Abnormal Chemosensory Jump 6 Is a Positive Transcriptional Regulator of the Cholinergic Gene Locus in<i>Drosophila</i>Olfactory Neurons

Cholinergic neurons acquire their neurotransmitter phenotype, in part, by expressing the cholinergic gene locus. Previous studies have indicated that the 5′ flanking DNA of the locus contains both positive and negative regulatory elements important for expression in different subsets of cholinergic neurons in <i>Drosophila</i> and other animals. Approximately 300 bases of proximal 5′ flanking DNA control expression in <i>Drosophila</i> CNS neurons essential for viability, whereas more distal regulatory elements are important for expression in PNS sensory neurons. In this study we identify the POU domain transcription factor abnormal chemosensory jump 6 (Acj6) as a necessary positive transcriptional regulator for cholinergic locus expression in primary olfactory neurons. Choline acetyltransferase enzyme activity, protein levels, mRNA, and a fluorescent cholinergic reporter gene are all decreased in olfactory neurons of<i>acj6</i> mutants. Decreased cholinergic expression was observed in both adults and larvae. The presence of a specific Acj6 binding site has been identified in the cholinergic locus 5′ flanking DNA, suggesting that Acj6 may play a direct role in specifying the cholinergic neurotransmitter phenotype of most olfactory neurons. Transgenic expression of two different isoforms of Acj6 restricted to olfactory neurons indicates that additional <i>trans</i>factors may be required for cholinergic locus expression. Transgenic expression in all cholinergic neurons, however, results in lethality when a POU IV box element is absent but is essentially benign when present, indicating the importance of this motif in specifying different functional roles for Acj6.