The brain’s immense computational capabilities and complex nature are fundamentally based on the extensive molecular diversity found within its synapses. Synaptic molecular diversity arises from multiple layers, which comprise precise transcript processing, dynamic posttranslational modifications, and defined orchestration of the macromolecular assembly at the pre-and post synaptic membranes, tailoring the specialized functional attributes of individual synapses. At the presynaptic site, the efficiency and timing of synaptic vesicle (SV) release is modulated by the nanoscale organization of the Active Zone (AZ), which coordinates the physical coupling between voltage-gated Ca2+ Channels (VGCCs) and SV release sites. In Drosophila melanogaster, the AZ structure relies on the major scaffold protein Bruchpilot (BRP), whose N-terminal end mediates VGCCs clustering, while its C-terminal end is required for SV tethering. BRP is also crucially involved in the dynamic presynaptic remodeling of the AZ in the adult brain, essential for supporting memory formation. Despite the characterization and progressive understanding of the individual cytomatrix molecular components, comprehension of the principles governing AZ diversification across the Drosophila CNS remains scarce. Consequently, the ultimate connection between functional diversity of synapses and their molecular arrangements remains largely elusive. I here provide a systematic analysis of abundance and nanoscopic positioning of core AZ proteins - including Blobby, RIM-BP and BRP- within the different lobes of the mushroom body (MB), a central brain structure vital for higher-order functions such as learning and memory in adult Drosophila. Furthermore, this thesis bridges the differential distribution of AZ components between the lobes with their contribution to the formation of different forms of olfactory memory. The combination of proteomic, biochemical, and immunohistochemical approaches presented in the results section, moreover, provides a framework for discussing a broader spectrum of BRP isoforms. The potential significance of multiple BRP isoforms in modulating functional performance at specific synapse populations within the Drosophila CNS introduces novel hues of complexity into the AZ diversity picture. The eight new BRP monoclonal antibodies - whose characterization is integral part of this thesis - offer a wide array of possibilities to further explore the architecture, localization and plasticity roles of BRP and its isoforms at the AZ. In the concluding section of this thesis, I employed immuno-histochemistry, proteomics, and behavioral assays, to characterize the phenotype of BRP5.20 as a mushroom body-specific BRP isoform. I also provide evidence of presynaptic AZs, positive for BRP5.20, in KC dendrites within the calyx of adult Drosophila, confirming that they are not solely postsynaptic. The characterization of KC-specific BRP isoforms and their role in AZ plasticity appears promising, considering that a memory trace for olfactory conditioning is established at the AZs of KCs. Collectively, the results described in this thesis provide insights into the compartmentwise molecular heterogeneity of the AZ composition within the Drosophila mushroom body, and propose a frame of discussion bridging the nanoscopic diversity of the AZ with the configuration of specific memory circuits.
