Flybow: genetic multicolor cell labeling for neural circuit analysis in Drosophila melanogaster

A genetic multicolor cell-labeling technique for Droshophila melanogaster , Flybow, is described and applied to the study of neural circuits. This method implements a variant of the mouse Brainbow strategy in combination with specific neuronal targeting using the Gal-4–upstream activating sequence system to select for membrane-tethered fluorescent proteins. Also in this issue, Hampel et al . report a similar strategy, Drosophila Brainbow, to select for epitope-tagged proteins detectable via immunofluorescence. To facilitate studies of neural network architecture and formation, we generated three Drosophila melanogaster variants of the mouse Brainbow-2 system, called Flybow. Sequences encoding different membrane-tethered fluorescent proteins were arranged in pairs within cassettes flanked by recombination sites. Flybow combines the Gal4-upstream activating sequence binary system to regulate transgene expression and an inducible modified Flp- FRT system to drive inversions and excisions of cassettes. This provides spatial and temporal control over the stochastic expression of one of two or four reporters within one sample. Using the visual system, the embryonic nervous system and the wing imaginal disc, we show that Flybow in conjunction with specific Gal4 drivers can be used to visualize cell morphology with high resolution. Finally, we demonstrate that this labeling approach is compatible with available Flp- FRT -based techniques, such as mosaic analysis with a repressible cell marker; this could further support the genetic analysis of neural circuit assembly and function.