Molecular genetics of Drosophila olfaction.

The functional organization of the Drosophila olfactory system has been studied using two complementary approaches. (1) A genetic screen has yielded olfactory mutants, of which one, acj6, shows greatly reduced electrical responses of its olfactory organs to all odorants tested except benzaldehyde (odour of almond). This mutant is also defective in olfactory behaviour at the larval stage. It is normal in tests of visual system physiology and behaviour. We aim to determine whether the acj6 gene is expressed on a fraction of the antennal surface. (2) We have carried out an enhancer trap screen for olfactory genes which are expressed on regions of the antennal surface. From a screen of 6400 enhancer trap lines, 12 show expression of a lacZ reporter gene in both larval and adult olfactory organs, but relatively little expression elsewhere. Most lines identify regions of the adult antenna and some show labelling of very small numbers of cells. One line shows sexual dimorphism in its expression pattern and another pattern becomes increasingly restricted with adult age. Several lines also show staining of other chemosensory organs and one also shows staining in the male reproductive tract. We have generated deletions of DNA flanking these enhancer trap insertions to determine whether any of the lines define genes associated with responses to specific sets of odorants.