High-throughput synapse profiling reveals cell-type-specific spatial configurations in the fly brain

Characterization of intracellular synapse heterogeneity aides to understand the intricate computational logic of neuronal circuits. Despite recent advances in connectomics, the spatial patterns of synapses and their inter-individual variability remain largely unknown. Using directed split-GFP reconstitution, we achieved visualization of endogenous Bruchpilot (Brp) proteins, the presynaptic active zone (AZ) scaffold, in a cell-type-specific manner. By developing a high-throughput quantification pipeline, we profiled AZ structures in identified neurons of the mushroom body circuit, where intracellular synaptic pattern is crucial due to its compartmentalized connectivity. Quantitative characterization of the pattern of Brp clusters across multiple individuals revealed cell-type-dependent synapse heterogeneity and stereotypy. Furthermore, we discovered previously unidentified sub-compartmental synapse configuration and its regulation by cAMP signaling. These results of synapse profiling uncovered multi-layered organizations of AZs, ranging from neighboring synapses to consistent patterns across individuals.