Despite increasing knowledge about dimerization of G-protein-coupled receptors, nothing is known about dimerization in the largest subfamily, odorant receptors. Using a combination of biochemical and electrophysiological approaches, we demonstrate here that odorant receptors can dimerize. DOR83b, an odorant receptor that is ubiquitously expressed in olfactory neurons from Drosophila melanogaster and highly conserved among insect species, forms heterodimeric complexes with other odorant-receptor proteins, which strongly increases their functionality.

The neural basis of sexual orientation in Drosophila was studied by the production of males with regionally feminized brains. Such flies express the female form of the sex determination gene transformer in a limited number of neurons under the control of GAL4 enhancer trap inserts. This method facilitated the creation of lines with a stable pattern of feminization. In tests of sexual preferences, flies that were feminized in a portion of the antennal lobes or in a subset of the corpora pedunculata (mushroom bodies) courted both males and females. These two brain structures, both of which are involved in olfactory processing, may function in the recognition of sex-specific pheromones, in the control of sex-specific behaviors, or both.

The Drosophila ebony mutation (Bridges and Morgan, [1923] Publs Carnegie Inst Wash 327:50) reveals a pleiotropic phenotype with cuticular and behavioral defects. To understand Ebony function in the nervous system, particularly in transmission of the visual signal, it is essential to know the cell type and temporal characteristics of its expression throughout development. Therefore, we raised an antiserum against an Ebony peptide to detect the protein in whole-mount and slice preparations of Drosophila. Attention was focused on ebony expression in the adult optic neuropiles of the fly. Colocalization of Ebony with neuronal or glial cell markers in frozen sections showed non-neuronal expression of ebony in the lamina and medulla neuropiles. Furthermore, colocalization with glial cell markers demonstrated glial expression of ebony in epithelial glia of the lamina and neuropile glia of the distal medulla. This finding was confirmed for the lamina epithelial glia by electron microscopic examination of immunolabeling by using the diaminobenzidine method. These glia have in common that they match the two sites of histamine release from the compound eye's photoreceptors. Possible ways in which the biochemical activity of Ebony might function with respect to histamine release are considered.

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