A trans-synaptic IgLON adhesion molecular complex directly contacts and clusters a nicotinic receptor

The clustering of neurotransmitter receptors at appropriate postsynaptic sites is essential for controlling synaptic transmission. While most known mechanisms involve receptor binding with cytoplasmic scaffolds, recent evidence highlights the importance of extracellular interactions that directly target receptors. Using Caenorhabditis elegans, we identified a trans-synaptic complex that involves RIG-5 and ZIG-8, two adhesion molecules of the immunoglobulin (Ig) superfamily and orthologous to Drosophila DIPs and Dprs, and mammalian IgLONs. Our results show that RIG-5 and ZIG-8 are anchored in the pre- and postsynaptic membranes, respectively, and interact in vivo via their first Ig domains. Furthermore, ZIG-8 directly binds a α7-like acetylcholine receptor (AChR), known as ACR-16, via a cis-interaction between its Ig2 domain and the base of the extracellular AChR domain. This study provides direct evidence that trans-synaptic IgLON interactions can organize neurochemical synapses and suggests that the IgLONs may directly interact with ionotropic receptors in the mammalian nervous system.