Presynaptic αδs specify synaptic gain, not synaptogenesis, in the mammalian brain.

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