A Novel Family of Divergent Seven-Transmembrane Proteins

Abstract

Although insects have proven to be valuable models for exploring the function, organization, and development of the olfactory system, the receptor molecules that bind odors have not been identified in any insect. We have developed a novel search algorithm, used it to search the Drosophila genomic sequence database, and identified a large multigene family encoding seven transmembrane domain proteins that are expressed in olfactory organs. We show that expression is restricted to subsets of olfactory receptor neurons (ORNs) for a number of these genes. Different members of the family initiate expression at different times during antennal development. Some of the genes are not expressed in a mutant of the Acj6 POU-domain transcription factor, a mutant in which a subset of ORNs show abnormal odorant specificities.

Target neuron prespecification in the olfactory map of Drosophila

“…In mice, ORNs seem to be genetically programmed to project to speci®c glomeruli, instructed by the receptors that they express 11 ; indeed, this convergence seems to be independent of the presence of the target neurons of the olfactory bulb 12 . Although analogous experiments have not been reported in¯ies, ORNs expressing a particular receptor reside in stereotypic and discrete zones of the antennae and maxillary palpsÐthe¯y's olfactory appendages 2,6,7 .…”

“…2a). About 1,300 ORNs expressing 40±60 different receptors 2,6,7 project their axons to 40±50 individually identi®able glomeruli of the antennal lobe 8 (equivalent to the mammalian olfactory bulb 9 ). Information leaves the antennal lobe through an estimated 150 projection neurons (equivalent to mammalian mitral/tufted cells), whose cell bodies are located at the periphery of the antennal lobe 4,10 (Fig.…”

Generation and modulation of chemosensory behaviors in C. elegans

“…Given the critical importance of chemosensation for the worm's survival, it is perhaps not surprising that nearly 10% of the C. elegans genome is devoted to encoding predicted chemosensory receptors (CRs), a current total of ∼1,500 molecules [58, [116][117][118]. In comparison, the Drosophila genome is predicted to encode ∼62 olfactory and ∼68 gustatory receptors [119][120][121][122][123], whereas the mouse genome encodes ∼1,200 olfactory and 38 gustatory GPCRs [93,94,[124][125][126][127][128]. Although the expression patterns of only a handful of CR genes have been examined [58,129], it is clear that in stark contrast to the vertebrate or Drosophila olfactory systems, each chemosensory neuron in C. elegans expresses multiple CR genes, perhaps as many as 20 per neuron type (Fig.…”

A Systematic Analysis of Drosophila Gustatory Receptor Gene Expression in Abdominal Neurons which Project to the Central Nervous System

“…Drosophila melanogaster provides a relatively easily manipulated genetic system to study chemosensation. Molecular studies of Drosophila chemosensation were initiated upon molecular identification of the odorant and gustatory receptors (Clyne et al, 1999;2000;Vosshall et al, 1999).…”