Active Zone Scaffold Protein Ratios Tune Functional Diversity across Brain Synapses

Abstract

High-throughput electron microscopy has started to reveal synaptic connectivity maps of single circuits and whole brain regions, for example, in the Drosophila olfactory system. However, efficacy, timing, and frequency tuning of synaptic vesicle release are also highly diversified across brain synapses. These features critically depend on the nanometer-scale coupling distance between voltage-gated Ca channels (VGCCs) and the synaptic vesicle release machinery. Combining light super resolution microscopy with in vivo electrophysiology, we show here that two orthogonal scaffold proteins (ELKS family Bruchpilot, BRP, and Syd-1) cluster-specific (M)Unc13 release factor isoforms either close (BRP/Unc13A) or further away (Syd-1/Unc13B) from VGCCs across synapses of the Drosophila olfactory system, resulting in different synapse-characteristic forms of short-term plasticity. Moreover, BRP/Unc13A versus Syd-1/Unc13B ratios were different between synapse types. Thus, variation in tightly versus loosely coupled scaffold protein/(M)Unc13 modules can tune synapse-type-specific release features, and "nanoscopic molecular fingerprints" might identify synapses with specific temporal features.

Depopulation of α-synuclein aggregates is associated with rescue of dopamine neuron dysfunction and death in a new Parkinson’s disease model

“…To further characterize the progression of striatal synaptic 1-120hαSyn aggregation, we used dSTORM, which allows detection of protein distribution at single molecule level and 20nm resolution. Although dSTORM has been successfully employed to study synaptic proteins (Bar-On et al, 2011;Bar-On et al, 2012;Bielopolski et al, 2014;Fulterer et al, 2018;Tang et al, 2016) we believe that this is the first time that dSTORM is used to analyze the progression and rescue of presynaptic αSyn pathology in vivo in brains of a PD mouse model. dSTORM confirmed a progressive aggregation of 1-120hαSyn in the MI2 mouse striatum.…”

Regulation of synaptic release‐site Ca2+ channel coupling as a mechanism to control release probability and short‐term plasticity

“…Alterations in the stoichiometry of those AZ scaffolding proteins could therefore be a general principle to determine the ratio of closely vs. loosely coupled release sites, thereby determining synaptic pV r and STP. In fact, it was recently shown that the ratio between BRP and Syd‐1 varied largely between synapse types of the Drosophila brain, in line with cell‐specific regulation of coupling distances . High BRP/Unc13A levels supported fast synaptic transmission and STD, while Syd‐1/Unc13B rich synapses were rather slow and exhibited STF .…”

“…In fact, it was recently shown that the ratio between BRP and Syd‐1 varied largely between synapse types of the Drosophila brain, in line with cell‐specific regulation of coupling distances . High BRP/Unc13A levels supported fast synaptic transmission and STD, while Syd‐1/Unc13B rich synapses were rather slow and exhibited STF . Syd‐1 and Liprin‐α have homologs in mammals and C. elegans .…”

“…In some cases, these differences may be explained by the utilization of a specialized molecular SV fusion machinery (i.e. different Ca 2+ sensors of the synaptotagmin family or of (M)Unc13 isoforms ). Yet, most synapses appear to utilize the same set of evolutionarily highly conserved release factors mentioned above, suggesting additional layers of control.…”

“…(A) SV ‐release probability decreases from 1 (red) to 0 (dark blue) with increasing distances between the SV ‐release site and the Ca 2+ source. For distances between 65 and 85 nm from the AZ center, where Drosophila Unc13A is located in the central and peripheral nervous system (shaded in gray), pV r is around 0.2. Likewise, paired‐pulse ratios (second peak amplitude divided by first, 10 ms interstimulus interval) steeply increase in a distance‐dependent manner.…”