Identification and functional characterization of rare mutations of the neuroligin-2 gene (NLGN2) associated with schizophrenia

Neuroligin 4 regulates synaptic growth via the bone morphogenetic protein (BMP) signaling pathway at the Drosophila neuromuscular junction

The neuroligin (Nlg) family of neural cell adhesion molecules is thought to be required for synapse formation and development and has been linked to the development of autism spectrum disorders in humans. In Drosophila melanogaster, mutations in the neuroligin 1–3 genes have been reported to induce synapse developmental defects at neuromuscular junctions (NMJs), but the role of neuroligin 4 (dnlg4) in synapse development has not been determined. Here, we report that the Drosophila neuroligin 4 (DNlg4) is different from DNlg1–3 in that it presynaptically regulates NMJ synapse development. Loss of dnlg4 results in reduced growth of NMJs with fewer synaptic boutons. The morphological defects caused by dnlg4 mutant are associated with a corresponding decrease in synaptic transmission efficacy. All of these defects could only be rescued when DNlg4 was expressed in the presynapse of NMJs. To understand the basis of DNlg4 function, we looked for genetic interactions and found connections with the components of the bone morphogenetic protein (BMP) signaling pathway. Immunostaining and Western blot analyses demonstrated that the regulation of NMJ growth by DNlg4 was due to the positive modulation of BMP signaling by DNlg4. Specifically, BMP type I receptor thickvein (Tkv) abundance was reduced in dnlg4 mutants, and immunoprecipitation assays showed that DNlg4 and Tkv physically interacted in vivo. Our study demonstrates that DNlg4 presynaptically regulates neuromuscular synaptic growth via the BMP signaling pathway by modulating Tkv.

Cysteine-rich whey protein isolate (Immunocal®) ameliorates deficits in the GFAP.HMOX1 mouse model of schizophrenia

Schizophrenia is a neuropsychiatric disorder that features neural oxidative stress and glutathione (GSH) deficits. Oxidative stress is augmented in brain tissue of GFAP.HMOX1 transgenic mice which exhibit schizophrenia-relevant characteristics. The whey protein isolate, Immunocal® serves as a GSH precursor upon oral administration. In this study, we treated GFAP.HMOX1 transgenic mice daily with either Immunocal (33mg/ml drinking water) or equivalent concentrations of casein (control) between the ages of 5 and 6.5 months. Immunocal attenuated many of the behavioral, neurochemical and redox abnormalities observed in GFAP.HMOX1 mice. In addition to restoring GSH homeostasis in the CNS of the transgenic mice, the whey protein isolate augmented GSH reserves in the brains of wild-type animals. These results demonstrate that consumption of whey protein isolate augments GSH stores and antioxidant defenses in the healthy and diseased mammalian brain. Whey protein isolate supplementation (Immunocal) may constitute a safe and effective modality for the management of schizophrenia, an unmet clinical imperative.

Molecular Mechanism of MDGA1: Regulation of Neuroligin 2:Neurexin Trans-synaptic Bridges

Neuroligins and neurexins promote synapse development and validation by forming trans-synaptic bridges spanning the synaptic cleft. Select pairs promote excitatory and inhibitory synapses, with neuroligin 2 (NLGN2) limited to inhibitory synapses and neuroligin 1 (NLGN1) dominating at excitatory synapses. The cell-surface molecules, MAM domain-containing glycosylphosphatidylinositol anchor 1 (MDGA1) and 2 (MDGA2), regulate trans-synaptic adhesion between neurexins and neuroligins, impacting NLGN2 and NLGN1, respectively. We have determined the molecular mechanism of MDGA action. MDGA1 Ig1-Ig2 is sufficient to bind NLGN2 with nanomolar affinity; its crystal structure reveals an unusual locked rod-shaped array. In the crystal structure of the complex, two MDGA1 Ig1-Ig2 molecules each span the entire NLGN2 dimer. Site-directed mutagenesis confirms the observed interaction interface. Strikingly, Ig1 from MDGA1 binds to the same region on NLGN2 as neurexins do. Thus, MDGAs regulate the formation of neuroligin-neurexin trans-synaptic bridges by sterically blocking access of neurexins to neuroligins.

Regulation of Alpha-Secretase ADAM10 In vitro and In vivo: Genetic, Epigenetic, and Protein-Based Mechanisms

ADAM10 (A Disintegrin and Metalloproteinase 10) has been identified as the major physiological alpha-secretase in neurons, responsible for cleaving APP in a non-amyloidogenic manner. This cleavage results in the production of a neuroprotective APP-derived fragment, APPs-alpha, and an attenuated production of neurotoxic A-beta peptides. An increase in ADAM10 activity shifts the balance of APP processing toward APPs-alpha and protects the brain from amyloid deposition and disease. Thus, increasing ADAM10 activity has been proposed an attractive target for the treatment of neurodegenerative diseases and it appears to be timely to investigate the physiological mechanisms regulating ADAM10 expression. Therefore, in this article, we will (1) review reports on the physiological regulation of ADAM10 at the transcriptional level, by epigenetic factors, miRNAs and/or protein interactions, (2) describe conditions, which change ADAM10 expression in vitro and in vivo, (3) report how neuronal ADAM10 expression may be regulated in humans, and (4) discuss how this knowledge on the physiological and pathophysiological regulation of ADAM10 may help to preserve or restore brain function.

Emerging Synaptic Molecules as Candidates in the Etiology of Neurological Disorders

Synapses are complex structures that allow communication between neurons in the central nervous system. Studies conducted in vertebrate and invertebrate models have contributed to the knowledge of the function of synaptic proteins. The functional synapse requires numerous protein complexes with specialized functions that are regulated in space and time to allow synaptic plasticity. However, their interplay during neuronal development, learning, and memory is poorly understood. Accumulating evidence links synapse proteins to neurodevelopmental, neuropsychiatric, and neurodegenerative diseases. In this review, we describe the way in which several proteins that participate in cell adhesion, scaffolding, exocytosis, and neurotransmitter reception from presynaptic and postsynaptic compartments, mainly from excitatory synapses, have been associated with several synaptopathies, and we relate their functions to the disease phenotype.

Neuroligin 2 R215H Mutant Mice Manifest Anxiety, Increased Prepulse Inhibition, and Impaired Spatial Learning and Memory

Neuroligin 2 (NLGN2) is a postsynaptic adhesion protein that plays an essential role in synaptogenesis and function of inhibitory neuron. We previously identified a missense mutation R215H of the NLGN2 in a patient with schizophrenia. This missense mutation was shown to be pathogenic in several cell-based assays. The objective of this study was to better understand the behavioral consequences of this mutation in vivo. We generated a line of transgenic mice carrying this mutation using a recombinant-based method. The mice were subjected to a battery of behavioral tests including open field locomotor activity assay, prepulse inhibition (PPI) assay, accelerated rotarod test, novel location and novel recognition tests, elevated plus-maze (EPM) test, and Morris water maze test. The transgenic animals were viable and fertile, but the Nlgn2 R215H knock-in (KI) homozygous mice showed growth retardation, anxiety-like behavior, increased PPI, and impaired spatial learning and memory. There was no significant interaction between sex and genotype in most behavioral tests; however, we observed a significant interaction between sex and genotype in EPM test in this study. Also, we found that the Nlgn2 R215H homozygous KI mice did not express the NLGN2 protein, resembling Nlgn2 knockout mice. Our results demonstrate that Nlgn2 R215H KI homozygous mice manifest several behavioral abnormalities similar to those found in psychiatric patients carrying NLGN2 mutations, indicating that dysfunction of NLGN2 contributes to the pathogenesis of certain psychiatric symptoms commonly present in various mental disorders, not limited to schizophrenia.

Cell adhesion molecules and sleep

Cell adhesion molecules (CAMs) play essential roles in the central nervous system, where some families are involved in synaptic development and function. These synaptic adhesion molecules (SAMs) are involved in the regulation of synaptic plasticity, and the formation of neuronal networks. Recent findings from studies examining the consequences of sleep loss suggest that these molecules are candidates to act in sleep regulation. This review highlights the experimental data that lead to the identification of SAMs as potential sleep regulators, and discusses results supporting that specific SAMs are involved in different aspects of sleep regulation. Further, some potential mechanisms by which SAMs may act to regulate sleep are outlined, and the proposition that these molecules may serve as molecular machinery in the two sleep regulatory processes, the circadian and homeostatic components, is presented. Together, the data argue that SAMs regulate the neuronal plasticity that underlies sleep and wakefulness.

Neurexin 1 (NRXN1) splice isoform expression during human neocortical development and aging

Neurexin 1 (NRXN1), a presynaptic cell adhesion molecule, is implicated in several neurodevelopmental disorders characterized by synaptic dysfunction including autism, intellectual disability and schizophrenia. To gain insight into NRXN1's involvement in human cortical development we used quantitative real-time PCR to examine the expression trajectories of NRXN1, and its predominant isoforms, NRXN1-α and NRXN1-β, in prefrontal cortex from fetal stages to aging. In addition, we investigated whether prefrontal cortical expression levels of NRXN1 transcripts are altered in schizophrenia or bipolar disorder in comparison with non-psychiatric control subjects. We observed that all three NRXN1 transcripts were highly expressed during human fetal cortical development, markedly increasing with gestational age. In the postnatal dorsolateral prefrontal cortex, expression levels were negatively correlated with age, peaking at birth until ~3 years of age, after which levels declined markedly to be stable across the lifespan. NRXN1-β expression was modestly but significantly elevated in the brains of patients with schizophrenia compared with non-psychiatric controls, whereas NRXN1-α expression was increased in bipolar disorder. These data provide novel evidence that NRXN1 expression is highest in human dorsolateral prefrontal cortex during critical developmental windows relevant to the onset and diagnosis of a range of neurodevelopmental disorders, and that NRXN1 expression may be differentially altered in neuropsychiatric disorders.

New insights into Alzheimer's disease pathogenesis: the involvement of neuroligins in synaptic malfunction

Synaptic damage is a key hallmark of Alzheimer's disease and the best correlate with cognitive decline ante mortem. Signature protein combinations arrayed at tightly apposed pre- and post-synaptic sites characterize different types of synapse. Neuroligins are postsynaptic cell adhesion molecules that interact with neurexins across the synaptic cleft. These pairings recruit receptors, channels and signal transduction molecules to the synapse, and help mediate trans-synaptic transmission. Dysfunction in the neuroligin family can disrupt neuronal networks and leads to neurodegeneration and other diseases. The extracellular domain of neuroligins is homologous with acetylcholinesterase but lacks residues required for enzymatic activity. This domain may interact pathogenically with β-amyloid. Here we summarize research over the last decade on the potential involvement of neuroligins in Alzheimer's disease.

Physical Interactions and Functional Relationships of Neuroligin 2 and Midbrain Serotonin Transporters

The neurotransmitter serotonin [5-hydroxytryptamine (5-HT)] modulates many key brain functions including those subserving sensation, emotion, reward, and cognition. Efficient clearance of 5-HT after release is achieved by the antidepressant-sensitive 5-HT transporter (SERT, SLC6A4). To identify novel SERT regulators, we pursued a proteomic analysis of mouse midbrain SERT complexes, evaluating findings in the context of prior studies that established a SERT-linked transcriptome. Remarkably, both efforts converged on a relationship of SERT with the synaptic adhesion protein neuroligin 2 (NLGN2), a post-synaptic partner for presynaptic neurexins, and a protein well-known to organize inhibitory GABAergic synapses. Western blots of midbrain reciprocal immunoprecipitations confirmed SERT/NLGN2 associations, and also extended to other NLGN2 associated proteins [e.g., α-neurexin (NRXN), gephyrin]. Midbrain SERT/NLGN2 interactions were found to be Ca(2+)-independent, supporting cis vs. trans-synaptic interactions, and were absent in hippocampal preparations, consistent with interactions arising in somatodendritic compartments. Dual color in situ hybridization confirmed co-expression of Tph2 and Nlgn2 mRNA in the dorsal raphe, with immunocytochemical studies confirming SERT:NLGN2 co-localization in raphe cell bodies but not axons. Consistent with correlative mRNA expression studies, loss of NLGN2 expression in Nlgn2 null mice produced significant reductions in midbrain and hippocampal SERT expression and function. Additionally, dorsal raphe 5-HT neurons from Nlgn2 null mice exhibit reduced excitability, a loss of GABAA receptor-mediated IPSCs, and increased 5-HT1A autoreceptor sensitivity. Finally, Nlgn2 null mice display significant changes in behaviors known to be responsive to SERT and/or 5-HT receptor manipulations. We discuss our findings in relation to the possible coordination of intrinsic and extrinsic regulation afforded by somatodendritic SERT:NLGN2 complexes.

The balancing act of GABAergic synapse organizers

GABA (γ-aminobutyric acid) is the main neurotransmitter at inhibitory synapses in the mammalian brain. It is essential for maintaining the excitation and inhibition (E/I) ratio, whose imbalance underlies various brain diseases. Emerging information about inhibitory synapse organizers provides a novel molecular framework for understanding E/I balance at the synapse, circuit, and systems levels. This review highlights recent advances in deciphering these components of the inhibitory synapse and their roles in the development, transmission, and circuit properties of inhibitory synapses. We also discuss how their dysfunction may lead to a variety of brain disorders, suggesting new therapeutic strategies based on balancing the E/I ratio.

KCC2 rescues functional deficits in human neurons derived from patients with Rett syndrome

Rett syndrome is a severe form of autism spectrum disorder, mainly caused by mutations of a single gene methyl CpG binding protein 2 (MeCP2) on the X chromosome. Patients with Rett syndrome exhibit a period of normal development followed by regression of brain function and the emergence of autistic behaviors. However, the mechanism behind the delayed onset of symptoms is largely unknown. Here we demonstrate that neuron-specific K(+)-Cl(-) cotransporter2 (KCC2) is a critical downstream gene target of MeCP2. We found that human neurons differentiated from induced pluripotent stem cells from patients with Rett syndrome showed a significant deficit in KCC2 expression and consequently a delayed GABA functional switch from excitation to inhibition. Interestingly, overexpression of KCC2 in MeCP2-deficient neurons rescued GABA functional deficits, suggesting an important role of KCC2 in Rett syndrome. We further identified that RE1-silencing transcriptional factor, REST, a neuronal gene repressor, mediates the MeCP2 regulation of KCC2. Because KCC2 is a slow onset molecule with expression level reaching maximum later in development, the functional deficit of KCC2 may offer an explanation for the delayed onset of Rett symptoms. Our studies suggest that restoring KCC2 function in Rett neurons may lead to a potential treatment for Rett syndrome.

Generation of Functional Inhibitory Synapses Incorporating Defined Combinations of GABA(A) or Glycine Receptor Subunits

Fast inhibitory neurotransmission in the brain is mediated by wide range of GABAA receptor (GABAAR) and glycine receptor (GlyR) isoforms, each with different physiological and pharmacological properties. Because multiple isoforms are expressed simultaneously in most neurons, it is difficult to define the properties of individual isoforms under synaptic stimulation conditions in vivo. Although recombinant expression systems permit the expression of individual isoforms in isolation, they require exogenous agonist application which cannot mimic the dynamic neurotransmitter profile characteristic of native synapses. We describe a neuron-HEK293 cell co-culture technique for generating inhibitory synapses incorporating defined combinations of GABAAR or GlyR subunits. Primary neuronal cultures, prepared from embryonic rat cerebral cortex or spinal cord, are used to provide presynaptic GABAergic and glycinergic terminals, respectively. When the cultures are mature, HEK293 cells expressing the subunits of interest plus neuroligin 2A are plated onto the neurons, which rapidly form synapses onto HEK293 cells. Patch clamp electrophysiology is then used to analyze the physiological and pharmacological properties of the inhibitory postsynaptic currents mediated by the recombinant receptors. The method is suitable for investigating the kinetic properties or the effects of drugs on inhibitory postsynaptic currents mediated by defined GABAAR or GlyR isoforms of interest, the effects of hereditary disease mutations on the formation and function of both types of synapses, and synaptogenesis and synaptic clustering mechanisms. The entire cell preparation procedure takes 2-5 weeks.

Evidence for Association of Cell Adhesion Molecules Pathway and NLGN1 Polymorphisms with Schizophrenia in Chinese Han Population

Multiple risk variants of schizophrenia have been identified by Genome-wide association studies (GWAS). As a complement for GWAS, previous pathway-based analysis has indicated that cell adhesion molecules (CAMs) pathway might be involved in the pathogenesis of schizophrenia. However, less replication studies have been reported. Our objective was to investigate the association between CAMs pathway and schizophrenia in the Chinese Han population. We first performed a pathway analysis utilizing our previous GWAS data. The CAMs pathway (hsa04514) was significantly associated with schizophrenia using hybrid gene set-based test (P = 1.03×10⁻¹⁰) and hypergeometric test (P = 5.04×10⁻⁶). Moreover, 12 genes (HLA-A, HLA-C, HLA-DOB, HLA-DPB1, HLA-DQA2, HLA-DRB1, MPZ, CD276, NLGN1, NRCAM, CLDN1 and ICAM3) were modestly significantly associated with schizophrenia (P<0.01). Then, we selected one promising gene neuroligin 1 (NLGN1) to further investigate the association between eight significant SNPs and schizophrenia in an independent sample (1814 schizophrenia cases and 1487 healthy controls). Our study showed that seven SNPs of NLGN1 and two haplotype blocks were significantly associated with schizophrenia. This association was confirmed by the results of combined analysis. Among them, SNP rs9835385 had the most significant association with schizophrenia (P = 2.83×10⁻⁷). Furthermore, in silico analysis we demonstrated that NLGN1 is preferentially expressed in human brain and SNP rs1488547 was related to the expression level. We validated the association of CAMs pathway with schizophrenia in pathway-level and identified one susceptibility gene NLGN1. Further investigation of the roles of CAMs pathway in the pathogenesis of schizophrenia is warranted.

Trans effects of chromosome aneuploidies on DNA methylation patterns in human Down syndrome and mouse models

Background

Trisomy 21 causes Down syndrome (DS), but the mechanisms by which the extra chromosome leads to deficient intellectual and immune function are not well understood.

Results

Here, we profile CpG methylation in DS and control cerebral and cerebellar cortex of adults and cerebrum of fetuses. We purify neuronal and non-neuronal nuclei and T lymphocytes and find biologically relevant genes with DS-specific methylation (DS-DM) in each of these cell types. Some genes show brain-specific DS-DM, while others show stronger DS-DM in T cells. Both 5-methyl-cytosine and 5-hydroxy-methyl-cytosine contribute to the DS-DM. Thirty percent of genes with DS-DM in adult brain cells also show DS-DM in fetal brains, indicating early onset of these epigenetic changes, and we find early maturation of methylation patterns in DS brain and lymphocytes. Some, but not all, of the DS-DM genes show differential expression. DS-DM preferentially affected CpGs in or near specific transcription factor binding sites (TFBSs), implicating a mechanism involving altered TFBS occupancy. Methyl-seq of brain DNA from mouse models with sub-chromosomal duplications mimicking DS reveals partial but significant overlaps with human DS-DM and shows that multiple chromosome 21 genes contribute to the downstream epigenetic effects.

Conclusions

These data point to novel biological mechanisms in DS and have general implications for trans effects of chromosomal duplications and aneuploidies on epigenetic patterning.

Electronic supplementary material

The online version of this article (doi:10.1186/s13059-015-0827-6) contains supplementary material, which is available to authorized users.

Practical Experience of the Application of a Weighted Burden Test to Whole Exome Sequence Data for Obesity and Schizophrenia

For biological and statistical reasons it makes sense to combine information from variants at the level of the gene. One may wish to give more weight to variants which are rare and those that are more likely to affect function. A combined weighting scheme, implemented in the SCOREASSOC program, was applied to whole exome sequence data for 1392 subjects with schizophrenia and 982 with obesity from the UK10K project. Results conformed fairly well with null hypothesis expectations and no individual gene was strongly implicated. However, a number of the higher ranked genes appear plausible candidates as being involved in one or other phenotype and may warrant further investigation. These include MC4R, NLGN2, CRP, DONSON, GTF3A, IL36B, ADCYAP1R1, ARSA, DLG1, SIK2, SLAIN1, UBE2Q2, ZNF507, CRHR1, MUSK, NSF, SNORD115, GDF3 and HIBADH. Some individual variants in these genes have different frequencies between cohorts and could be genotyped in additional subjects. For other genes, there is a general excess of variants at many different sites so attempts at replication would be more difficult. Overall, the weighted burden test provides a convenient method for using sequence data to highlight genes of interest.

Conditional neuroligin-2 knockout in adult medial prefrontal cortex links chronic changes in synaptic inhibition to cognitive impairments

Abnormal activity in the medial prefrontal cortex (mPFC) is consistently observed in neuropsychiatric disorders, but the mechanisms involved remain unclear. Chronic aberrant excitation and/or inhibition of mPFC neurons were proposed to cause cognitive impairments. However, direct evidence for this hypothesis is lacking because it is technically challenging to control synaptic properties in a chronic and locally restricted, yet specific, manner. Here, we generated conditional knockout (cKO) mice of neuroligin-2 (Nlgn2), a postsynaptic cell-adhesion molecule of inhibitory synapses linked to neuropsychiatric disorders. cKO of Nlgn2 in adult mPFC rendered Nlgn2 protein undetectable after already 2-3 weeks, but induced major reductions in synaptic inhibition after only 6-7 weeks, and caused parallel impairments in anxiety, fear memory and social interaction behaviors. Moreover, cKO of Nlgn2 severely impaired behavioral stimulation of immediate-early gene expression in the mPFC, suggesting that chronic reduction in synaptic inhibition uncoupled the mPFC from experience-dependent inputs. Our results indicate that Nlgn2 is required for continuous maintenance of inhibitory synapses in the adult mPFC, and that chronic impairment of local inhibition disengages the mPFC from its cognitive functions by partially uncoupling the mPFC from experience-induced inputs.

Neuroligin 2 deletion alters inhibitory synapse function and anxiety-associated neuronal activation in the amygdala

Neuroligin 2 (Nlgn2) is a synaptic adhesion protein that plays a central role in the maturation and function of inhibitory synapses. Nlgn2 mutations have been associated with psychiatric disorders such as schizophrenia, and in mice, deletion of Nlgn2 results in a pronounced anxiety phenotype. To date, however, the molecular and cellular mechanisms linking Nlgn2 deletion to psychiatric phenotypes remain completely unknown. The aim of this study was therefore to define the role of Nlgn2 in anxiety-related neural circuits. To this end, we used a combination of behavioral, immunohistochemical, and electrophysiological approaches in Nlgn2 knockout (KO) mice to expand the behavioral characterization of these mice and to assess the functional consequences of Nlgn2 deletion in the amygdala. Moreover, we investigated the differential activation of anxiety-related circuits in Nlgn2 KO mice using a cFOS activation assay following exposure to an anxiogenic stimulus. We found that Nlgn2 is present at the majority of inhibitory synapses in the basal amygdala, where its deletion affects postsynaptic structures specifically at perisomatic sites and leads to impaired inhibitory synaptic transmission. Following exposure to an anxiogenic environment, Nlgn2 KO mice show a robust anxiety phenotype as well as exacerbated induction of cFOS expression specifically in CaMKII-positive projection neurons, but not in parvalbumin- or somatostatin-positive interneurons. Our data indicate that Nlgn2 deletion predominantly affects inhibitory synapses onto projection neurons in basal amygdala, resulting in decreased inhibitory drive onto these neurons and leading to their excessive activation under anxiogenic conditions. This article is part of the Special Issue entitled 'Synaptopathy--from Biology to Therapy'.

Hippocampal neuroligin-2 links early-life stress with impaired social recognition and increased aggression in adult mice

Early-life stress is a key risk factor for the development of neuropsychiatric disorders later in life. Neuronal cell adhesion molecules have been strongly implicated in the pathophysiology of psychiatric disorders and in modulating social behaviors associated with these diseases. Neuroligin-2 is a synaptic cell adhesion molecule, located at the postsynaptic membrane of inhibitory GABAergic synapses, and is involved in synaptic stabilization and maturation. Alterations in neuroligin-2 expression have previously been associated with changes in social behavior linked to psychiatric disorders, including schizophrenia and autism. In this study, we show that early-life stress, induced by limited nesting and bedding material, leads to impaired social recognition and increased aggression in adult mice, accompanied by increased expression levels of hippocampal neuroligin-2. Viral overexpression of hippocampal neuroligin-2 in adulthood mimics early-life stress-induced alterations in social behavior and social cognition. Moreover, viral knockdown of neuroligin-2 in the adult hippocampus attenuates the early-life stress-induced behavioral changes. Our results highlight the importance of neuroligin-2 in mediating early-life stress effects on social behavior and social cognition and its promising role as a novel therapeutic target for neuropsychiatric disorders.

S-SCAM, a rare copy number variation gene, induces schizophrenia-related endophenotypes in transgenic mouse model

Accumulating genetic evidence suggests that schizophrenia (SZ) is associated with individually rare copy number variations (CNVs) of diverse genes, often specific to single cases. However, the causality of these rare mutations remains unknown. One of the rare CNVs found in SZ cohorts is the duplication of Synaptic Scaffolding Molecule (S-SCAM, also called MAGI-2), which encodes a postsynaptic scaffolding protein controlling synaptic AMPA receptor levels, and thus the strength of excitatory synaptic transmission. Here we report that, in a transgenic mouse model simulating the duplication conditions, elevation of S-SCAM levels in excitatory neurons of the forebrain was sufficient to induce multiple SZ-related endophenotypes. S-SCAM transgenic mice showed an increased number of lateral ventricles and a reduced number of parvalbumin-stained neurons. In addition, the mice exhibited SZ-like behavioral abnormalities, including hyperlocomotor activity, deficits in prepulse inhibition, increased anxiety, impaired social interaction, and working memory deficit. Notably, the S-SCAM transgenic mice showed a unique sex difference in showing these behavioral symptoms, which is reminiscent of human conditions. These behavioral abnormalities were accompanied by hyperglutamatergic function associated with increased synaptic AMPA receptor levels and impaired long-term potentiation. Importantly, reducing glutamate release by the group 2 metabotropic glutamate receptor agonist LY379268 ameliorated the working memory deficits in the transgenic mice, suggesting that hyperglutamatergic function underlies the cognitive functional deficits. Together, these results contribute to validate a causal relationship of the rare S-SCAM CNV and provide supporting evidence for the rare CNV hypothesis in SZ pathogenesis. Furthermore, the S-SCAM transgenic mice provide a valuable new animal model for studying SZ pathogenesis.

The association of GPR85 with PSD-95-neuroligin complex and autism spectrum disorder: a molecular analysis

Background

Autism spectrum disorder (ASD) has a complex genetic etiology. Some symptoms and mutated genes, including neuroligin (NLGN), neurexin (NRXN), and SH3 and multiple ankyrin repeat domains protein (SHANK), are shared by schizophrenia and ASD. Little is known about the molecular pathogenesis of ASD. One of the possible molecular pathogenesis is an imbalance of excitatory and inhibitory receptors linked with the NLGN-PSD-95-SHANK complex via postsynaptic density protein/Drosophila disc large tumor suppressor/zonula occludens-1 protein (PDZ) binding. In the present study, we focused on GPR85 as a candidate gene for ASD because the C-terminal amino acid sequence of GPR85 [Thr-Cys-Val-Ile (YCVI)] is classified as a type II PDZ-binding motif, and GPR85 is a risk factor for schizophrenia. GPR85 is an orphan receptor that regulates neural and synaptic plasticity and modulates diverse behaviors, including learning and memory. While searching for molecules that associate with GPR85, we found that GPR85 was associated with postsynaptic density protein (PSD)-95 linked with NLGN in the brain.

Methods

We examined the proteins that associate with the C-terminal sequence of GPR85 by pull-down assay and immunoblot analysis and searched for a mutation of the GPR85 gene in patients with ASD. We used immunostaining to examine the intracellular localization of mutated GPR85 and its influence on the morphology of cells and neurons.

Results

The C-terminal sequence of GPR85 interacted with PSD-95 at PDZ1, while NLGN interacted with PSD-95 at PDZ3. Two male patients with ASD from independent Japanese families possessed inherited missense mutations at conserved sites in GPR85: one had T1033C (M152T) and the other had G1239T (V221L). These mutations were located in a domain related to G protein interaction and signal transduction. In contrast to wild-type GPR85, mutated GPR85 was more preferentially accumulated, causing endoplasmic reticulum stress, and disturbed the dendrite formation of hippocampal neurons.

Conclusions

GPR85 associated with the PSD-95 linked with NLGN, which is related to ASD. GPR85 carrying the mutations detected in ASD patients disturbed dendrite formation that could be the candidate for molecular pathogenesis of ASD through the associated NLGN-PSD-95 receptor complex.

Electronic supplementary material

The online version of this article (doi:10.1186/s13229-015-0012-5) contains supplementary material, which is available to authorized users.

Excess of rare variants in genes that are key epigenetic regulators of spermatogenesis in the patients with non-obstructive azoospermia

Non-obstructive azoospermia (NOA), a severe form of male infertility, is often suspected to be linked to currently undefined genetic abnormalities. To explore the genetic basis of this condition, we successfully sequenced ~650 infertility-related genes in 757 NOA patients and 709 fertile males. We evaluated the contributions of rare variants to the etiology of NOA by identifying individual genes showing nominal associations and testing the genetic burden of a given biological process as a whole. We found a significant excess of rare, non-silent variants in genes that are key epigenetic regulators of spermatogenesis, such as BRWD1, DNMT1, DNMT3B, RNF17, UBR2, USP1 and USP26, in NOA patients (P = 5.5 × 10(-7)), corresponding to a carrier frequency of 22.5% of patients and 13.7% of controls (P = 1.4 × 10(-5)). An accumulation of low-frequency variants was also identified in additional epigenetic genes (BRDT and MTHFR). Our study suggested the potential associations of genetic defects in genes that are epigenetic regulators with spermatogenic failure in human.

Cation-chloride cotransporters in neuronal development, plasticity and disease

Electrical activity in neurons requires a seamless functional coupling between plasmalemmal ion channels and ion transporters. Although ion channels have been studied intensively for several decades, research on ion transporters is in its infancy. In recent years, it has become evident that one family of ion transporters, cation-chloride cotransporters (CCCs), and in particular K(+)-Cl(-) cotransporter 2 (KCC2), have seminal roles in shaping GABAergic signalling and neuronal connectivity. Studying the functions of these transporters may lead to major paradigm shifts in our understanding of the mechanisms underlying brain development and plasticity in health and disease.

Methamphetamine-induced sensitization is associated with alterations to the proteome of the prefrontal cortex: implications for the maintenance of psychotic disorders

Repeat administration of psychostimulants, such as methamphetamine, produces a progressive increase in locomotor activity (behavioral sensitization) in rodents that is believed to represent the underlying neurochemical changes driving psychoses. Alterations to the prefrontal cortex (PFC) are suggested to mediate the etiology and maintenance of these behavioral changes. As such, the aim of the current study was to investigate changes to protein expression in the PFC in male rats sensitized to methamphetamine using quantitative label-free shotgun proteomics. A methamphetamine challenge resulted in a significant sensitized locomotor response in methamphetamine pretreated animals compared to saline controls. Proteomic analysis revealed 96 proteins that were differentially expressed in the PFC of methamphetamine treated rats, with 20% of these being previously implicated in the neurobiology of schizophrenia in the PFC. We identified multiple biological functions in the PFC that appear to be commonly altered across methamphetamine-induced sensitization and schizophrenia, and these include synaptic regulation, protein phosphatase signaling, mitochondrial function, and alterations to the inhibitory GABAergic network. These changes could inform how alterations to the PFC could underlie the cognitive and behavioral dysfunction commonly seen across psychoses and places such biological changes as potential mediators in the maintenance of psychosis vulnerability.

Drosophila neuroligin3 regulates neuromuscular junction development and synaptic differentiation

Neuroligins (Nlgs) are a family of cell adhesion molecules thought to be important for synapse maturation and function. Mammalian studies have shown that different Nlgs have different roles in synaptic maturation and function. In Drosophila melanogaster, the roles of Drosophila neuroligin1 (DNlg1), neuroligin2, and neuroligin4 have been examined. However, the roles of neuroligin3 (dnlg3) in synaptic development and function have not been determined. In this study, we used the Drosophila neuromuscular junctions (NMJs) as a model system to investigate the in vivo role of dnlg3. We showed that DNlg3 was expressed in both the CNS and NMJs where it was largely restricted to the postsynaptic site. We generated dnlg3 mutants and showed that these mutants exhibited an increased bouton number and reduced bouton size compared with the wild-type (WT) controls. Consistent with alterations in bouton properties, pre- and postsynaptic differentiations were affected in dnlg3 mutants. This included abnormal synaptic vesicle endocytosis, increased postsynaptic density length, and reduced GluRIIA recruitment. In addition to impaired synaptic development and differentiation, we found that synaptic transmission was reduced in dnlg3 mutants. Altogether, our data showed that DNlg3 was required for NMJ development, synaptic differentiation, and function.

The one and the many: effects of the cell adhesion molecule pathway on neuropsychological function in psychosis

BACKGROUND

Genetic studies of single gene variants have been criticized as providing a simplistic characterization of the genetic basis of illness risk that ignores the effects of other variants within the same biological pathways. Of candidate biological pathways for schizophrenia (SZ), the cell adhesion molecule (CAM) pathway has repeatedly been linked to both psychosis and neurocognitive dysfunction. Here we tested, using risk allele scores derived from the Schizophrenia Psychiatric Genome-Wide Association Study Consortium (PGC-SCZ), whether alleles within the CAM pathway were correlated with poorer neuropsychological function in patients.

METHOD

In total, 424 patients with psychosis were assessed in areas of cognitive ability typically found to be impaired in SZ: intelligence quotient, memory, working memory and attentional control. CAM pathway genes were identified using the Kyoto Encyclopedia of Genes and Genomes (KEGG) database. Alleles within these genes identified as significantly associated with SZ risk in the PGC-SCZ were then used to calculate a CAM pathway-based polygenic risk allele score for each patient and these scores were tested for association with cognitive ability.

RESULTS

Increased CAM pathway polygenic risk scores were significantly associated with poorer performance on measures of memory and attention, explaining 1-3% of variation on these measures. Notably, the most strongly associated single nucleotide polymorphism (SNP) in the CAM pathway (rs9272105 within HLA-DQA1) explained a similar amount of variance in attentional control, but not memory, as the polygenic risk analysis.

CONCLUSIONS

These data support a role for the CAM pathway in cognitive function, both at the level of individual SNPs and the wider pathway. In so doing these data highlight the value of pathway-based polygenic risk score studies as well as single gene studies for understanding SZ-associated deficits in cognition.

Identification of gene ontologies linked to prefrontal-hippocampal functional coupling in the human brain

Functional interactions between the dorsolateral prefrontal cortex and hippocampus during working memory have been studied extensively as an intermediate phenotype for schizophrenia. Coupling abnormalities have been found in patients, their unaffected siblings, and carriers of common genetic variants associated with schizophrenia, but the global genetic architecture of this imaging phenotype is unclear. To achieve genome-wide hypothesis-free identification of genes and pathways associated with prefrontal-hippocampal interactions, we combined gene set enrichment analysis with whole-genome genotyping and functional magnetic resonance imaging data from 269 healthy German volunteers. We found significant enrichment of the synapse organization and biogenesis gene set. This gene set included known schizophrenia risk genes, such as neural cell adhesion molecule (NRCAM) and calcium channel, voltage-dependent, beta 2 subunit (CACNB2), as well as genes with well-defined roles in neurodevelopmental and plasticity processes that are dysfunctional in schizophrenia and have mechanistic links to prefrontal-hippocampal functional interactions. Our results demonstrate a readily generalizable approach that can be used to identify the neurogenetic basis of systems-level phenotypes. Moreover, our findings identify gene sets in which genetic variation may contribute to disease risk through altered prefrontal-hippocampal functional interactions and suggest a link to both ongoing and developmental synaptic plasticity.

Impaired hippocampal neuroligin-2 function by chronic stress or synthetic peptide treatment is linked to social deficits and increased aggression

Neuroligins (NLGNs) are cell adhesion molecules that are important for proper synaptic formation and functioning, and are critical regulators of the balance between neural excitation/inhibition (E/I). Mutations in NLGNs have been linked to psychiatric disorders in humans involving social dysfunction and are related to similar abnormalities in animal models. Chronic stress increases the likelihood for affective disorders and has been shown to induce changes in neural structure and function in different brain regions, with the hippocampus being highly vulnerable to stress. Previous studies have shown evidence of chronic stress-induced changes in the neural E/I balance in the hippocampus. Therefore, we hypothesized that chronic restraint stress would lead to reduced hippocampal NLGN-2 levels, in association with alterations in social behavior. We found that rats submitted to chronic restraint stress in adulthood display reduced sociability and increased aggression. This occurs along with a reduction of NLGN-2, but not NLGN-1 expression (as shown with western blot, immunohistochemistry, and electron microscopy analyses), throughout the hippocampus and detectable in different layers of the CA1, CA3, and DG subfields. Furthermore, using synthetic peptides that comprise sequences in either NLGN-1 (neurolide-1) or NLGN-2 (neurolide-2) involved in the interaction with their presynaptic partner neurexin (NRXN)-1, intra-hippocampal administration of neurolide-2 led also to reduced sociability and increased aggression. These results highlight hippocampal NLGN-2 as a key molecular substrate regulating social behaviors and underscore NLGNs as promising targets for the development of novel drugs for the treatment of dysfunctional social behaviors.

Quantitative trait loci mapping and gene network analysis implicate protocadherin-15 as a determinant of brain serotonin transporter expression

Presynaptic serotonin (5-hydroxytryptamine, 5-HT) transporters (SERT) regulate 5-HT signaling via antidepressant-sensitive clearance of released neurotransmitter. Polymorphisms in the human SERT gene (SLC6A4) have been linked to risk for multiple neuropsychiatric disorders, including depression, obsessive-compulsive disorder and autism. Using BXD recombinant inbred mice, a genetic reference population that can support the discovery of novel determinants of complex traits, merging collective trait assessments with bioinformatics approaches, we examine phenotypic and molecular networks associated with SERT gene and protein expression. Correlational analyses revealed a network of genes that significantly associated with SERT mRNA levels. We quantified SERT protein expression levels and identified region- and gender-specific quantitative trait loci (QTLs), one of which associated with male midbrain SERT protein expression, centered on the protocadherin-15 gene (Pcdh15), overlapped with a QTL for midbrain 5-HT levels. Pcdh15 was also the only QTL-associated gene whose midbrain mRNA expression significantly associated with both SERT protein and 5-HT traits, suggesting an unrecognized role of the cell adhesion protein in the development or function of 5-HT neurons. To test this hypothesis, we assessed SERT protein and 5-HT traits in the Pcdh15 functional null line (Pcdh15(av-) (3J) ), studies that revealed a strong, negative influence of Pcdh15 on these phenotypes. Together, our findings illustrate the power of multidimensional profiling of recombinant inbred lines in the analysis of molecular networks that support synaptic signaling, and that, as in the case of Pcdh15, can reveal novel relationships that may underlie risk for mental illness.

Neuroligin 2 is expressed in synapses established by cholinergic cells in the mouse brain

Neuroligin 2 is a postsynaptic protein that plays a critical role in the maturation and proper function of GABAergic synapses. Previous studies demonstrated that deletion of neuroligin 2 impaired GABAergic synaptic transmission, whereas its overexpression caused increased inhibition, which suggest that its presence strongly influences synaptic function. Interestingly, the overexpressing transgenic mouse line showed increased anxiety-like behavior and other behavioral phenotypes, not easily explained by an otherwise strengthened GABAergic transmission. This suggested that other, non-GABAergic synapses may also express neuroligin 2. Here, we tested the presence of neuroligin 2 at synapses established by cholinergic neurons in the mouse brain using serial electron microscopic sections double labeled for neuroligin 2 and choline acetyltransferase. We found that besides GABAergic synapses, neuroligin 2 is also present in the postsynaptic membrane of cholinergic synapses in all investigated brain areas (including dorsal hippocampus, somatosensory and medial prefrontal cortices, caudate putamen, basolateral amygdala, centrolateral thalamic nucleus, medial septum, vertical- and horizontal limbs of the diagonal band of Broca, substantia innominata and ventral pallidum). In the hippocampus, the density of neuroligin 2 labeling was similar in GABAergic and cholinergic synapses. Moreover, several cholinergic contact sites that were strongly labeled with neuroligin 2 did not resemble typical synapses, suggesting that cholinergic axons form more synaptic connections than it was recognized previously. We showed that cholinergic cells themselves also express neuroligin 2 in a subset of their input synapses. These data indicate that mutations in human neuroligin 2 gene and genetic manipulations of neuroligin 2 levels in rodents will potentially cause alterations in the cholinergic system as well, which may also have a profound effect on the functional properties of brain circuits and behavior.

Unexpected association of the "inhibitory" neuroligin 2 with excitatory PSD95 in neuropathic pain

In the spinal nerve ligation (SNL) model of neuropathic pain, synaptic plasticity shifts the excitation/inhibition balance toward excitation in the spinal dorsal horn. We investigated the deregulation of the synaptogenic neuroligin (NL) molecules, whose NL1 and NL2 isoforms are primarily encountered at excitatory and inhibitory synapses, respectively. In the dorsal horn of SNL rats, NL2 was overexpressed whereas NL1 remained unchanged. In control animals, intrathecal injections of small interfering RNA (siRNA) targeting NL2 increased mechanical sensitivity, which confirmed the association of NL2 with inhibition. By contrast, siRNA application produced antinociceptive effects in SNL rats. Regarding NL partners, expression of the excitatory postsynaptic scaffolding protein PSD95 unexpectedly covaried with NL2 overexpression, and NL2/PSD95 protein interaction and colocalization increased. Expression of the inhibitory scaffolding protein gephyrin remained unchanged, indicating a partial change in NL2 postsynaptic partners in SNL rats. This phenomenon appears to be specific to the NL2(-) isoform. Our data showed unexpected upregulation and pronociceptive effects of the "inhibitory" NL2 in neuropathic pain, suggesting a functional shift of NL2 from inhibition to excitation that changed the synaptic ratio toward higher excitation.

Exonic resequencing of the DLGAP3 gene as a candidate gene for schizophrenia

We resequenced the exonic regions of the DLGAP3 gene, which encodes SAP90/PSD95-associated protein 3, in 215 schizophrenic patients and 215 non-psychotic controls. Seven known single-nucleotide polymorphisms (SNPs) were identified, but not associated with schizophrenia. Nevertheless, we identified several rare missense mutations and some of them might be associated with the pathogenesis of schizophrenia.

Altered pancreatic islet function and morphology in mice lacking the Beta-cell surface protein neuroligin-2

Neuroligin-2 is a transmembrane, cell-surface protein originally identified as an inhibitory synapse-associated protein in the central nervous system. Neuroligin-2 is also present on the pancreatic beta-cell surface, and there it engages in transcellular interactions that drive functional maturation of the insulin secretory machinery; these are necessary for normal insulin secretion. The effects of neuroligin-2 deficiency on brain and neuronal function and morphology and on behavior and coordination have been extensively characterized using neuroligin-2 knockout mice. The effects of absent neuroligin-2 expression on islet development and function, however, are unknown. Here, to help test whether neuroligin-2 is necessary for normal islet development, we characterized islet morphology in mice lacking neuroligin-2. To test whether–as predicted by our earlier co-culture studies–absence of neuroligin-2 impairs beta cell function, we compared glucose-stimulated insulin secretion by islets from mutant and wild-type mice. Our results show that while islets from neuroligin-2-deficient mice do not to appear to differ architecturally from wild-type islets, they are smaller, fewer in number, and contain beta cells with lower insulin content. Evaluation of transcript levels suggests that upregulation of neuroligin-1 helps compensate for loss of neuroligin-2. Surprisingly, under both basal and stimulating glucose levels, isolated islets from the knockout mice secreted more of their intracellular insulin content. Rat islets with shRNA-mediated neuroligin-2 knockdown also exhibited increased insulin secretion. Neurexin transcript levels were lower in the knockout mice and, consistent with our prior finding that neurexin is a key constituent of the insulin granule docking machinery, insulin granule docking was reduced. These results indicate that neuroligin-2 is not necessary for the formation of pancreatic islets but that neuroligin-2 influences islet size and number. Neuroligin-2–perhaps through its effects on the expression and/or activity of its binding partner neurexin–promotes insulin granule docking, a known constraint on insulin secretion.

An unexpected role of neuroligin-2 in regulating KCC2 and GABA functional switch

BACKGROUND

GABAA receptors are ligand-gated Cl- channels, and the intracellular Cl- concentration governs whether GABA function is excitatory or inhibitory. During early brain development, GABA undergoes functional switch from excitation to inhibition: GABA depolarizes immature neurons but hyperpolarizes mature neurons due to a developmental decrease of intracellular Cl- concentration. This GABA functional switch is mainly mediated by the up-regulation of KCC2, a potassium-chloride cotransporter that pumps Cl- outside neurons. However, the upstream factor that regulates KCC2 expression is unclear.

RESULTS

We report here that KCC2 is unexpectedly regulated by neuroligin-2 (NL2), a cell adhesion molecule specifically localized at GABAergic synapses. The expression of NL2 precedes that of KCC2 in early postnatal development. Upon knockdown of NL2, the expression level of KCC2 is significantly decreased, and GABA functional switch is significantly delayed during early development. Overexpression of shRNA-proof NL2 rescues both KCC2 reduction and delayed GABA functional switch induced by NL2 shRNAs. Moreover, NL2 appears to be required to maintain GABA inhibitory function even in mature neurons, because knockdown NL2 reverses GABA action to excitatory. Gramicidin-perforated patch clamp recordings confirm that NL2 directly regulates the GABA equilibrium potential. We further demonstrate that knockdown of NL2 decreases dendritic spines through down-regulating KCC2.

CONCLUSIONS

Our data suggest that in addition to its conventional role as a cell adhesion molecule to regulate GABAergic synaptogenesis, NL2 also regulates KCC2 to modulate GABA functional switch and even glutamatergic synapses. Therefore, NL2 may serve as a master regulator in balancing excitation and inhibition in the brain.

Specific trans-synaptic interaction with inhibitory interneuronal neurexin underlies differential ability of neuroligins to induce functional inhibitory synapses

Synaptic transmission depends on the matching and alignment of presynaptically released transmitters and postsynaptic neurotransmitter receptors. Neuroligin (NL) and Neurexin (Nrxn) proteins are trans-synaptic adhesion molecules that are important in validation and maturation of specific synapses. NL isoforms NL1 and NL2 have specific functional roles in excitatory and inhibitory synapses, respectively, but the molecular basis behind this distinction is still unclear. We show here that the extracellular domain of NL2 confers its unique ability to enhance inhibitory synaptic function when overexpressed in rat hippocampal pyramidal neurons, whereas NL1 normally only promotes excitatory synapses. This specificity is conferred by presynaptic Nrxn isoforms, as NL1 can also induce functional inhibitory synapse connections when the presynaptic interneurons ectopically express an Nrxn isoform that binds to NL1. Our results indicate that trans-synaptic interaction with differentially expressed presynaptic Nrxns underlies the distinct functions of NL1 and NL2, and is sufficient to induce functional inhibitory synapse formation.

Hippocampal neuroligin-2 overexpression leads to reduced aggression and inhibited novelty reactivity in rats

Disturbances of the excitation/inhibition (E/I) balance in the brain were recently suggested as potential factors underlying disorders like autism and schizophrenia resulting in associated behavioral alterations including changes in social and emotional behavior as well as abnormal aggression. Neuronal cell adhesion molecules (nCAMs) and mutations in these genes were found to be strongly implicated in the pathophysiology of these disorders. Neuroligin2 (nlgn2) is a postsynaptic cell adhesion molecule, which is predominantly expressed at inhibitory synapses and required for synapse specification and stabilization. Changes in the expression of nlgn2 were shown to result in alterations of social behavior as well as altered inhibitory synaptic transmission, hence modifying the E/I balance. In our study, we focused on the role of nlgn2 in the dorsal hippocampus in the regulation of emotional and social behaviors. To this purpose, we injected an AAV construct overexpressing nlgn2 in the hippocampus of rats and investigated the effects on behavior and on markers for the E/I ratio. We could show an increase in GAD65, a GABA-synthesizing protein in neuronal terminals, and furthermore, reduced exploration of novel stimuli and less offensive behavior. Our data suggest nlgn2 in the hippocampus to be strongly implicated in maintaining the E/I balance in the brain and thereby modulating social and emotional behavior.

Interaction between autism-linked MDGAs and neuroligins suppresses inhibitory synapse development

Rare variants in MDGAs (MAM domain-containing glycosylphosphatidylinositol anchors), including multiple protein-truncating deletions, are linked to autism and schizophrenia, but the function of these genes is poorly understood. Here, we show that MDGA1 and MDGA2 bound to neuroligin-2 inhibitory synapse-organizing protein, also implicated in neurodevelopmental disorders. MDGA1 inhibited the synapse-promoting activity of neuroligin-2, without altering neuroligin-2 surface trafficking, by inhibiting interaction of neuroligin-2 with neurexin. MDGA binding and suppression of synaptogenic activity was selective for neuroligin-2 and not neuroligin-1 excitatory synapse organizer. Overexpression of MDGA1 in cultured rat hippocampal neurons reduced inhibitory synapse density without altering excitatory synapse density. Furthermore, RNAi-mediated knockdown of MDGA1 selectively increased inhibitory but not excitatory synapse density. These results identify MDGA1 as one of few identified negative regulators of synapse development with a unique selectivity for inhibitory synapses. These results also place MDGAs in the neurexin-neuroligin synaptic pathway implicated in neurodevelopmental disorders and support the idea that an imbalance between inhibitory and excitatory synapses may contribute to these disorders.

The C allele of synonymous SNP (rs1142636, Asn170Asn) in SYN1 is a risk factor for the susceptibility of Korean female schizophrenia

OBJECTIVE

The aim of this study was to investigate the association between the exonic single nucleotide polymorphisms (SNPs) of synapsin I (SYN1) (rs1142636, Asn170Asn, Xp11.23) and SYN2 (rs2289708, 3'-untranslated region, 3p25) in schizopherenia.

METHODS

Two hundred eighty six schizophrenia patients and 304 control subjects were recruited. SNPs with a know heterozygosity and minor allele frequency (MAF) > 0.1 in Asian populations were selected and genotyped by direct sequencing.

RESULTS

The allelic frequencies of rs1142636 (SYN1) were associated with schizophrenia (P < 0.05), respectively. The allelic frequency of rs1142636 in all subjects was associated with schizophrenia [P = 0.000059, OR = 2.17 (95% CI = 1.47-3.18)]. The C allele frequency of rs1142636 was higher in schizophrenia (20.8%) than that in controls (10.8%). In the analysis of gender, the allelic frequency of rs1142636 was also strongly associated with female schizophrenia [P = 0.0001, OR = 2.65 (95% CI = 1.61-4.36)], but not with male schizophrenia. The C allele frequency of rs1142636 was higher in female schizophrenia (22.2%) than that in female controls (9.7%). The rs2289708 SNP (SYN2) did not show any association between schizophrenia and controls.

CONCLUSIONS

These results suggest that the C allele of a synonymous SNP (rs1142636, Asn170Asn, Xp11.23) in SYN1 may be a risk factor for the susceptibility of Koreran female schizophrenia.

Developmental delays and reduced pup ultrasonic vocalizations but normal sociability in mice lacking the postsynaptic cell adhesion protein neuroligin2

Mutations in neurexin and neuroligin genes have been associated with neurodevelopmental disabilities including autism. Autism spectrum disorder is diagnosed by aberrant reciprocal social interactions, deficits in social communication, and repetitive, stereotyped patterns of behaviors, along with narrow restricted interests. Mouse models have been successfully used to study physiological and behavioral outcomes of mutations in the trans-synaptic neurexin-neuroligin complex. To further understand the behavioral consequences of Neuroligin2 (NLGN2) mutations, we assessed several behavioral phenotypes relevant to autism in neuroligin2 null (Nlgn2(-/-)), heterozygote (Nlgn2(+/-)), and wildtype (Nlgn2(+/+)) littermate control mice. Reduced breeding efficiency and high reactivity to handling was observed in Nlgn2(-/-) mice, resulting in low numbers of adult mice available for behavioral assessment. Consistent with previous findings, Nlgn2(-/-) mice displayed normal social behaviors, concomitant with reduced exploratory activity, impaired rotarod performance, and delays on several developmental milestones. No spontaneous stereotypies or repetitive behaviors were detected. Acoustic, tactile, and olfactory sensory information processing as well as sensorimotor gating were not affected. Nlgn2(-/-) pups isolated from mother and littermates emitted fewer ultrasonic vocalizations and spent less time calling than Nlgn2(+/+) littermate controls. The present findings add to the growing literature on the role of neurexins and neuroligins in physiology and behavior relevant to neurodevelopmental disorders.

γ-Aminobutyric acid type A (GABAA) receptor α subunits play a direct role in synaptic versus extrasynaptic targeting

GABA(A) receptors (GABA(A)-Rs) are localized at both synaptic and extrasynaptic sites, mediating phasic and tonic inhibition, respectively. Previous studies suggest an important role of γ2 and δ subunits in synaptic versus extrasynaptic targeting of GABA(A)-Rs. Here, we demonstrate differential function of α2 and α6 subunits in guiding the localization of GABA(A)-Rs. To study the targeting of specific subtypes of GABA(A)-Rs, we used a molecularly engineered GABAergic synapse model to precisely control the GABA(A)-R subunit composition. We found that in neuron-HEK cell heterosynapses, GABAergic events mediated by α2β3γ2 receptors were very fast (rise time ∼2 ms), whereas events mediated by α6β3δ receptors were very slow (rise time ∼20 ms). Such an order of magnitude difference in rise time could not be attributed to the minute differences in receptor kinetics. Interestingly, synaptic events mediated by α6β3 or α6β3γ2 receptors were significantly slower than those mediated by α2β3 or α2β3γ2 receptors, suggesting a differential role of α subunit in receptor targeting. This was confirmed by differential targeting of the same δ-γ2 chimeric subunits to synaptic or extrasynaptic sites, depending on whether it was co-assembled with the α2 or α6 subunit. In addition, insertion of a gephyrin-binding site into the intracellular domain of α6 and δ subunits brought α6β3δ receptors closer to synaptic sites. Therefore, the α subunits, together with the γ2 and δ subunits, play a critical role in governing synaptic versus extrasynaptic targeting of GABA(A)-Rs, possibly through differential interactions with gephyrin.