Alternative splicing of synaptotagmin 7 regulates oligomerization and short-term synaptic plasticity.

Synaptic plasticity is crucial for learning and memory. The presynaptic calcium sensor synaptotagmin 7 (syt7) regulates aspects of short-term plasticity (STP), but the underlying mechanisms remain unclear. Here, we show that alternative splicing of the syt7 juxtamembrane linker acts as a molecular switch at both biochemical and functional levels. The α and β variants undergo liquid-liquid phase separation to form condensates, while the γ variant forms aggregates. Using iGluSnFR imaging, we found that, when expressed at equal levels, these three isoforms also diverge regarding their abilities to regulate two key aspects of STP: paired-pulse facilitation and synaptic depression. Stimulated emission depletion microscopy showed that all three isoforms form active zone-associated clusters that colocalize with syt1, while minimal photon flux superresolution microscopy resolved syt7 clusters within the active zone, well-positioned to directly control synaptic vesicle dynamics. Thus, alternative splicing might fine-tune STP by differentially impacting syt7 oligomerization.