Project description:Synapse formation is a dynamic process essential for neuronal circuit development and maturation. At the synaptic cleft, trans-synaptic protein-protein interactions constitute major biological determinants of proper synapse efficacy. The balance of excitatory and inhibitory synaptic transmission (E-I balance) stabilizes synaptic activity and its dysregulation has been implicated in neurodevelopmental disorders including autism spectrum disorders. However, the molecular mechanisms underlying E-I balance remains to be elucidated. Here, we investigate Neuroligin (Nlgn) genes which encode a family of postsynaptic adhesion molecules that shape excitatory and inhibitory synaptic function. We identified that NLGN3 protein differentially regulates inhibitory synaptic transmission in a splice isoform-dependent manner in hippocampal CA1 synapses. Distinct subcellular localization patterns of NLGN3 isoforms contribute to the functional differences observed among splice variants. Finally, our single-cell sequencing analysis reveals that Nlgn1 and Nlgn3 are the major Nlgn genes and that Nlgn splice isoforms are highly diverse in CA1 pyramidal neurons.
Project description:Synapse formation is a dynamic process essential for the development and maturation of the neuronal circuitry in the brain. At the synaptic cleft, trans-synaptic protein-protein interactions are major biological determinants of proper synapse efficacy. The balance of excitatory and inhibitory synaptic transmission (E-I balance) stabilizes synaptic activity, and dysregulation of the E-I balance has been implicated in neurodevelopmental disorders, including autism spectrum disorders. However, the molecular mechanisms underlying the E-I balance remain to be elucidated. Here, using single-cell transcriptomics, immunohistochemistry, and electrophysiology approaches to murine CA1 pyramidal neurons obtained from organotypic hippocampal slice cultures, we investigate neuroligin (Nlgn) genes that encode a family of postsynaptic adhesion molecules known to shape excitatory and inhibitory synaptic function. We demonstrate that the NLGN3 protein differentially regulates inhibitory synaptic transmission in a splice isoform-dependent manner at hippocampal CA1 synapses. We also found that distinct subcellular localizations of the NLGN3 isoforms contribute to the functional differences observed among these isoforms. Finally, results from single-cell RNA-Seq analyses revealed that Nlgn1 and Nlgn3 are the major murine Nlgn genes and that the expression levels of the Nlgn splice isoforms are highly diverse in CA1 pyramidal neurons. Our results delineate isoform-specific effects of Nlgn genes on the E-I balance in the murine hippocampus.
Project description:Loh KH, Stawski PS, Draycott AS, Udeshi ND, Lehrman EK, Wilton DK, Svinkina T, Deerinck TJ, Ellisman MH, Stevens B, Carr SA, Ting AY. Cell 2016 Excitatory synapses are connections between neurons that promote the propagation of action potentials while inhibitory synapses repress them. Normal brain function relies on the careful balance of these antagonistic connections, which occur via molecularly distinct synaptic clefts. Understanding how this is
achieved relies on knowledge of their protein compositions, yet the clefts remain uncharacterized because they cannot be isolated biochemically. Here, we mapped the proteomes of two of the most common excitatory and inhibitory synaptic clefts in living neurons, using a spatially restricted enzymatic tagging strategy. These proteomes reveal dozens of novel synaptic candidates, and assign numerous known synaptic proteins to a specific cleft type. The molecular differentiation of each cleft allowed us to identify Mdga2 as a specificity factor regulating the presynaptic neurotransmitter recruiting activity of Neuroligin-2 at inhibitory synapses.
Project description: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 αNrxn1 and βNrxn3 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 αNrx1+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.
Project description:The autism-associated synaptic-adhesion gene Neuroligin-4 (NLGN4) is poorly conserved evolutionarily, limiting conclusions from Nlgn4 mouse models for human cells. Here, we show that the cellular and subcellular expression of human and murine Neuroligin-4 differ, with human Neuroligin-4 primarily expressed in cerebral cortex and localized to excitatory synapses. Overexpression of NLGN4 in human neurons resulted in an increase in excitatory synapse numbers but a remarkable decrease in synaptic strength. Human neurons carrying the syndromic autism mutation NLGN4-R704C also formed more excitatory synapses but with increased functional synaptic transmission due to a postsynaptic mechanism, while genetic loss of NLGN4 did not significantly affect synapses in the human neurons analyzed. Thus, the NLGN4-R704C mutation represents a change of function mutation. Our work reveals contrasting roles of NLGN4 in human and mouse neurons, suggesting human evolution has impacted even fundamental cell biological processes generally assumed to be highly conserved.
Project description:Synaptic dysfunction represents a key pathophysiology in neurodevelopmental disorders such as autism spectrum disorder (ASD). Rare mutation R451C in human Neuroligin 3 (NLGN3, encoded by X-linked gene NLGN3), a cell adhesion molecule essential for synapse formation, has been linked to ASD. Despite success in recapitulating the social interaction behavioral deficits and the underlying synaptic abnormalities in mouse model, the impact of NLGN3 R451C on the human neuronal system remains elusive. Here, we generated isogenic knock-in human pluripotent stem cell lines harboring NLGN3 R451C allele and examined its impact on synaptic transmission. Analysis of co-cultured excitatory and inhibitory induced neurons (iNs) with mutation revealed an augmentation in excitatory synaptic strength comparing to isogenic control, but not in inhibitory synaptic transmission. Consistently, the augmentation in excitatory transmission was confirmed in iNs transplanted into mouse forebrain. Using single-cell RNA seq on co-cultured excitatory and inhibitory iNs, we identified differential expression genes (DEGs) and found NLGN3 R451C alters gene networks associated with synaptic transmission. Gene ontology and enrichment analysis revealed convergent gene networks associated with ASD and other mental disorders. Our finding suggests that the NLGN3 R451C mutation could preferentially impact excitatory neurons, which causes overall network properties changes and excitation-inhibition imbalance related to mental disorders.
Project description:Identifying causes of sporadic intellectual disability remains a considerable medical challenge. Here, we demonstrate that null mutations in the NONO gene, a member of the Drosophila Behavior Human Splicing (DBHS) protein family, are a novel cause of X-linked syndromic intellectual disability. Comparing humans to Nono-deficient mice revealed related behavioral and craniofacial anomalies, as well as global transcriptional dysregulation. Nono-deficient mice also showed deregulation of a large number of synaptic transcripts, causing a disorganization of inhibitory synapses, with impaired postsynaptic scaffolding of gephyrin. Alteration of gephyrin clustering could be rescued by over-expression of Gabra2 in NONO-compromised neurons. These findings link NONO to intellectual disability and first highlight the key role of DBHS proteins in functional organization of GABAergic synapses.
Project description:Identifying causes of sporadic intellectual disability remains a considerable medical challenge. Here, we demonstrate that null mutations in the NONO gene, a member of the Drosophila Behavior Human Splicing (DBHS) protein family, are a novel cause of X-linked syndromic intellectual disability. Comparing humans to Nono-deficient mice revealed related behavioral and craniofacial anomalies, as well as global transcriptional dysregulation. Nono-deficient mice also showed deregulation of a large number of synaptic transcripts, causing a disorganization of inhibitory synapses, with impaired postsynaptic scaffolding of gephyrin. Alteration of gephyrin clustering could be rescued by over-expression of Gabra2 in NONO-compromised neurons. These findings link NONO to intellectual disability and first highlight the key role of DBHS proteins in functional organization of GABAergic synapses.