Membrane-associated mucin domain-containing glycosylphosphatidylinositol anchor proteins (MDGAs) bind directly to neuroligin-1 (NL1) and neuroligin-2 (NL2), thereby respectively regulating excitatory and inhibitory synapse development. However, the mechanisms by which MDGAs modulate NL activity to specify development of the two synapse types remain unclear. Here, we determined the crystal structures of human NL2/MDGA1 Ig1-3 complex, revealing their stable 2:2 arrangement with three interaction interfaces. Cell-based assays using structure-guided, site-directed MDGA1 mutants showed that all three contact patches were required for the MDGA's negative regulation of NL2-mediated synaptogenic activity. Furthermore, MDGA1 competed with neurexins for NL2 via its Ig1 domain. The binding affinities of both MDGA1 and MDGA2 for NL1 and NL2 were similar, consistent with the structural prediction of similar binding interfaces. However, MDGA1 selectively associated with NL2, but not NL1, in vivo. These findings collectively provide structural insights into the mechanism by which MDGAs negatively modulate synapse development governed by NLs/neurexins.

The four members of the LRRTM family (LRRTM1-4) are postsynaptic adhesion molecules essential for excitatory synapse development. They have also been implicated in neuropsychiatric diseases. Here, we focus on LRRTM3, showing that two distinct LRRTM3 variants generated by alternative splicing regulate LRRTM3 interaction with PSD-95, but not its excitatory synapse-promoting activity. Overexpression of either LRRTM3 variant increased excitatory synapse density in dentate gyrus (DG) granule neurons, whereas LRRTM3 knockdown decreased it. LRRTM3 also controlled activity-regulated AMPA receptor surface expression in an alternative splicing-dependent manner. Furthermore, Lrrtm3-knockout mice displayed specific alterations in excitatory synapse density, excitatory synaptic transmission and excitability in DG granule neurons but not in CA1 pyramidal neurons. Lastly, LRRTM3 required only specific splice variants of presynaptic neurexins for their synaptogenic activity. Collectively, our data highlight alternative splicing and differential presynaptic ligand utilization in the regulation of LRRTMs, revealing key regulatory mechanisms for excitatory synapse development.

ZnO nanorod arrays fabricated on ZnO buffer layers on Si wafers were grown using a low-temperature solution method and were characterized by various techniques. Buffer layers were prepared using metal organic chemical vapor deposition and a sputter-oxidation method. Aligned ZnO nanorods were deposited at 90°C on the substrates by a hydrothermal treatment using a zinc salt and aqueous ammonia solution. The ZnO nanorod arrays were characterized by scanning electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, Raman spectroscopy, and photoluminescence spectroscopy. The as-grown ZnO nanorod arrays exhibited broad deep-level emission centered at ∼564nm. The intensity of the deep-level emission decreased and band edge emission centered at 379nm appeared after air annealing. Samples annealed in hydrogen showed only band edge emission.

Calsyntenin-3 (Clstn3) is a postsynaptic adhesion molecule that induces presynaptic differentiation via presynaptic neurexins (Nrxns), but whether Nrxns directly bind to Clstn3 has been a matter of debate. Here, using LC–MS/MS–based protein analysis, confocal microscopy, RNAscope assays, and electrophysiological recordings, we show that β-Nrxns directly interact via their LNS domain with Clstn3 and Clstn3 cadherin domains. Expression of splice site 4 (SS4) insert–positive β-Nrxn variants, but not insert–negative variants, reversed the impaired Clstn3 synaptogenic activity observed in Nrxn-deficient neurons. Consistently, Clstn3 selectively formed complexes with SS4–positive Nrxns in vivo. Neuron-specific Clstn3 deletion caused significant reductions in number of excitatory synaptic inputs. Moreover, expression of Clstn3 cadherin domains in CA1 neurons of Clstn3 conditional knockout mice rescued structural deficits in excitatory synapses, especially within the stratum radiatum layer. Collectively, our results suggest that Clstn3 links to SS4–positive Nrxns to induce presynaptic differentiation and orchestrate excitatory synapse development in specific hippocampal neural circuits, including Schaffer collateral afferents.

Gephyrin is a central scaffold protein that mediates development, function, and plasticity of mammalian inhibitory synapses by interacting with various inhibitory synaptic proteins. Here, we show that IQSEC3, a guanine nucleotide exchange factor for ARF6, directly interacts with gephyrin, an interaction that is critical for the inhibitory synapse localization of IQSEC3. Overexpression of IQSEC3 increases inhibitory, but not excitatory, synapse density in a guanine nucleotide exchange factor activity-dependent manner. Conversely, knockdown of IQSEC3 decreases size of gephyrin cluster without altering gephyrin puncta density. Collectively, these data reveal that IQSEC3 acts together with gephyrin to regulate inhibitory synapse development.