identified a master TF that regulates both olfactory receptor expression and wiring specificity. A second TF plays distinct roles, regulating only receptor expression in one class and only wiring in another. Thus, fly ORNs utilize diverse transcriptional strategies to coordinate physiology and connectivity.

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Ectopic olfactory receptors in the respiratory system

Russian Pulmonology ◽

10.18093/0869-0189-2019-29-6-734-738 ◽

2020 ◽

Vol 29 (6) ◽

pp. 734-738

Author(s):

V. N. Mineev

Keyword(s):

Smooth Muscle ◽

Olfactory Receptor ◽

Olfactory Receptors ◽

Receptor Activation ◽

Neuroendocrine Cells ◽

Receptor Expression ◽

Special Role ◽

Concentration Data ◽

Cell Functions

New findings and concepts on a role of so-called “ectopic” chemosensory receptors arise recently. The ectopic receptors are expressed outside their classical localization (nasal cavity) and referred to as extra-nasal olfactory receptors. Functional investigations of the ectopic olfactory receptors in the lungs are also ongoing. To date, it is well-known that molecules of odorous substances (odorants) bind to the G-protein-associated olfactory receptor (Gαolf) that can activate type III adenylate cyclase and increase concentration of a secondary messenger, cyclic adenosine monophosphate (cAMP). In turn, this induces the opening of cAMP-dependent cationic channels including calcium channels. Olfactory receptor activation in neuroendocrine cells of the lungs affected serotonin release which decreased after the stimulation of those cells by an odorant. Amyl butyrate and burgenal, agonists of OR2AG1 and OR1D2 olfactory receptors, respectively, affect smooth muscle contractibility in human bronchi. Amyl butyrate inhibits histamine-induces muscle contractibility, whereas burgenal increases the smooth muscle contractibility. Both the processes are mediated by cAMP-dependent increase in the intracellular calcium concentration. Data have been published about the receptor expression on immune cells such as monocytes, natural killers, T- and B-lymphocites, and polymorphonuclears. Ectopic olfactory receptors are thought to participate in modulation (controlling) of intrinsic cell functions which provide a special role of inflammatory cells in asthma. In future, the olfactory receptor modulation could be probably used as a novel therapeutic approach in asthma and other chronic inflammatory lung diseases.

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The structural basis of odorant recognition in insect olfactory receptors

Nature ◽

10.1038/s41586-021-03794-8 ◽

2021 ◽

Author(s):

Josefina del Mármol ◽

Mackenzie A. Yedlin ◽

Vanessa Ruta

Keyword(s):

Olfactory Receptor ◽

Hydrophobic Interactions ◽

Olfactory Receptors ◽

Binding Pocket ◽

Structural Basis ◽

Structural Determinants ◽

Cryo Electron Microscopy ◽

Common Strategy ◽

Olfactory Systems ◽

Discriminatory Capacity

AbstractOlfactory systems must detect and discriminate amongst an enormous variety of odorants1. To contend with this challenge, diverse species have converged on a common strategy in which odorant identity is encoded through the combinatorial activation of large families of olfactory receptors1–3, thus allowing a finite number of receptors to detect a vast chemical world. Here we offer structural and mechanistic insight into how an individual olfactory receptor can flexibly recognize diverse odorants. We show that the olfactory receptor MhOR5 from the jumping bristletail4Machilis hrabei assembles as a homotetrameric odorant-gated ion channel with broad chemical tuning. Using cryo-electron microscopy, we elucidated the structure of MhOR5 in multiple gating states, alone and in complex with two of its agonists—the odorant eugenol and the insect repellent DEET. Both ligands are recognized through distributed hydrophobic interactions within the same geometrically simple binding pocket located in the transmembrane region of each subunit, suggesting a structural logic for the promiscuous chemical sensitivity of this receptor. Mutation of individual residues lining the binding pocket predictably altered the sensitivity of MhOR5 to eugenol and DEET and broadly reconfigured the receptor’s tuning. Together, our data support a model in which diverse odorants share the same structural determinants for binding, shedding light on the molecular recognition mechanisms that ultimately endow the olfactory system with its immense discriminatory capacity.

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Organization and distribution of glomeruli in the bowhead whale olfactory bulb

10.7287/peerj.preprints.740v1 ◽

2014 ◽

Author(s):

Takushi Kishida ◽

J. G. M. Thewissen ◽

Sharon Usip ◽

John C George ◽

Robert S Suydam

Keyword(s):

Olfactory Bulb ◽

Olfactory Receptor ◽

Olfactory Receptors ◽

Molecular Data ◽

Dorsal Side ◽

Bowhead Whale ◽

Model Organisms ◽

Marker Genes ◽

Baleen Whales ◽

Olfactory Receptor Genes

Although modern baleen whales still possess a functional olfactory systems that includes olfactory bulbs, cranial nerve I and olfactory receptor genes, their olfactory capabilities have been reduced profoundly. This is probably in response to their fully aquatic lifestyle. The glomeruli that occur in the olfactory bulb can be divided into two non-overlapping domains, a dorsal domain and a ventral domain. Recent molecular studies revealed that all modern whales have lost olfactory receptor genes and marker genes that are specific to the dorsal domain, and that a modern baleen whale possess only 60 olfactory receptor genes. Here we show that olfactory bulb of bowhead whales (Balaena mysticetus, Mysticeti) lacks glomeruli on the dorsal side, consistent with the molecular data. In addition, we estimate that there are more than 4,000 glomeruli in the bowhead whale olfactory bulb. Olfactory sensory neurons that express the same olfactory receptor in mice generally project to two specific glomeruli in an olfactory bulb, meaning that ratio of the number of olfactory receptors : the number of glomeruli is approximately 1:2. However, we show here that this ratio is not applicable to whales, indicating the limitation of mice as model organisms for understanding the initial coding of odor information among mammals.

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Olfactory Receptor Gene Regulation in Insects: Multiple Mechanisms for Singular Expression

Frontiers in Neuroscience ◽

10.3389/fnins.2021.738088 ◽

2021 ◽

Vol 15 ◽

Author(s):

Kaan Mika ◽

Richard Benton

Keyword(s):

Olfactory Receptor ◽

Internal State ◽

Receptor Gene ◽

Expression Patterns ◽

Olfactory Receptors ◽

Regulatory Elements ◽

Receptor Expression ◽

Outstanding Question ◽

The Brain ◽

Large Repertoire

The singular expression of insect olfactory receptors in specific populations of olfactory sensory neurons is fundamental to the encoding of odors in patterns of neuronal activity in the brain. How a receptor gene is selected, from among a large repertoire in the genome, to be expressed in a particular neuron is an outstanding question. Focusing on Drosophila melanogaster, where most investigations have been performed, but incorporating recent insights from other insect species, we review the multilevel regulatory mechanisms of olfactory receptor expression. We discuss how cis-regulatory elements, trans-acting factors, chromatin modifications, and feedback pathways collaborate to activate and maintain expression of the chosen receptor (and to suppress others), highlighting similarities and differences with the mechanisms underlying singular receptor expression in mammals. We also consider the plasticity of receptor regulation in response to environmental cues and internal state during the lifetime of an individual, as well as the evolution of novel expression patterns over longer timescales. Finally, we describe the mechanisms and potential significance of examples of receptor co-expression.

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Olfactory receptor–dependent receptor repression in Drosophila

Science Advances ◽

10.1126/sciadv.abe3745 ◽

2021 ◽

Vol 7 (32) ◽

pp. eabe3745

Author(s):

Kaan Mika ◽

Steeve Cruchet ◽

Phing Chian Chai ◽

Lucia L. Prieto-Godino ◽

Thomas O. Auer ◽

...

Keyword(s):

Olfactory Receptor ◽

Regulatory Networks ◽

Receptor Gene ◽

Gene Array ◽

Receptor Expression ◽

Specific Gene ◽

Coding Region ◽

Ionotropic Receptor ◽

Olfactory Systems ◽

In Cis

In olfactory systems across phyla, most sensory neurons express a single olfactory receptor gene selected from a large genomic repertoire. We describe previously unknown receptor gene–dependent mechanisms that ensure singular expression of receptors encoded by a tandem gene array [Ionotropic receptor 75c (Ir75c), Ir75b, and Ir75a, organized 5′ to 3′] in Drosophila melanogaster. Transcription from upstream genes in the cluster runs through the coding region of downstream loci and inhibits their expression in cis, most likely via transcriptional interference. Moreover, Ir75c blocks accumulation of other receptor proteins in trans through a protein-dependent, posttranscriptional mechanism. These repression mechanisms operate in endogenous neurons, in conjunction with cell type–specific gene regulatory networks, to ensure unique receptor expression. Our data provide evidence for inter-olfactory receptor regulation in invertebrates and highlight unprecedented, but potentially widespread, mechanisms for ensuring exclusive expression of chemosensory receptors, and other protein families, encoded by tandemly arranged genes.

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Investigating Molecular Mechanisms of Immunotoxicity and the Utility of ToxCast for Immunotoxicity Screening of Chemicals Added to Food

International Journal of Environmental Research and Public Health ◽

10.3390/ijerph18073332 ◽

2021 ◽

Vol 18 (7) ◽

pp. 3332

Author(s):

Olga V. Naidenko ◽

David Q. Andrews ◽

Alexis M. Temkin ◽

Tasha Stoiber ◽

Uloma Igara Uche ◽

...

Keyword(s):

Immune System ◽

High Throughput ◽

Environmental Protection Agency ◽

High Throughput Screening ◽

Molecular Mechanisms ◽

Specific Activity ◽

Laboratory Animals ◽

In Vitro Assays ◽

Toxicological Studies

The development of high-throughput screening methodologies may decrease the need for laboratory animals for toxicity testing. Here, we investigate the potential of assessing immunotoxicity with high-throughput screening data from the U.S. Environmental Protection Agency ToxCast program. As case studies, we analyzed the most common chemicals added to food as well as per- and polyfluoroalkyl substances (PFAS) shown to migrate to food from packaging materials or processing equipment. The antioxidant preservative tert-butylhydroquinone (TBHQ) showed activity both in ToxCast assays and in classical immunological assays, suggesting that it may affect the immune response in people. From the PFAS group, we identified eight substances that can migrate from food contact materials and have ToxCast data. In epidemiological and toxicological studies, PFAS suppress the immune system and decrease the response to vaccination. However, most PFAS show weak or no activity in immune-related ToxCast assays. This lack of concordance between toxicological and high-throughput data for common PFAS indicates the current limitations of in vitro screening for analyzing immunotoxicity. High-throughput in vitro assays show promise for providing mechanistic data relevant for immune risk assessment. In contrast, the lack of immune-specific activity in the existing high-throughput assays cannot validate the safety of a chemical for the immune system.

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Molecular Modelling of Oligomeric States of DmOR83b, an Olfactory Receptor in D. Melanogaster

Bioinformatics and Biology Insights ◽

10.4137/bbi.s8990 ◽

2012 ◽

Vol 6 ◽

pp. BBI.S8990 ◽

Cited By ~ 6

Author(s):

K. Harini ◽

R. Sowdhamini

Keyword(s):

Olfactory Receptor ◽

Olfactory Receptors ◽

Insect Species ◽

Agricultural Pests ◽

Negative Effects ◽

C Terminus ◽

Receptor Neurons ◽

Medical Importance ◽

G Protein Coupled ◽

Made In

After the discovery of the complete repertoire of D. melanogaster Olfactory Receptors (ORs), candidate ORs have been identified from at least 12 insect species from four orders (Coleoptera, Lepidoptera, Diptera, and Hymenoptera), including species of economic or medical importance. Although all ORs share the same G-protein coupled receptor structure with seven transmembrane domains, they share poor sequence identity within and between species, and have been identified mainly through genomic data analyses. To date, D. melanogaster remains the only insect species where ORs have been extensively studied, from expression pattern establishment to functional investigations. These studies have confirmed several observations made in vertebrates: one OR type is selectively expressed in a subtype of olfactory receptor neurons, and one olfactory neuron expresses only one type of OR. The olfactory mechanism, further, appears to be conserved between insects and vertebrates. Understanding the function of insect ORs will greatly contribute to the understanding of insect chemical communication mechanisms, particularly with agricultural pests and disease vectors, and could result in future strategies to reduce their negative effects. In this study, we propose molecular models for insect olfactory receptor co-receptor OR83b and its possible functional oligomeric states. The functional similarity of OR83b to GPCRs and ion channels has been exploited for understanding the structure of OR83b. We could observe that C-terminal region (TM4-7) of OR83b is involved in homodimer amd heterodimer formation (with OR22a) which suggests why C-terminus of insect ORs are highly conserved across different species. We also propose two possible ion channel pathways in OR83b: one formed by TM4-5 region with intracellular pore-forming domain and the other formed by TM5-6 with extracellular pore forming domain using analysis of the electrostatics distribution of the pore forming domain.

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