A genetic strategy for targeting local astrocytes in adult Drosophila

Astrocytes are the brain's major glial population and have been associated with a vast number of functions. To probe this diversity and to reach a similar level of understanding about astrocyte physiology that we have about neurons, we need genetic tools targeting specific astrocyte subpopulations. In Drosophila, available tools have historically been restricted to driver lines driving expression in astrocytes throughout the brain. To target specific astrocytes, we have optimized the genetic tool transneuronal control of transcription (TRACT; referred to as astro-TRACT), allowing effector expression specifically in local astrocytes of a given neuronal circuit. We analyzed the tool's specificity, sensitivity, and reproducibility across various mushroom body (MB) split-Gal4 drivers. We found that the number of pre-synapses correlates positively with labeling efficiency and that single local astrocytes around MB medial compartments project into the ellipsoid body (EB). Astro-TRACT will be valuable to investigate mechanistic astrocyte-neuron signaling, functional, and structural astrocytic diversity across the adult fly brain.