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

Abstract

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.

Modality-specific circuits for skylight orientation in the fly visual system

“…F. Quantitative comparison of vertical extension of Dm-DRA2 cells, activity GRASP signal from (D) and distribution of R8 presynaptic sites (from Figure 1). G. Expression of DRA.R8-Gal4 from brain used for trans-Tango tracing 13 . H. Sparse trans-Tango tracing (3 days, 25ºC degrees) reveals cells resembling Dm-DRA2 (note presence of vertical projections and absence of deep projections).…”

“…In recent years, the quickly growing arsenal of molecular-genetic tools available in Drosophila has been used to dissect the neuronal circuits underlying specific visual behaviors via the cell type-specific visualization and/or manipulation of neuronal activity. Additionally, new tools for the detailed characterization of neuronal morphology [9][10][11] and synaptic connectivity 12,13 have been developed. As a result, the computation of visual motion within the optic lobes downstream of the fly's stereotypical unit eyes (ommatidia) has been dissected with great success, at a cellular and synaptic level 8,14 .…”

“…In this study, we provide the first detailed neuroanatomical characterization of neuronal elements that are post-synaptic to R7 and R8 photoreceptor cells in the DRA region of the medulla of Drosophila. Using genetic redesign of the retinal mosaic, activity-dependent 'GFP Reconstitution Across Synaptic Partners (GRASP) 12 and the trans-synaptic tracer 'trans-Tango' 13 we show that DRA.R7 and DRA.R8 cells are synaptically connected to distinct, newly-discovered Dm-DRA subtypes (Dm-DRA1 versus Dm-DRA2, respectively). These cells stratify in similar sublayers of M6 and specifically contact polarization-sensitive inputs, while avoiding contacts with color-sensitive non-DRA inputs.…”

Split-TurboID enables contact-dependent proximity labeling in cells

“…To test this, we designed a signaling network that utilizes the trans-cellular interaction between glucagon peptide and its receptor (GCGR), employed in the trans-synaptic tracing tool trans-Tango (37). In our design, "receiver" cells express glucagon receptor (GCGR) and arrestin, each fused to a split-TurboID fragment.…”

Building a functional connectome of the Drosophila central complex

“…But even when used in combination with synaptic markers (Nicolai et al, 2010;DiAntonio et al, 1993;Zhang et al, 2002;Fouquet et al, 2009), such methods do not offer definitive evidence of synaptic connections, as they rely solely on the proximity of putative pre-and post-synaptic compartments. Recently, promising trans-synaptic genetic tagging systems (Talay et al, 2017;hao Huang et al, 2017) have been developed to address some of these issues. However, none of these approaches provide any insight into the functional properties of potential connections.…”