Browsing by Subject "Olfactory receptor"

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Olfaktorische Rezeptoren mit speziellen topographischen Expressionsmustern
(2007) Feistel, Torben; Breer, Heinz
In the present study, olfactory receptors (ORs) featuring special expression patterns in chemosensory subsystems were analyzed. The data showed that out of a repertoire of about 1000 ORs a restricted group (about 50) was not only expressed in the olfactory epithelium but also in the vomeronasal organ, which is generally defined by the expression of characteristic V1R and V2R receptors. The ?ectopically? expressed OR genes represent different receptor families including genes from gene-clusters located on different chromosomes. However, in all individuals the same set of genes seemed to be expressed. The majority of the expressed ORs was present in only a small number of VNO cells, however some were found to be expressed in more than 100 cells. One distinct OR gene (mOR261-6) was expressed in many more cells of female VNOs than in males. The highest number of OR expressing cells was observed in a short postnatal, pre-pubertal period. Cells with mOR18-2-receptors were also found to express a V1R gene. In these cells the OR18-2 gene did not show a mono-allelic expression as compared to expression in the main olfactory system but rather was transcribed from both alleles (bi-allelic) in the vomeronasal neurons. The functional implication of receptor coexpression and bi-allelic OR-expression are unknown. Receptors of the OR37 gene family are exclusively expressed in the olfactory epithelium, in which they are expressed in a special pattern in a central area of the nasal turbinate. Detailed analysis of the spatial distribution of cells equipped with distinct OR37 subtypes revealed that these cells were positioned in specific sub-compartments within this central region. The high number of OR37 expressing cells resulted in the lower number of cells with receptors which are zonally distributed. This implies that cells in a small circumscribed area preferentially expressed OR37 genes. The mechanisms underlying this unique spatial expression pattern of OR37 genes in the olfactory epithelium are currently unknown. A newly generated mouse line was arranged in which even very transient transcription of a OR37 gene is visualized by permanent label in the expressing cells. The examination showed that cells outside of the OR37 cluster did express a OR 37 family member, yet transcription in these cells was rapidly terminated. These results suggest a mechanism which allows an initial transcription of these genes in different areas of the epithelium, but a sustained expression of OR37 genes is restricted exclusively to the central recess of the turbinate. The special features of the OR37 subtypes have led to the hypothesis that these receptors possibly react to chemical compounds relevant for mammalian species. Thus complex mixtures of volatile compounds from the habitat of mice were examined. Electroolfactograms from different regions of the olfactory epithelium showed that the ?head-space? of the embedding from mice cages elicited a stronger response in the central area of the turbinate IIb than in areas outside of this region. Single substances out of this complex mixture induced similar responses in different epithelial recesses. However, 6-hydro-6-methyl-3-heptanon elicited stronger responses within the central OR37 expressing region. This substance is considered to be a mouse pheromone. Taken together, these data on expression and ligand specificity of distinct olfactory receptors suggest, that the vomeronasal organ and the olfactory epithelium although structurally separated chemosensory systems, overlap in their response, spectrum and in their functions, particularly in detecting compounds with biological relevance.