Cell type-specific transcriptional regulation of the drosophila FMRFamide neuropeptide gene

We have used IacZ reporter gene constructs to study the promoter/enhancer regions of the Drosophila FMRFamide neuropeptide gene in germ line transformants. FMRFamide is normally expressed ∼60 diverse neurons of the larval CNS that represent ∼15 distinct cell types. An 8 kb FMRFamide DNA fragment (including 5 kb of 5′ upstream sequence) was sufficient to direct a pattern of IacZ expression that mimicked nearly all spatial aspects of the normal pattern. This result indicates that the cell-specific regulation of FMRFamide expression is largely generated by transcriptional mechanisms. Reporter gene expression was lost from selected cell types when smaller fragments were tested, suggesting that multiple control regions are included in the FMRFamide promoter. One region (a 300 by fragment from -476 to -162) acted as an enhancer for 1 of the ∼15 FMRFamide-positive cell types, the OL2 neurons. These results suggest that, in the mature nervous system, the complex pattern of FMRFamide neuropeptide gene expression derives from the activity of discrete, cell type-specific enhancers that are independently regulated.