A neuron-specific enhancer of the Drosophila dopa decarboxylase gene

At least two cis-regulatory elements are necessary for correct neuron-specific expression of the Drosophila melanogaster dopa decarboxylase gene, Ddc. In addition to a previously described proximal element located approximately 60 bp upstream of the mRNA start site, we have now characterized a distal approximately 600-bp DNA fragment, extending from -1019 to -1623 bp, which possesses enhancer-like properties and is essential for normal neuron-specific expression. Immunofluorescent labeling of neurons expressing deleted Ddc genes indicates that this region contains both general neuronal regulatory elements and cell-specific elements that selectively affect Ddc expression in either dopaminergic or serotonergic neurons. These selective effects can be correlated with the removal of sequence elements that are protected from DNase digestion by factors present in embryonic nuclear extracts. Several of these elements are also homologous to sequences located upstream of the evolutionarily diverged Ddc gene of Drosophila virilis. These results suggest that the neuron-specific expression of Ddc results from the combined action of several factors binding within this distal enhancer region.