Olfactory receptor neuron

An olfactory receptor neuron (ORN), also called an olfactory sensory neuron (OSN), is a sensory neuron within the olfactory system. Structure Humans have between 10 and 20 million olfactory receptor neurons (ORNs). In vertebrates, ORNs are bipolar neurons with dendrites facing the external surface of the cribriform plate with axons that pass through the cribriform foramina with terminal end at olfactory bulbs. The ORNs are located in the olfactory epithelium in the nasal cavity. The cell bodies of the ORNs are distributed among all three of the stratified layers of the olfactory epithelium. Many tiny hair-like non-motile cilia protrude from the olfactory receptor cell's dendrites. The dendrites extend to the olfactory epithelial surface and each ends in a dendritic knob from which around 20 to 35 cilia protrude. The cilia have a length of up to 100 micrometres and with the cilia from other dendrites form a meshwork in the olfactory mucus. The surface of the cilia is c

Dual activities of odorants on olfactory and nuclear hormone receptors

Olivia Baud, Sylvain Etter, Horst Pick, Ralf Schmauder, Horst Vogel

We have screened an odorant compound library and discovered molecules acting as chemical signals that specifically activate both G-protein-coupled olfactory receptors (ORs) on the cell surface of olfactory sensory neurons and the human nuclear estrogen receptor alpha (ER) involved in transcriptional regulation of cellular differentiation and proliferation in a wide variety of tissues. Hence, these apparent dual active odorants induce distinct signal transduction pathways at different subcellular localizations, which affect both neuronal signaling, resulting in odor perception, and the ER-dependent transcriptional control of specific genes. We demonstrate these effects using fluorescence-based in vitro and cellular assays. Among these odorants, we have identified synthetic sandalwood compounds, an important class of molecules used in the fragrance industry. For one estrogenic odorant we have also identified the cognate OR. This prompted us to compare basic molecular recognition principles of odorants on the two structurally and apparent functionally non-related receptors using computational modeling in combination with functional assays. Faced with the increasing evidence that ORs may perform chemosensory functions in a number of tissues outside of the nasal olfactory epithelium, the unraveling of these molecular ligand-receptor interaction principles is of critical importance. In addition the evidence that certain olfactory sensory neurons naturally co-express ORs and ERs may provide a direct functional link between the olfactory and hormonal systems in humans. Our results are therefore useful for defining the structural and functional characteristics of ER-specific odorants and the role of odorant molecules in cellular processes other than olfaction.

American Society for Biochemistry and Molecular Biology2009

Functional Characterization of the Mouse Olfactory Receptor mOR256-17 in Live Cells

Thamani Dahoun

Olfactory receptors (ORs) constitute the largest family of sensory membrane proteins in mammals. They play a key role within the olfactory system to recognize and discriminate a nearly unlimited number of structurally diverse odorant molecules. The molecular basis of OR-mediated odor signal detection and transduction is poorly understood. This is due in part to difficulties in functional expression of ORs at high yield, preventing structural and biophysical studies at the level of the receptor protein. Here we report on the heterologous expression of the mouse receptor mOR256-17 yielding an average of 106 ORs per cell in transiently transfected mammalian cells. For quantification and optimization of OR expression we employed different fluorescent tags. Green fluorescent protein fused to the C-terminus of mOR256-17 allowed quantification of total cellular OR biosynthesis, and posttranslational fluorescence labeling of a 12 amino acid polypeptide sequence at the N-terminus permitted the selective visualization and quantification of ORs at the plasma membrane using cell flow cytometry. The establishment of a mOR256-17-inducible HEK293S-TetO cell line allowed us to determine by fluorescence spectrofluorometry and fluorescence correlation spectroscopy (FCS) the optimal conditions to solubilize the receptor. By screening a large odorant compound library we discovered a new selective spectrum of potent mOR256-17 specific agonists. Furthermore, by using a reporter assay that couples both Gs and Gq proteins after inhibition of adenylate cyclase by the chemical adenylyl cyclase inhibitors 9-(tetrahydro-2-furanyl)-9H-purin-6amine (SQ22536) and after the inhibition of phospholipase C by the chemical inhibitor 1-[6-[[(17β)-3-methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-1H-pyrrole-2,5-dione (U73122), we identified one agonist which induced the inositol 1,4,5-trisphosphate (IP3) transduction pathway. We provided further evidence of the involvement of this second messenger (i) by employing another reporter gene specific to the Gq pathway and (ii) by using electrical impedance spectroscopy. Our attempt to create a FRET fluorophore pair system based on fluorescein arsenical hairpin (FlAsH) labeling and on carrier protein tags to study the receptor conformational changes during activation revealed that modifications in mOR256-17 sequences perturbs the correct receptor folding and prohibits its expression at the plasma membrane. Our study indicated that an essential prerequisite for achieving cell surface expression of mOR256-17 in heterologous cells is the co-expression of the accessory protein RTP1 or its short version RTP1S, which are also expressed by olfactory sensory neurons. Elsewhere, Saito and co-workers have proposed that this protein interacts with OR when the OR is expressed heterologously, but they have not provided evidence to prove the role of RTP1 towards OR. To investigate whether direct physical interactions between mOR256-17 and RTP1 occurs during receptor trafficking to the cell membrane, we labeled mOR256-17 and RTP1 orthogonally using the acyl carrier protein (ACP) and the peptidyl carrier protein (PCP) respectively. In addition, cyan fluorescent protein fused to the N-terminus of RTP1 enabled to study RTP1 biosynthesis in presence and absence of the mOR256-17; here we observed that a large portion of RTP1 remains in the endoplasmic reticulum while the mOR256-17 reaches the Golgi apparatus when it is co-expressed with RTP1S. Furthermore, by using two different RTP1S chimera, we could show that the cytosolic part of RTP1S is important for the mOR256-17 folding and trafficking.

EPFL2013

Functional Characterization of the Mouse Olfactory Receptor mOR256-17 in Live Cells

Thamani Dahoun

EPFL2013

Heterologous Expression and Functional Analysis of Human Odorant Receptor OR17-40 in Olfactory Sensory Neurons

Dual activities of odorants on olfactory and nuclear hormone receptors

Functional Characterization of the Mouse Olfactory Receptor mOR256-17 in Live Cells

Dual activities of odorants on olfactory and nuclear hormone receptors

Heterologous Expression and Functional Analysis of Human Odorant Receptor OR17-40 in Olfactory Sensory Neurons

Functional Characterization of the Mouse Olfactory Receptor mOR256-17 in Live Cells