Olfactory Receptor Family Research Articles

Ectopically Expressed Human Olfactory Receptor OR51E1: a Search for Novel Molecular Probes

Olfactory receptors comprise the largest family of G protein‐couples receptors (GPCRs) ‐ ~1400 functional genes in the mouse (Olfrs) and ~400 in the human (ORs). Most genes were assigned to it based solely on the sequence similarity. Recent studies demonstrated that many Olfrs are expressed outside of the nasal cavity and possibly involved in physiological processes such as muscle regeneration and controlling blood pressure. These ectopically expressed olfactory receptors might recognize cues other than odorants and be involved in processes independent of the sense of smell. Ligands were identified for fewer than 100 of ORs and Olfrs.Using transcriptomics analysis followed by RT‐PCR and in situ RNA hybridization we previously showed expression of several Olfrs and other olfactory signaling genes expressed in the mouse ocular tissues. We focused our attention on Olfr558 and demonstrated its expression in blood vessels of the eye. The human ortholog of Olfr558 (OR51E1 or PSGR2) was shown to be expressed in the prostate and dramatically up‐regulated in prostate cancer and is an established biomarker of malignancy. The human and mouse genes encoding this receptor are almost identical (94%), which is unique for GPCRs in general, and particularly for sensory chemoreceptors. This unusual evolutionary conservation points to the importance of its physiological function. While the function of this receptor or its native ligand is unknown, in vitro it responds to some short‐ and medium‐chain fatty acids (e.g., butyrate and valerate) by activating adenylyl cyclase. We found that growth of human prostate cancer cells that express OR51E1 is inhibited by valerate. The knockdown of OR51E1 gene with shRNA eliminated this effect of valerate.While butyrate and valerate can be used in such experiments, their low affinity and selectivity complicates interpretation of the data. Additionally, they are quickly metabolized in the body. Thus, there is a clear need for novel probes that can be used to dissect OR51E1 function. To address this need, we established a stable cell line overexpressing OR51E1 and demonstrated that in response to known OR51E1 agonists this cell line increases intracellular cAMP level. We then used this cell line for screening of a diverse chemical library of 9600 compounds, showing its suitability for high throughput screening. To demonstrate that our expression system can be used for expression of other ORs, we generated stable cell lines overexpressing two other receptors – OR51E2 and OR2AT4. We showed that both receptors are expressed as proteins of the expected molecular weight and localize on the cell surface. Since these ORs represents a large class of previously unexplored yet druggable targets, this project facilitates investigation of the entire family of ectopic olfactory receptors.

<p>LncRNA OR3A4 Regulated the Growth of Osteosarcoma Cells by Modulating the miR-1207-5p/G6PD Signaling</p>

BackgroundIncreasing evidence has demonstrated the importance of non-coding RNAs including long non-coding RNA (lncRNA) and microRNAs (miRNAs) in the tumorigenesis of osteosarcoma (OS). Abnormal expression of lncRNA olfactory receptor family 3 subfamily A member 4 (OR3A4) was found in multiple human cancers; however, the function of OR3A4 in OS remains largely unknown.Materials and MethodsThe expression level of OR3A4 in OS tissues and cell lines was detected by RT-qPCR. Cell counting kit-8 assay, colony formation and flow cytometry analysis were performed to determine the growth of OS cells. The targets of OR3A4 were predicted using the miRDB database. The binding between OR3A4 and miRNAs was confirmed by dual-luciferase reporter assay.ResultsOR3A4 was overexpressed in OS tissues and correlated with the advanced progression of OS patients. Down-regulation of OR3A4 significantly inhibited the proliferation and colony formation of OS cells. Mechanistically, OR3A4 acted as a sponge of miR-1207-5p. Glucose-6-phosphate dehydrogenase (G6PD) was identified as a target of miR-1207-5p. Knockdown of OR3A4 increased the expression of miR-1207-5p and consequently, suppressed the level of G6PD in OS cells. Due to the essential role of G6PD in the pentose phosphate pathway (PPP), depletion of OR3A4 inhibited NADPH production, glucose consumption and lactate generation. Decreased level of NADPH by depletion of OR3A4 up-regulated the redox state (ROS) content and resulted in endoplasmic reticulum (ER) stress in OS cells. Restoration of G6PD significantly attenuated the cell growth inhibition induced by OR3A4 knockdown.ConclusionOur finding suggested the critical role of OR3A4 in the proliferation of OS cells via targeting the miR-1207-5p/G6PD axis.

A Group of Olfactory Receptor Alleles that Encode Full Length Proteins are Down-Regulated as Olfactory Sensory Neurons Mature

The family of olfactory receptors (ORs) subserves the sense of smell and includes both functional alleles and pseudogenes, the latter identified by mutations resulting in frame shift or premature truncation. During neuronal differentiation, nonfunctional ORs are expressed initially but then are switched out, and/or the olfactory sensory neurons (OSNs) expressing them die. We carried out a transcriptomic analysis of FACS-isolated cells from ΔSox2-eGFP, Neurog1-eGFP BAC and ΔOMP-eGFP strains of uninjured and olfactory bulbectomized transgenic mice that correspond to distinct stages in the progression from globose basal cell stem cells to fully mature OSNs. We analyzed the expression pattern of 1094 unique receptors across this progression and found that the vast majority were characterized by a typical and expected pattern of expression; i.e., levels of OR mRNA peaking in mature OSNs. However, 43 ORs, including several known pseudogenes, were different, such that mRNA expression declined in the mature OSNs relative to earlier stages. Protein and promoter sequence analysis of the atypical group did not uncover any obvious differences between them and more typical ORs. Nonetheless, the pattern of expression suggests that atypical ORs may be non-functional despite the lack of any obvious abnormality in the sequence analyses.

The olfactory G protein-coupled receptor (Olfr-78/OR51E2) modulates the intestinal response to colitis.

Olfactory receptor-78 (Olfr-78) is a recently identified G protein-coupled receptor activated by short-chain fatty acids acetate and propionate. A suggested role for this receptor exists in the prostate where it may influence chronic inflammatory response leading to intraepithelial neoplasia. Olfr-78 has also been shown to be expressed in mouse colon. Short-chain fatty acids and their receptors are well known to modulate inflammation in the gut. Considering this possibility, we first explored if colitis regulated Olfr-78 expression in the gut, where we observed a significant reduction in the expression of Olfr-78 transcript in mouse models of dextran sodium sulfate (DSS)- and 2,4,6-trinitrobenzenesulfonic acid (TNBS)-induced colitis. To more directly test this, mice deficient in Olfr-78 were administered with DSS in water for 7 days and were found to have increased expression of IL-1β and inflammatory signs in colon compared with control mice. Next, we explored the expression of its human counterpart olfactory receptor family 51, subfamily E, member 2 (OR51E2) in human intestinal samples and observed that it was in fact also expressed in human colon samples. RNA sequence analysis revealed significant changes in the genes involved in infection, immunity, inflammation, and colorectal cancer between wild-type and Olfr-78 knockout mice. Collectively, our findings show that Olfr-78 is highly expressed in colon and downregulated in DSS- and TNBS-induced colitis, and DSS-treated Olfr-78 null mice had increased colonic expression of cytokine RNA levels, suggesting a potential role for this receptor in intestinal inflammation. Future investigations are needed to understand how Olfr-78/OR51E2 in both mouse and human intestine modulates gastrointestinal pathophysiology.

Optimisation of cancer classification by machine learning generates an enriched list of candidate drug targets and biomarkers.

The Cancer Genome Atlas has provided expression values of 18 015 genes for different cancer types. Studies on the classification of cancers by machine learning algorithms have used different data and methods, which makes it difficult to compare their performance. It is unclear, which algorithm performs best and if maximum levels of accuracy have been obtained. In this study, we aimed to optimise the diagnosis of cancer by comparing the performance of five algorithms using the same data, and by identifying the smallest possible number of differentiator genes. Classification accuracies of five algorithms of cancer type and primary site were determined using a gene expression dataset of 5629 samples and a dataset of 9144 samples, respectively. When trained with sample sets ranging from 16 718 to 40 genes, Random Forest (RF), Gradient Boosting Machine (GBM), and Neural Network (NN) consistently achieved 100% or near 100% accuracy in the classification of both cancer type and primary site. Reduction of training sets to the 40 highest-ranked genes resulted in 78-fold and 45-fold faster processing times for RF and GBM, respectively. The olfactory receptor family, keratin associated proteins, and defensin beta family were among the highest ranked genes. The ensemble and NN algorithms were the most accurate at distinguishing between cancer types and primary sites, whereas KNN was the fastest. Training sets can be reduced to the 40 highest-ranked differentiator genes without any significant loss of accuracy, amongst which there are potential drug targets and biomarkers.

The Olfactory Receptor Family 2, Subfamily T, Member 6 (OR2T6) Is Involved in Breast Cancer Progression via Initiating Epithelial-Mesenchymal Transition and MAPK/ERK Pathway.

Breast cancer is the most common female malignancy worldwide, however its molecular pathogenesis still needs in-depth investigation. Here we first revealed that the olfactory receptor family 2, subfamily T, member 6 (OR2T6) was significantly over-expressed in breast cancer tissues compared with normal breast tissues. OR2T6 expression was tightly correlated with higher TNM staging, positive lymph node metastasis, and associated with poorer patients' overall and disease-free survival. And OR2T6 enhanced the proliferation, invasion, and migration ability of breast cancer cell lines in vitro (MCF-7 and MDA-MD-231). Mechanically, it promoted the expression of mesenchymal markers (Vimentin, N-cadherin, and β-catenin) while inhibited E-cadherin expression, suggesting that OR2T6 played a key role in the regulation of epithelial-mesenchymal transition (EMT) process. Moreover, the human gene expression microarray clarified that MAPK/ERK pathway could be initiated by OR2T6 at mRNA level, which was further confirmed at protein level by western blot analysis. Thus, we concluded that OR2T6, as a novel oncogene, contributed to the progression of breast carcinoma by the initiation of EMT and MAPK/ERK pathway.

Human Cytomegalovirus Cell Tropism and Host Cell Receptors.

In the 1970s–1980s, a striking increase in the number of disseminated human cytomegalovirus (HCMV) infections occurred in immunosuppressed patient populations. Autopsy findings documented the in vivo disseminated infection (besides fibroblasts) of epithelial cells, endothelial cells, and polymorphonuclear leukocytes. As a result, multiple diagnostic assays, such as quantification of HCMV antigenemia (pp65), viremia (infectious virus), and DNAemia (HCMV DNA) in patient blood, were developed. In vitro experiments showed that only low passage or endothelial cell-passaged clinical isolates, and not laboratory-adapted strains, could reproduce both HCMV leuko- and endothelial cell-tropism, which were found through genetic analysis to require the three viral genes UL128, UL130, and UL131 of the HCMV UL128 locus (UL128L). Products of this locus, together with gH/gL, were shown to form the gH/gL/pUL128L pentamer complex (PC) required for infection of epithelial cells/endothelial cells, whereas gH/gL and gO form the gH/gL/gO trimer complex (TC) required for infection of all cell types. In 2016, following previous work, a receptor for the TC that mediates entry into fibroblasts was identified as PDGFRα, while in 2018, a receptor for the PC that mediates entry into endothelial/epithelial cells was identified as neuropilin2 (Nrp2). Furthermore, the olfactory receptor family member OR14I1 was recently identified as a possible additional receptor for the PC in epithelial cells. Thus, current data support two models of viral entry: (i) in fibroblasts, following interaction of PDGFRα with TC, the latter activates gB to fuse the virus envelope with the cell membrane, whereas (ii) in epithelial cells/endothelial cells, interaction of Nrp2 (and OR14I1) with PC promotes endocytosis of virus particles, followed by gB activation by gH/gL/gO (or gH/gL) and final low-pH entry into the cell.

Analysis of a Protein Network Related to Copy Number Variations in Autism Spectrum Disorder.

Autism spectrum disorder (ASD) is a neurodevelopmental disorder, with strong genetic influences as evidenced by its high heritability. Submicroscopic variations (ranging from one kilobase to several megabases) in DNA, called copy number variations (CNVs), have been associated with psychiatric diseases, including ASD. We aimed to identify CNVs in children diagnosed with idiopathic ASD. We used microarray-based comparative genomic hybridization analysis to detect the CNVs, and bioinformatic tools to evaluate their pathogenic potential, based on predicted functional aspects. Using combined cytogenetic and bioinformatic tools, we identified an autism network of genes/proteins related to the CNVs. Among the 40 children analyzed, we found 14 potentially pathogenic CNVs, including those previously associated with ASD (located at 16p11.2, 15q11.2, and 7p21 regions). We suggest that the most relevant biological process and functional attributes involve olfactory receptors. The CNV-related autism network comprised 90 proteins and 754 nodes and indicated the family of olfactory receptors as a significant pathway in ASD. Olfactory receptors were previously associated with neurologic diseases, and they are possibly related to cognition. This integrative analysis that combines cytogenetics and bioinformatics is a promising approach to understand complex conditions such as ASD.

Long noncoding RNA OR3A4 promotes cisplatin resistance of non-small cell lung cancer by upregulating CDK1.

Numerous studies have proved that long non-coding RNAs (lncRNAs) have an important role in malignant tumors, including non-small cell lung cancer (NSCLC). LncRNA olfactory receptor family 3 subfamily A member 4 (OR3A4) was explored to identify how it functions in resistance of NSCLC patients to cisplatin. Real Time-quantitative Polymerase Chain Reaction (RT-qPCR) was utilized to detect OR3A4 expression in NSCLC patients. Then, we conducted Cell Counting Kit-8 (CCK-8) assay and flow cytometric analysis to detect the function of OR3A4 on the resistance of NSCLC cells to cisplatin. Furthermore, the potential mechanism was explored by mechanism assays. Compared with OR3A4 expression of paired A549 cells, OR3A4 expression of A549/DDP cells was higher. Moreover, the functional assay showed that after OR3A4 was silenced in A549/DDP cells, cell cycle arrest and cell apoptosis was induced, and resistance to cisplatin was reversed. Furthermore, it was found that CDK1 expression was suppressed in A549/DDP cells by knockdown of OR3A4. The present work suggests that OR3A4 participates in regulating cell cycle, cell apoptosis of NSCLC cells and the resistance to cisplatin via upregulating CDK1, indicating that OR3A4 could be identified as a potential therapeutic target for NSCLC patients.

Olfactory Receptor Family 7 Subfamily C Member 1 Expression in T‐cell Acute Lymphoblastic leukemia Identifies a Potential Stem Cell Sub‐population

Cancer stem cells (CSCs) are thought to be a self‐renewing population that is difficult to kill during standard chemotherapy due to the capacity of the cells for self‐renewal and multidrug resistance. Our lab studies T‐cell acute lymphoblastic leukemia (T‐ALL), which is an aggressive form of leukemia. T‐ALL cells, which can hide from chemotherapeutic treatment regimens within the central nervous system ( CNS), use different chemokine and adhesion receptors to invade the CNS; entry into the CNS contributes to the aggressiveness of the disease. Therefore, migration into the CNS necessitates the use of aggressive treatments such as cranial irradiation and intensified intrathecal chemotherapy, which causes neurocognitive deficits, endocrine disorders, and growth impairment. A recent study showed that the ectopic expression of Olfactory Receptor Family 7 Subfamily C Member 1 (OR7C1) correlates with expression of stem cell markers including SOX2, POU5F1, and LGR5. These stem‐cell markers correlate with decreased survival rates, implicating the expression of these stem cells in chemo‐resistant cancers. Therefore, we hypothesized that the expression of these stem cell markers in T‐ALL cell lines would contribute to the aggressiveness of the disease. Using flow cytometry, we found approximately 1% of HuT78, adult human T‐ALL cells, express OR7C1. Furthermore, while we were able to detect OR7C1 protein expression in HuT78 cells through both Western blot and RT‐PCR, we found that peripheral blood mononuclear cells (PBMCs) lack OR7C1. Currently, we are determining if the expression of OR7C1 leads to the expression of stem cell transcription factors in HuT78, CCRF‐CEM pediatric T cell lines, and PBMCs. These findings will allow us to determine the prognostic significance of OR7C1 in the progression of T‐ALL.Support or Funding InformationNSF award DUE‐1565063This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Olfactory Receptor Family 7 Subfamily C Member 1 as a potential prognostic marker for pediatric T‐cell acute lymphoblastic leukemia patients

A recent study showed that self‐renewing colorectal cancer‐stem cells/cancer‐initiating cells ectopically express the olfactory receptor family 7 subfamily C member 1 (OR7C1). OR7C1, which is a G protein‐coupled receptor (GPCR) was associated with the expression of stem‐cell markers and decreased survival of colon cancer patients. We study T‐cell acute lymphoblastic leukemia (T‐ALL), a neoplasm of immature T‐cell precursors that predominately affect children with an incidence of ~20% of the overall acute lymphoblastic leukemia (ALL) cases. In a screen of 9 pediatric T‐ALL patients, we identified a single nucleotide polymorphism (SNP) in the OR7C1 gene in isolated T‐cells from all 9 patients with T‐ALL that was not present in control T‐cells. Based on published 3D structures of GPCRs we have used in silico modeling to predict the structural effects of the OR7C1 point mutation located in the second extracellular loop, which we expect will regulate downstream signaling. We hypothesize that the SNP form of OR7C1 contributes to the proliferation and aggressiveness of T‐ALL. We identified OR7C1 expression in human T‐ALL cell lines by reverse transcription PCR and western blot analysis with no expression in control peripheral blood mononuclear cells. Sequencing of amplified DNA from T‐ALL cell lines determined the same OR7C1 SNP in two of the human T‐ALL cell lines that we observed in pediatric T‐ALL patients. Using an antibody to OR7C1, we have isolated OR7C1 expressing cells by fluorescence‐activated cell sorting in T‐ALL cell line, HuT78. Currently, we are determining the stemness characteristics of our enriched OR7C1 expressing HuT78 population with the aim of defining the role of OR7C1 in T‐ALL cell proliferation and invasiveness.Support or Funding InformationResearch reported in this poster was supported by the National Institute of General Medical Sciences of the National Institutes of Health under linked Award Numbers SC1GM111172, RL5GM118969, TL4GM118971, UL1GM118970, and 5G12MD007592.The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Aedes aegypti Mosquitoes Detect Acidic Volatiles Found in Human Odor Using the IR8a Pathway

Mosquitoes use olfaction as a primary means of detecting their hosts. Previously, the functional ablation of a family of Aedes aegypti olfactory receptors, the odorant receptors (ORs), was not sufficient to reduce host seeking in the presence of carbon dioxide (CO2). This suggests the olfactory receptors that remain, such as the ionotropic receptors (IRs), could play a significant role in host detection. To test this, we disrupted the Ir8a co-receptor in Ae. aegypti using CRISPR/Cas9. We found that Ir8a mutant female mosquitoes are not attracted to lactic acid, a behaviorally active component of human sweat, and they lack odor-evoked responses to acidic volatiles. The loss of Ir8a reduces mosquito attraction to humans and their odor. We show that the CO2-detection pathway is necessary but not sufficient for IR8a to detect human odor. Our study reveals that the IR8a pathway is crucial for an anthropophilic vector mosquito to effectively seek hosts. VIDEO ABSTRACT.

OR14I1 is a receptor for the human cytomegalovirus pentameric complex and defines viral epithelial cell tropism

A human cytomegalovirus (HCMV) pentameric glycoprotein complex (PC), gH-gL-UL128-UL130-UL131A, is necessary for viral infection of clinically relevant cell types, including epithelial cells, which are important for interhost transmission and disease. We performed genome-wide CRISPR/Cas9 screens of different cell types in parallel to identify host genes specifically required for HCMV infection of epithelial cells. This effort identified a multipass membrane protein, OR14I1, as a receptor for HCMV infection. This olfactory receptor family member is required for HCMV attachment, entry, and infection of epithelial cells and is dependent on the presence of viral PC. OR14I1 is required for AKT activation and mediates endocytosis entry of HCMV. We further found that HCMV infection of epithelial cells is blocked by a synthetic OR14I1 peptide and inhibitors of adenylate cyclase and protein kinase A (PKA) signaling. Identification of OR14I1 as a PC-dependent HCMV host receptor associated with epithelial tropism and the role of the adenylate cyclase/PKA/AKT-mediated signaling pathway in HCMV infection reveal previously unappreciated targets for the development of vaccines and antiviral therapies.

Putative Receptors Underpinning l-Lactate Signalling in Locus Coeruleus

The importance of astrocytic l-lactate (LL) for normal functioning of neural circuits such as those regulating learning/memory, sleep/wake state, autonomic homeostasis, or emotional behaviour is being increasingly recognised. l-Lactate can act on neurones as a metabolic or redox substrate, but transmembrane receptor targets are also emerging. A comparative review of the hydroxy-carboxylic acid receptor (HCA1, formerly known as GPR81), Olfactory Receptor Family 51 Subfamily E Member 2 (OR51E2), and orphan receptor GPR4 highlights differences in their LL sensitivity, pharmacology, intracellular coupling, and localisation in the brain. In addition, a putative Gs-coupled receptor on noradrenergic neurones, LLRx, which we previously postulated, remains to be identified. Next-generation sequencing revealed several orphan receptors expressed in locus coeruleus neurones. Screening of a selection of these suggests additional LL-sensitive receptors: GPR180 which inhibits and GPR137 which activates intracellular cyclic AMP signalling in response to LL in a heterologous expression system. To further characterise binding of LL at LLRx, we carried out a structure–activity relationship study which demonstrates that carboxyl and 2-hydroxyl moieties of LL are essential for triggering d-lactate-sensitive noradrenaline release in locus coeruleus, and that the size of the LL binding pocket is limited towards the methyl group position. The evidence accumulating to date suggests that LL acts via multiple receptor targets to modulate distinct brain functions.

Aedes Aegypti Mosquitoes Detect Acidic Volatiles in Human Odor Using the IR8a Pathway

Mosquitoes use olfaction as a primary means of detecting their hosts. Previously, the genetic ablation of a family of Aedes aegypti olfactory receptors, the Odorant Receptors (ORs), was not sufficient to reduce host-seeking in the presence of carbon dioxide (CO2). This suggests the olfactory receptors that remain, such as the Ionotropic Receptors (IRs), could play a significant role in host detection. To test this, we disrupted the Ir8a co-receptor in Ae. aegypti using CRISPR/Cas9. Ir8a mutant female mosquitoes are not attracted to lactic acid, a behaviorally active component of human odor, and lack odor-evoked responses to acidic volatiles. The loss of Ir8a reduces mosquito attraction to humans and their odor. We show that the CO2-detection pathway is necessary but not sufficient for IR8a to detect human odor. Our study reveals that the IR8a pathway is crucial for an anthropophilic vector mosquito to effectively seek hosts.

The Two Main Olfactory Receptor Families in Drosophila, ORs and IRs: A Comparative Approach.

Most insect species rely on the detection of olfactory cues for critical behaviors for the survival of the species, e.g., finding food, suitable mates and appropriate egg-laying sites. Although insects show a diverse array of molecular receptors dedicated to the detection of sensory cues, two main types of molecular receptors have been described as responsible for olfactory reception in Drosophila, the odorant receptors (ORs) and the ionotropic receptors (IRs). Although both receptor families share the role of being the first chemosensors in the insect olfactory system, they show distinct evolutionary origins and several distinct structural and functional characteristics. While ORs are seven-transmembrane-domain receptor proteins, IRs are related to the ionotropic glutamate receptor (iGluR) family. Both types of receptors are expressed on the olfactory sensory neurons (OSNs) of the main olfactory organ, the antenna, but they are housed in different types of sensilla, IRs in coeloconic sensilla and ORs in basiconic and trichoid sensilla. More importantly, from the functional point of view, they display different odorant specificity profiles. Research advances in the last decade have improved our understanding of the molecular basis, evolution and functional roles of these two families, but there are still controversies and unsolved key questions that remain to be answered. Here, we present an updated review on the advances of the genetic basis, evolution, structure, functional response and regulation of both types of chemosensory receptors. We use a comparative approach to highlight the similarities and differences among them. Moreover, we will discuss major open questions in the field of olfactory reception in insects. A comprehensive analysis of the structural and functional convergence and divergence of both types of receptors will help in elucidating the molecular basis of the function and regulation of chemoreception in insects.

Clinical significance of expression of olfactory receptor family 2 subfamily W member 3 in human pancreatic cancer

Clinical significance of expression of olfactory receptor family 2 subfamily W member 3 in human pancreatic cancer

Overlapping but distinct topology for zebrafish V2R-like olfactory receptors reminiscent of odorant receptor spatial expression zones

BackgroundThe sense of smell is unrivaled in terms of molecular complexity of its input channels. Even zebrafish, a model vertebrate system in many research fields including olfaction, possesses several hundred different olfactory receptor genes, organized in four different gene families. For one of these families, the initially discovered odorant receptors proper, segregation of expression into distinct spatial subdomains within a common sensory surface has been observed both in teleost fish and in mammals. However, for the remaining three families, little to nothing was known about their spatial coding logic. Here we wished to investigate, whether the principle of spatial segregation observed for odorant receptors extends to another olfactory receptor family, the V2R-related OlfC genes. Furthermore we thought to examine, how expression of OlfC genes is integrated into expression zones of odorant receptor genes, which in fish share a single sensory surface with OlfC genes.ResultsTo select representative genes, we performed a comprehensive phylogenetic study of the zebrafish OlfC family, which identified a novel OlfC gene, reduced the number of pseudogenes to 1, and brought the total family size to 60 intact OlfC receptors. We analyzed the spatial pattern of OlfC-expressing cells for seven representative receptors in three dimensions (height within the epithelial layer, horizontal distance from the center of the olfactory organ, and height within the olfactory organ). We report non-random distributions of labeled neurons for all OlfC genes analysed. Distributions for sparsely expressed OlfC genes are significantly different from each other in nearly all cases, broad overlap notwithstanding. For two of the three coordinates analyzed, OlfC expression zones are intercalated with those of odorant receptor zones, whereas in the third dimension some segregation is observed.ConclusionOur results show that V2R-related OlfC genes follow the same spatial logic of expression as odorant receptors and their expression zones intermingle with those of odorant receptor genes. Thus, distinctly different expression zones for individual receptor genes constitute a general feature shared by teleost and tetrapod V2R/OlfC and odorant receptor families alike.

Enormous expansion of the chemosensory gene repertoire in the omnivorous German cockroach Blattella germanica.

The acquisition of genome sequences from a wide range of insects and other arthropods has revealed a broad positive correlation between the complexity of their chemical ecology and the size of their chemosensory gene repertoire. The German cockroach Blattella germanica is an extreme omnivore and has the largest chemosensory gene repertoire known for an arthropod, exceeding even the highly polyphagous spider mite Tetranychus urticae. While the Odorant Receptor family is not particularly large, with 123 genes potentially encoding 134 receptors (105 intact), the Gustatory Receptor family is greatly expanded to 431 genes potentially encoding 545 receptors (483 intact), the largest known for insects and second only to the spider mite. The Ionotropic Receptor family of olfactory and gustatory receptors is vastly expanded to at least 897 genes (604 intact), the largest size known in arthropods, far surpassing the 150 known from the dampwood termite Zootermopsis nevadensis. Commensurately, the Odorant Binding Protein family is expanded to the largest known for insects at 109 genes (all intact). Comparison with the far more specialized, but phylogenetically related termite, within the Dictyoptera, reveals considerable gene losses from the termite, and massive species‐specific gene expansions in the cockroach. The cockroach has lost function of 11%–41% of these three chemoreceptor gene families to pseudogenization, and most of these are young events, implying rapid turnover of genes along with these major expansions, presumably in response to changes in its chemical ecology.

Homoeologous Recombination of the V1r1-V1r2 Gene Cluster of Pheromone Receptors in an Allotetraploid Lineage of Teleosts.

In contrast to other olfactory receptor families that exhibit frequent lineage-specific expansions, the vomeronasal type 1 receptor (V1R) family exhibits a canonical six-member repertoire in teleosts. V1r1 and V1r2 are present in no more than one copy in all examined teleosts, including salmons, which are ancient polyploids, implying strict evolutionary constraints. However, recent polyploids have not been examined. Here, we identified a young allotetraploid lineage of weatherfishes and investigated their V1r1-V1r2 cluster. We found a novel pattern that the parental V1r1-V1r2 clusters had recombined in the tetraploid genome and that the recombinant was nearly fixed in the tetraploid population. Subsequent analyses suggested strong selective pressure, for both a new combination of paralogs and homogeneity among gene duplicates, acting on the V1r1-V1r2 pair.