Synapse and Active Zone Assembly in the Absence of Presynaptic Ca2+ Channels and Ca2+ Entry.

Presynaptic Ca V 2 channels are essential for Ca2+-triggered exocytosis. In addition, there are two competing models for their roles in synapse structure. First, Ca2+ channels or Ca2+ entry may control synapse assembly. Second, active zone proteins may scaffold Ca V 2s to presynaptic release sites, and synapse structure is Ca V 2 independent. Here, we ablated all three Ca V 2s using conditional knockout in cultured hippocampal neurons or at the calyx of Held, which abolished evoked exocytosis. Compellingly, synapse and active zone structure, vesicle docking, and transsynaptic nano-organization were unimpaired. Similarly, long-term blockade of action potentials and Ca2+ entry did not disrupt active zone assembly. Although Ca V 2 knockout impaired the localization of β subunits, α2δ-1 localized normally. Rescue with Ca V 2 restored exocytosis, and Ca V 2 active zone targeting depended on the intracellular C-terminus. We conclude that synapse assembly is independent of Ca V 2s or Ca2+ entry through them. Instead, active zone proteins recruit and anchor Ca V 2s via Ca V 2 C-termini. • Ca V 2s mediate evoked synaptic vesicle release and cannot be replaced by Ca V 1 or Ca V 3 • Active zone nano-assemblies and docking persist after removing Ca V 2s or Ca2+ entry • α2δ-1 localization within nerve terminals is broad and does not require Ca V 2s • Ca V 2 C-termini and their binding to active zone proteins mediate Ca V 2 targeting Ca V 2 channels provide Ca2+ for triggering neurotransmitter release at central synapses. Held et al. remove all Ca V 2s and Ca2+ entry and find that synaptic protein nano-assemblies persist and synapse ultrastructure is unimpaired despite abolishing synaptic transmission. Rescue experiments establish that Ca V 2 C-termini are important for channel anchoring at active zones. [ABSTRACT FROM AUTHOR]