The calcium channel subunit α2δ-3 organizes synapses via a novel activity-dependent, autocrine BMP signaling pathway
Synapses are highly specialized for neurotransmitter signaling, yet activity-dependent growth factor release also plays critical roles at synapses. While efficient neurotransmitter signaling is known to rely on precise apposition of release sites and neurotransmitter receptors, molecular mechanisms enabling high-fidelity growth factor signaling within the synaptic microenvironment remain obscure. Here we show that the auxiliary calcium channel subunit 2{delta}-3 promotes the function of a novel activity-dependent autocrine BMP signaling pathway at the Drosophila NMJ. 2{delta} proteins have conserved synaptogenic activity, although how they execute this function has remained elusive. We find that 2{delta}-3 provides an extracellular scaffold for autocrine BMP signaling, suggesting a new mechanistic framework for understanding 2{delta}s conserved role in synapse organization. We further establish a transcriptional requirement for activity-dependent, autocrine BMP signaling in determining synapse density, structure, and function. We propose that activity-dependent, autocrine signals provide neurons with continuous feedback on their activity state and are thus well poised to modulate synapse structure and function.