Presynaptic α₂δs specify synaptic gain, not synaptogenesis, in the mammalian brain

The α₂δs are a family of extracellular synaptic molecules that are auxiliary subunits of voltage-gated Ca²⁺ channel (Ca_V) complexes. They are linked to brain disorders and are drug targets. The α₂δs are implicated in controlling synapse development and function through distinct Ca_V-dependent and Ca_V-independent pathways. However, the mechanisms of action remain enigmatic since synapses contain mixtures of α₂δ isoforms in the pre- and postsynaptic compartments. We developed a triple conditional knockout mouse model and demonstrated the combined selective presynaptic ablation of α₂δs in vivo in a developing mammalian glutamatergic synapse. We identified presynaptic α₂δs as positive regulators of Munc13-1 levels, an essential neurotransmitter release protein. We found that mammalian synapse development, presynaptic Ca_V2.1 organization, and the transsynaptic alignment of presynaptic release sites and postsynaptic glutamate receptors are independent of presynaptic α₂δs. Therefore, our results define presynaptic α₂δ regulatory roles and suggest a new α₂δ role in controlling synaptic strength and plasticity.