Transsynaptic Mapping of Second-Order Taste Neurons in Flies by trans-Tango

Summary Mapping neural circuits across defined synapses is essential for understanding brain function. Here we describe trans -Tango, a technique for anterograde transsynaptic circuit tracing and manipulation. At the core of trans -Tango is a synthetic signaling pathway that is introduced into all neurons in the animal. This pathway converts receptor activation at the cell surface into reporter expression through site-specific proteolysis. Specific labeling is achieved by presenting a tethered ligand at the synapses of genetically defined neurons, thereby activating the pathway in their postsynaptic partners and providing genetic access to these neurons. We first validated trans -Tango in the Drosophila olfactory system and then implemented it in the gustatory system, where projections beyond the first-order receptor neurons are not fully characterized. We identified putative second-order neurons within the sweet circuit that include projection neurons targeting known neuromodulation centers in the brain. These experiments establish trans -Tango as a flexible platform for transsynaptic circuit analysis.