Activity-Dependent Alternative Splicing of Adhesion-GPCR Latrophilin-3 Controls Synapse Formation

Abstract

How synapses are assembled and specified in brain is incompletely understood. Latrophilin- 3, a postsynaptic adhesion-GPCR, mediates Schaffer-collateral synapse formation in the hippocampus but the mechanisms involved remained unclear. Here we show that Latrophilin-3 organizes synapses by a convergent dual-pathway mechanism by which Latrophilin-3 simultaneously activates GS/cAMP-signaling and recruits phase-separated postsynaptic protein scaffolds. We found that cell type-specific alternative splicing of Latrophilin-3 controls its G protein coupling mode, resulting in Latrophilin-3 variants that predominantly signal via Gs and cAMP or via G12/13. A CRISPR-mediated genetic switch of Latrophilin-3 alternative splicing from a GS- to a G12/13-coupled mode impaired synaptic connectivity similar to the overall deletion of Latrophilin-3, suggesting that GS/cAMP- signaling by Latrophilin-3 splice variants mediates synapse formation. Moreover, GS- but not G12/13-coupled splice variants of Latrophilin-3 recruit phase-transitioned postsynaptic protein scaffolds that are clustered by binding of presynaptic Latrophilin-3 ligands. Strikingly, neuronal activity promotes alternative splicing of the synaptogenic variant of Latrophilin-3, thereby enhancing synaptic connectivity. Together, these data suggest that activity- dependent alternative splicing of a key synaptic adhesion molecule controls synapse formation by parallel activation of two convergent pathways, GS/cAMP signaling and the phase separation of postsynaptic protein scaffolds.