Repertoire Of Odorant Receptors Research Articles

Seven-transmembrane proteins as odorant and chemosensory receptors.

The olfactory systems of various species solve the challenging problem of general molecular recognition in widely differing ways. Despite this variety, the molecular receptors are invariably G protein-coupled seven-transmembrane proteins, and are encoded by the largest gene families known to exist in a given animal genome. Receptor gene families have been identified in vertebrates and two invertebrate species, the nematode Caenorhabditis elegans and the fruit fly Drosophila melanogaster. The complexity of the odorant receptor repertoire is estimated in mouse and rat at 1000 genes, or 1 percent of the genome, surpassing that of the immunoglobulin and T cell receptor genes combined. Two distinct seven-transmembrane gene families may encode in rodents the chemosensory receptors of the vomeronasal organ, which is specialized in the detection of pheromones. Remarkably, these five receptor families have practically no sequence homology among them. Genetic manipulation experiments in mice imply that vertebrate odorant receptors may fulfill a dual role, also serving as address molecules that guide axons of olfactory sensory neurons to their precise target in the brain.

Molecular biology of odorant receptors in vertebrates.

The initial step in olfactory discrimination involves the interaction of odorous ligands with specific receptors on the surface of olfactory sensory neurons. The foundation for a molecular understanding of odor recognition in vertebrates was provided by the identification of a family of genes encoding putative odorant receptors, by Buck & Axel in 1991. Odorant receptor (OR) genes from the largest gene family in the vertebrate genome. This review summarizes progress over the past seven years. Major new insights are: Olfaction is accomplished in vertebrates by a very large number of receptors; olfactory sensory neurons express a small subset of the OR repertoire; in rat and mouse, axons of neurons expressing the same OR converge onto defined glomeruli in the olfactory bulb.

Coding of olfactory information: Topography of odorant receptor expression in the catfish olfactory epithelium

Discrimination among the vast array of odors requires that the brain discern which of the numerous odorant receptors have been activated. If individual olfactory neurons express only a subset of the odorant receptor repertoire, then the nature of a given odorant can be discerned by identifying which cells have been activated. We performed in situ hybridization experiments demonstrating that individual olfactory neurons express different complements of odorant receptors and are therefore functionally distinct. Thus, a topographic map, defining either the positions of specific neurons in the epithelium or the positions of their projections, may be employed to determine the quality of an olfactory stimulus. Neurons expressing specific receptors appear to be randomly distributed within the olfactory epithelium. These data are consistent with a model in which randomly dispersed olfactory neurons with common receptor specificities project to common glomeruli in the olfactory bulb.