Hexameric GFP and mCherry reporters for the Drosophila GAL4, Q, and LexA transcription systems.

The ability to distinguish cells and tissues of interest is critical for understanding their biological importance. In genetic model organisms, a prominent approach for discerning particular cells or tissues from others is the use of cell or tissue-specific enhancers to drive fluorescent reporters. This approach, however, is often limited by the brightness of the fluorescent reporter. To augment the ability to visualize cells or tissues of interest in Drosophila melanogaster, homo-hexameric GFP and mCherry reporters were developed for the GAL4, Q, and LexA transcription systems and functionally validated in vivo. The GFP and mCherry homo-hexameric fusion proteins exhibited significantly enhanced fluorescence as compared to monomeric fluorescent reporters and could be visualized by direct fluorescence throughout the cytoplasm of neurons, including the fine processes of axons and dendrites. These high-sensitivity fluorescent reporters of cell morphology can be utilized for a variety of purposes, especially facilitating fluorescence-based genetic screens for cell morphology phenotypes. These results suggest that the strategy of fusing monomeric fluorescent proteins in tandem to enhance brightness should be generalizable to other fluorescent proteins and other genetic model organisms.