Functional Labeling of Individualized Post-Synaptic Neurons using Optogenetics and trans-Tango

Neural circuitry, or how neurons connect across brain regions to form functional units, is the fundamental basis of all brain processing and behavior. There are several neural circuit analysis tools available across different model organisms, but currently the field lacks a comprehensive method that can 1) target post-synaptic neurons using a pre-synaptic driver line, 2) assess post-synaptic neuron morphology, and 3) test behavioral response of the post-synaptic neurons in an isolated manner. This work will present FLIPSOT, or Functional Labeling of Individualized Post-Synaptic Neurons using Optogenetics and trans-Tango, which is a method developed to fulfill all three of these conditions. FLIPSOT uses a pre-synaptic driver line to drive trans-Tango, triggering heat-shock-dependent expression of post-synaptic optogenetic receptors. When heat shocked for a suitable duration of time, optogenetic activation or inhibition is made possible in a randomized selection of post-synaptic cells, allowing testing and comparison of function. Finally, imaging of each brain confirms which neurons were targeted per animal, and analysis across trials can reveal which post-synaptic neurons are necessary and/or sufficient for the relevant behavior.

FLIPSOT is then tested within Drosophila melanogaster to evaluate the necessity and sufficiency of post-synaptic neurons in the Drosophila Heating Cell circuit, which is a circuit that functions to drive warmth avoidance behavior. FLIPSOT presents a new combinatory tool for evaluation of behavioral necessity and sufficiency of post-synaptic cells. The tool can easily be utilized to test many different behaviors and circuits through modification of the pre-synaptic driver line. Lastly, the success of this tool within flies paves the way for possible future adaptation in other model organisms, including mammals.