A genetic platform for functionally profiling odorant receptors in olfactory cilia ex vivo.

The molecular basis for odor perception in humans remains enigmatic because of the difficulty in studying odorant receptors (ORs) outside their native environment. Efforts toward OR expression and functional profiling have been met with limited success because of the poor efficiency of their cell surface expression in vitro. Structures protruding from the surface of olfactory sensory neurons called cilia contain all of the components of the olfactory signal transduction machinery and can be placed in an ex vivo plate assay to rapidly measure odor-specific responses.

Danger perception and stress response through an olfactory sensor for the bacterial metabolite hydrogen sulfide.

The olfactory system serves a critical function as a danger detection system to trigger defense responses essential for survival. The cellular and molecular mechanisms that drive such defenses in mammals are incompletely understood. Here, we have discovered an ultrasensitive olfactory sensor for the highly poisonous bacterial metabolite hydrogen sulfide (HS) in mice.

A Sensor for Low Environmental Oxygen in the Mouse Main Olfactory Epithelium.

Sensing the level of oxygen in the external and internal environments is essential for survival. Organisms have evolved multiple mechanisms to sense oxygen. No function in oxygen sensing has been attributed to any mammalian olfactory system.

Expression of homeobox genes in the mouse olfactory epithelium.

Homeobox genes constitute a large family of genes widely studied because of their role in the establishment of the body pattern. However, they are also involved in many other events during development and adulthood. The main olfactory epithelium (MOE) is an excellent model to study neurogenesis in the adult nervous system.

Hierarchical deconstruction of mouse olfactory sensory neurons: from whole mucosa to single-cell RNA-seq.

The mouse olfactory mucosa is a complex chemosensory tissue composed of multiple cell types, neuronal and non-neuronal. We have here applied RNA-seq hierarchically, in three steps of decreasing cellular heterogeneity: starting with crude tissue samples dissected from the nose, proceeding to flow-cytometrically sorted pools of mature olfactory sensory neurons (OSNs), and finally arriving at single mature OSNs. We show that 98.

Trpc2-expressing sensory neurons in the mouse main olfactory epithelium of type B express the soluble guanylate cyclase Gucy1b2.

Chemoreception in the mouse olfactory system occurs primarily at two chemosensory epithelia in the nasal cavity: the main olfactory epithelium (MOE) and the vomeronasal epithelium. The canonical chemosensory neurons in the MOE, the olfactory sensory neurons (OSNs), express the odorant receptor (OR) gene repertoire, and depend on Adcy3 and Cnga2 for chemosensory signal transduction. The canonical chemosensory neurons in the vomeronasal epithelium, the vomeronasal sensory neurons (VSNs), express two unrelated vomeronasal receptor (VR) gene repertoires, and involve Trpc2 for chemosensory signal transduction.

Trpc2-expressing sensory neurons in the main olfactory epithelium of the mouse.

The mouse olfactory system contains two distinct chemosensory epithelia, the main olfactory epithelium (MOE) and the vomeronasal epithelium (VNE). Their sensory neurons express odorant receptor genes and vomeronasal receptor genes, respectively, and differ fundamentally in their signal transduction pathways. Genes required for chemosensory transduction are the cyclic nucleotide-gated channel subunit Cnga2 and the transient receptor potential cation channel Trpc2, respectively.

The β2-adrenergic receptor as a surrogate odorant receptor in mouse olfactory sensory neurons.

In the mouse, mature olfactory sensory neurons (OSNs) express one allele of one of the ~1200 odorant receptor (OR) genes, which encode G-protein coupled receptors (GPCRs). Axons of OSNs that express the same OR coalesce into homogeneous glomeruli at conserved positions in the olfactory bulb. ORs are involved in OR gene choice and OSN axonal wiring, but the mechanisms remain poorly understood.

Local and cis effects of the H element on expression of odorant receptor genes in mouse.

From the approximately 1,200 odorant receptor (OR) genes in the mouse genome, an olfactory sensory neuron is thought to express only one gene. The mechanisms of OR gene choice are not understood. A 2.

Differential impact of Lhx2 deficiency on expression of class I and class II odorant receptor genes in mouse.

Odorant receptor (OR) genes can be classified into two types: fish-like class I OR genes and mammalian-specific class II OR genes. We have previously shown that Lhx2, a LIM-homeodomain protein, binds to the homeodomain site in the promoter region of mouse M71, a class II OR, and that a knockout mutation in Lhx2 precludes expression of all tested class II OR genes including M71. Here, we report that most class I OR genes, which are expressed in a dorsal region of the olfactory epithelium, are still expressed in Lhx2-deficient embryos.

Odorant receptor map in the mouse olfactory bulb: in vivo sensitivity and specificity of receptor-defined glomeruli.

Odorant identity is represented in the olfactory bulb (OB) by the glomerular activity pattern, which reflects a combination of activated odorant receptors (ORs) in the olfactory epithelium. To elucidate this neuronal circuit at the molecular level, we established a functional OR identification strategy based on glomerular activity by combining in vivo Ca(2+) imaging, retrograde dye labeling, and single-cell RT-PCR. Spatial and functional mapping of OR-defined glomeruli revealed that the glomerular positional relationship varied considerably between individual animals, resulting in different OR maps in the OB.

Development and topography of the lateral olfactory tract in the mouse: imaging by genetically encoded and injected fluorescent markers.

In mammals, conventional odorants are detected by OSNs located in the main olfactory epithelium of the nose. These neurons project their axons to glomeruli, which are specialized structures of neuropil in the olfactory bulb. Within glomeruli, axons synapse onto dendrites of projection neurons, the mitral and tufted (M/T) cells.

The Grueneberg ganglion of the mouse projects axons to glomeruli in the olfactory bulb.

First described in 1973, the Grueneberg ganglion (GG) is an arrow-shaped neuronal structure at the anterior end of the nasal cavity. It lines both sides of the nasal septum, within the nasal vestibule, close to the opening of the naris. The functions of the GG and the pattern of projections to the brain are not known.

Protocols for two- and three-color fluorescent RNA in situ hybridization of the main and accessory olfactory epithelia in mouse.

The main and accessory olfactory epithelia of the mouse are composed of many cell populations. Each sensory neuron is thought to express one allele of one of the approximately 1000 odorant or approximately 300 vomeronasal receptor genes. Sensory neurons die and are replaced by new neurons that differentiate from precursor cells throughout the lifetime of the individual.

Olfactory receptor antagonism between odorants.

The detection of thousands of volatile odorants is mediated by several hundreds of different G protein-coupled olfactory receptors (ORs). The main strategy in encoding odorant identities is a combinatorial receptor code scheme in that different odorants are recognized by different sets of ORs. Despite increasing information on agonist-OR combinations, little is known about the antagonism of ORs in the mammalian olfactory system.

In situ Ca2+ imaging of odor responses in a coronal olfactory epithelium slice.

An in situ Ca2+ -imaging technique was adopted to monitor odorant responses of more than several hundreds of neurons simultaneously in an intact coronal slice of the mouse olfactory epithelium. The sensitivity and resolution of the slice Ca2+ -imaging were high enough to distinguish between olfactory receptor neurons with threshold concentrations in a one-order difference for a particular odorant at the single-cell level. Increasing odorant concentrations resulted in increases in the numbers of odorant-responsive neurons, which were visualized in situ in the coronal slice.