Fig. 2. Key molecular interactions of LAR and liprin at the synapse. The extracellular domains of LAR have three identified ligands, which regulate the function and/or localization of LAR at the synapse. Nidogen genetically interacts with PTP-3 in C. elegans and may regulate active zone morphogenesis through its ability to localize PTP-3 to the synapse. Dallylike and syndecan both bind to the extracellular domains of LAR in Drosophila and have distinct effects on synapse formation; syndecan positively regulates LAR to promote synapse growth, whereas Dallylike inhibits its ability to limit active zone size. Inside the presynaptic terminus, liprin binds the MALS/Veli-Cask-Mint1 complex, ERC2, and RIM. Through these interactions, liprin is able to promote the formation of an electron-dense, tightly clustered, robust active zone.