A Specific Neuroligin3-aNeurexin1Signaling Regulates GABAergic Synaptic Function in Mouse Hippocampus

Synapses are fundamental organizers of precise signal propagation between neurons. Maintaining synapse assemblies require interactions between pre- and post- synaptic proteins, notably cell adhesion molecules (CAMs). It has been proposed that the function of Neuroligins (Nlgn1 - 4), postsynaptic CAMs, relies on the formation of trans-synaptic complexes with Neurexins (Nrxs), presynaptic CAMs. Nlgn3 is a unique Nlgn isoform that localizes at both excitatory and inhibitory synapses. However, Nlgn3 function mediated through Nrx interaction is mostly unknown. Here, we find for the first time that Nlgn3 localizes at postsynaptic sites apposing vesicular glutamate transporter 3 (VGT3)-expressing inhibitory terminals. Overexpression and knockdown approaches indicate that Nlgn3 regulates VGT3-positive inhibitory interneuron-mediated synaptic transmission. Fluorescent in situ hybridization and single-cell RNA sequencing studies revealed that aNrxn1 and ßNrxn3 are VGT3 interneuron-specific Nrxn isoforms and the expression levels of Nrxn splice isoforms are highly diverse in VGT3 interneurons, respectively. Most importantly, postsynaptic Nlgn3 requires presynaptic aNrx1+AS4 expressed in VGT3-positive interneurons to regulate inhibitory synaptic transmission. Our results strongly suggest that specific Nlgn-Nrx interaction generate distinct functional properties at synapses. Overall design: The cytosol of single cell VGT3-, Pv- and Sst-positive inhibitory interneuron was harvested using the whole cell patch-clamp technique