The role of Acj6 in odor receptor gene choice

Lei Bai, Aaron Goldman, John Carlson. MCDB, Yale University, New Haven, CT.

The selected expression of odor receptor (Or) genes underlies the odor-specificities of olfactory receptor neurons. The Or gene family in Drosophila consists of 60 members, most of which are expressed in either the larval olfactory organ or one of the adult olfactory organs in a non-overlapping pattern. Little is known about how individual neurons select which Or genes to express. Abnormal chemosensory jump 6, which encodes a POU-domain transcription factor, has been implicated in this process. Physiological analysis of individual olfactory neurons shows that in acj6 mutants, some neurons appear normal, some lose response to all tested odors, and some acquire a different response profile. We characterized the expression of a subset of Or genes in the adult acj6 mutants. Of the Or genes that normally are expressed in neurons of the maxillary palp or the large basiconic sensilla of the antenna, a majority are not expressed in acj6 mutants, resulting in the loss of odor sensitivities of many neurons. A subset of neurons, however, chooses to express an odor receptor that normally is expressed in larval, but not adult, olfactory neurons. The switch in receptor expression accounts for the change in the odor response profile previously characterized. Thus Acj6 acts positively on some Or genes, and negatively on another. Using an in vitro binding selection assay, we characterized the binding specificities of Acj6 to short oligonucleotides. Based on the results, we identified predicted Acj6 binding sites in the promoters of a subset of Or genes. Mutation of some of these sites greatly reduces reporter gene expression driven by Or gene promoters, suggesting that Acj6 regulates a subset of Or genes by directly binding to their promoter sequences.

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