Dendritic Spine Development Research Articles

Functional analysis and signaling pathway enrichment analysis of genes associated with Alzheimer’s disease and Parkinson’s disease

We identified significant functions of susceptibility-genes and performed an analysis of pathway enrichment for Alzheimer’s disease, Parkinson’s disease and for both of them. Genes were extracted from a Catalog of Published Genome-Wide Association Studies (GWAS). We uploaded genes into Cytoscape version 3.2.1. ClueGO plugin was used for functional and pathway enrichment analysis of genes based on the hypergeometric test. Two databases, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway and REACTOME, were selected for analysis. The identified susceptibility genes are involved in the synthesis regulation and accumulation of toxic proteins, β -amyloid and α -synuclein, and lead to apoptosis of neurons. We have defined 14 shared functions: collagen catabolic process, cellular response to retinoic acid, regulation of calcium-mediated signaling, negative regulation of cell projection organization, negative regulation of neuron projection development, glial cell activation, microglial cell activation, macrophage activation, regulation of cholesterol metabolism, clathrin-mediated endocytosis, regulation of protein oligomerization, regulation of dendritic spine development, kinesin binding and clathrin binding. Also, we have defined 3 shared signaling pathways: trans-Golgi Network Vesicle Budding, Clathrin derived vesicle budding, Intestinal immune network for IgA production. These pathways contain genes susceptible to Alzheimer’s disease and Parkinson’s disease. The results suggest the metabolic, neuronal and immunological factors participate in the development of Parkinson’s disease and Alzheimer’s disease.

Increased expression of schizophrenia-associated gene C4 leads to hypoconnectivity of prefrontal cortex and reduced social interaction.

Schizophrenia is a severe mental disorder with an unclear pathophysiology. Increased expression of the immune gene C4 has been linked to a greater risk of developing schizophrenia; however, it is not known whether C4 plays a causative role in this brain disorder. Using confocal imaging and whole-cell electrophysiology, we demonstrate that overexpression of C4 in mouse prefrontal cortex neurons leads to perturbations in dendritic spine development and hypoconnectivity, which mirror neuropathologies found in schizophrenia patients. We find evidence that microglia-mediated synaptic engulfment is enhanced with increased expression of C4. We also show that C4-dependent circuit dysfunction in the frontal cortex leads to decreased social interactions in juvenile and adult mice. These results demonstrate that increased expression of the schizophrenia-associated gene C4 causes aberrant circuit wiring in the developing prefrontal cortex and leads to deficits in juvenile and adult social behavior, suggesting that altered C4 expression contributes directly to schizophrenia pathogenesis.

Vasodilator-stimulated phosphoprotein (VASP) is recruited into dendritic spines via G-actin-dependent mechanism and contributes to spine enlargement and stabilization.

Actin organization and dynamics are modulated by diverse actin regulators during dendritic spine development. To understand the molecular network that regulates actin organization and spine morphology, it is important to investigate dynamic redistribution of actin regulators during spine development. One of the actin regulators, vasodilator-stimulated phosphoprotein (VASP), has multiple functions in actin regulation and is known to regulate spine morphology. However, dynamics and temporal regulation of VASP during spine development have not been clarified. In this study, we performed time-lapse imaging of mouse hippocampal dissociated neurons to analyse the change in localization of VASP during spine development. We found that accumulation of VASP within spines precedes the start of persistent F-actin increase, which are temporally coupled with spine enlargement. Using domain deletion or mutation constructs of VASP, we revealed that the interaction with G-actin is important for the preceding accumulation of VASP. Furthermore, we showed that accumulation of VASP contributes to actin enrichment within spines and stabilization of spine morphology by dominant negative experiments. These data suggest that G-actin-dependent VASP recruitment has dual functions in spine development, enlargement and stabilization, through the interaction with actin and other cytoskeletal regulators.

Leptin Controls Glutamatergic Synaptogenesis and NMDA-Receptor Trafficking via Fyn Kinase Regulation of NR2B.

Activation of the leptin receptor, LepRb, by the adipocytokine/neurotrophic factor leptin in the central nervous system has procognitive and antidepressive effects. Leptin has been shown to increase glutamatergic synaptogenesis in multiple brain regions. In contrast, mice that have a mutation in the LepRb gene show abnormal synapse development in the hippocampus as well as deficits in cognition and increased depressive-like symptoms. Leptin increases glutamatergic synaptogenesis, in part, through enhancement of N-methyl-D-aspartic acid (NMDA) receptor function; yet the underlying signaling pathway is not known. In this study, we examine how leptin regulates surface expression of NR2B-containing NMDA receptors in hippocampal neurons. Leptin stimulation increases NR2BY1472 phosphorylation, which is inhibited by the Src family kinase inhibitor, PP1. Moreover, we show that Fyn, a member of the Src family kinases, is required for leptin-stimulated NR2BY1472 phosphorylation. Furthermore, inhibiting Y1472 phosphorylation with either a dominant negative Fyn mutant or an NR2B mutant that lacks the phosphorylation site (NR2BY1472F) blocks leptin-stimulated synaptogenesis. Additionally, we show that LepRb forms a complex with NR2B and Fyn. Taken together, these findings expand our knowledge of the LepRb interactome and the mechanisms by which leptin stimulates glutamatergic synaptogenesis in the developing hippocampus. Comprehending these mechanisms is key for understanding dendritic spine development and synaptogenesis, alterations of which are associated with many neurological disorders.

Ketamine Regulates Phosphorylation of CRMP2 To Mediate Dendritic Spine Plasticity.

Ketamine is widely used in infants and young children for anesthesia, and subanesthetic doses of ketamine make neurons form new protrusions and promote synapse formation. However, the precise pathological mechanisms remain to be elucidated. In this study, we demonstrated that ketamine administration significantly increased dendritic spine density and maturity in rat cortical neurons in vivo and in vitro. Western blot analysis showed that CRMP2 protein expression was significantly increased in cerebral cortex of ketamine group, and phosphorylation levels of CRMP at Thr514 and Ser522 were significantly reduced. Furthermore, overexpression of CRMP2 promoted the growth of cortical neuron processes and dendritic spines. Although the dendritic field was more complex after adding ketamine and the density of dendritic spines increased, there was no statistical difference and no obvious superposition effect was observed. Moreover, both Ser522 mutant construction of CRMP2, GFP-CRMP2-522D, and mcherry-CDK5 showed similar inhibitory effects on neurite outgrowth, which could be rescued by ketamine. The frequency and amplitude of miniature excitatory postsynaptic currents (mEPSCs) were significantly inhibited when GFP-CRMP2-522D and mCherry-CDK5 were transfected into cortical neurons and this trend could also be rescued by ketamine. In general, this study reveals a new mechanism by which ketamine promotes the growth and development of dendritic spines in developing cortical neurons.

Usp9X Controls Ankyrin-Repeat Domain Protein Homeostasis during Dendritic Spine Development

Variants in the ANK3 gene encoding ankyrin-G areassociated with neurodevelopmental disorders, including intellectual disability, autism, schizophrenia, and bipolar disorder. However, no upstream regulators of ankyrin-G at synapses are known. Here, weshow that ankyrin-G interacts with Usp9X, a neurodevelopmental-disorder-associated deubiquitinase (DUB). Usp9X phosphorylation enhances their interaction, decreases ankyrin-G polyubiquitination, and stabilizes ankyrin-G to maintain dendritic spine development. In forebrain-specific Usp9X knockout mice (Usp9X-/Y), ankyrin-G as well as multiple ankyrin-repeat domain (ANKRD)-containing proteins are transiently reduced at 2 but recovered at 12weeks postnatally. However, reduced cortical spine density in knockouts persists into adulthood. Usp9X-/Y mice display increase of ankyrin-G ubiquitination and aggregation and hyperactivity. USP9X mutations in patients with intellectual disability and autism ablate its catalytic activity or ankyrin-G interaction. Our data reveal a DUB-dependent mechanism of ANKRD protein homeostasis, the impairment of which only transientlyaffects ANKRD protein levels but leads topersistent neuronal, behavioral, and clinical abnormalities.

Lanthanum Chloride Impairs Learning and Memory and Induces Dendritic Spine Abnormality by Down-Regulating Rac1/PAK Signaling Pathway in Hippocampus of Offspring Rats.

Lanthanum (La) is a natural rare earth element. It has neurotoxic effects which can impair learning and memory in humans. However, its mechanism of neurotoxicity is unclear. Learning and memory are coordinated by dendritic spines which form tiny protruding structures on the dendritic branches of neurons. This study investigated the effect of LaCl3 exposure to pregnant and lactating rats on the offspring rats' learning and memory ability. In this study, rats were divided into 4 groups and given distilled water solution containing 0%, 0.125%, 0.25%, 0.5% LaCl3, respectively, and this was done from conception to the end of the location. The effects of LaCl3 on spatial learning and memory ability in offspring rats and in the development of dendritic spines in CA1 pyramidal cells were investigated. The results showed that LaCl3 impaired spatial learning and memory ability in offspring rats, and decreased dendritic spine density during development. In addition, LaCl3 can affect the expression of CaMKII, miRNA132, p250GAP, Tiam1, PARD3, and down-regulated the activation of Rac1 which led to a decrease in the expression of Rac1/PAK signaling pathway and downstream regulatory proteins Cortactin and actin-related protein 2/3 complex (Arp2/3 complex). This study indicated that the learning and memory impairment and the decrease of dendritic spine density in the offspring of LaCl3 exposure may be related to the down-regulation of the Rac1/PAK signaling pathway regulated by Tiam1 and p250GAP.

Role of brain-specific angiogenesis inhibitor 1 in synapse and cognitive impairment

Adhesion G protein-coupled receptors(aGPCRs) play a significant role in cognitive impairment related diseases. As an important member of aGPCRs, brain-specific angiogenesis inhibitor 1(BAI1) has a prominent impact on anti-angiogenesis, anti-tumor and participating in immune phagocytosis. Recent research found out that BAI1 exerts a great influence on synaptogenesis and synaptic plasticity, but few studying concerning BAI1 in nervous system. Nowadays, the aging of population aggravates the occurrence of cognitive impairment. The pathogenesis of Alzheimer's disease and vascular cognitive impairment remains elusive, and identification of cognitive impairment at an early stage faces challenges. In the stage of mild cognitive impairment, synaptic damage is evident. BAI1 can regulate the function of postsynaptic membrane, synaptogenesis, synaptic signal transmission and the morphological development of dendritic spines. Therefore, it may potentially act as an early-warning index and intervention target for cognitive impairment. Key words: Brain-specific angiogenesis inhibitor 1; Cognitive impairment; Adhesion G protein-coupled receptors; Synaptogenesis; Mild cognitive impairment

Autism candidate gene DIP2A regulates spine morphogenesis via acetylation of cortactin.

Dendritic spine development is crucial for the establishment of excitatory synaptic connectivity and functional neural circuits. Alterations in spine morphology and density have been associated with multiple neurological disorders. Autism candidate gene disconnected-interacting protein homolog 2 A (DIP2A) is known to be involved in acetylated coenzyme A (Ac-CoA) synthesis and is primarily expressed in the brain regions with abundant pyramidal neurons. However, the role of DIP2A in the brain remains largely unknown. In this study, we found that deletion of Dip2a in mice induced defects in spine morphogenesis along with thin postsynaptic density (PSD), and reduced synaptic transmission of pyramidal neurons. We further identified that DIP2A interacted with cortactin, an activity-dependent spine remodeling protein. The binding activity of DIP2A-PXXP motifs (P, proline; X, any residue) with the cortactin-Src homology 3 (SH3) domain was critical for maintaining the level of acetylated cortactin. Furthermore, Dip2a knockout (KO) mice exhibited autism-like behaviors, including excessive repetitive behaviors and defects in social novelty. Importantly, acetylation mimetic cortactin restored the impaired synaptic transmission and ameliorated repetitive behaviors in these mice. Altogether, our findings establish an initial link between DIP2A gene variations in autism spectrum disorder (ASD) and highlight the contribution of synaptic protein acetylation to synaptic processing.

Neuropilin 2 Signaling Mediates Corticostriatal Transmission, Spine Maintenance, and Goal-Directed Learning in Mice.

The striatum represents the main input structure of the basal ganglia, receiving massive excitatory input from the cortex and the thalamus. The development and maintenance of cortical input to the striatum is crucial for all striatal function including many forms of sensorimotor integration, learning, and action control. The molecular mechanisms regulating the development and maintenance of corticostriatal synaptic transmission are unclear. Here we show that the guidance cue, Semaphorin 3F and its receptor Neuropilin 2 (Nrp2), influence dendritic spine maintenance, corticostriatal short-term plasticity, and learning in adult male and female mice. We found that Nrp2 is enriched in adult layer V pyramidal neurons, corticostriatal terminals, and in developing and adult striatal spiny projection neurons (SPNs). Loss of Nrp2 increases SPN excitability and spine number, reduces short-term facilitation at corticostriatal synapses, and impairs goal-directed learning in an instrumental task. Acute deletion of Nrp2 selectively in adult layer V cortical neurons produces a similar increase in the number of dendritic spines and presynaptic modifications at the corticostriatal synapse in the Nrp2-/- mouse, but does not affect the intrinsic excitability of SPNs. Furthermore, conditional loss of Nrp2 impairs sensorimotor learning on the accelerating rotarod without affecting goal-directed instrumental learning. Collectively, our results identify Nrp2 signaling as essential for the development and maintenance of the corticostriatal pathway and may shed novel insights on neurodevelopmental disorders linked to the corticostriatal pathway and Semaphorin signaling.SIGNIFICANCE STATEMENT The corticostriatal pathway controls sensorimotor, learning, and action control behaviors and its dysregulation is linked to neurodevelopmental disorders, such as autism spectrum disorder (ASD). Here we demonstrate that Neuropilin 2 (Nrp2), a receptor for the axon guidance cue semaphorin 3F, has important and previously unappreciated functions in the development and adult maintenance of dendritic spines on striatal spiny projection neurons (SPNs), corticostriatal short-term plasticity, intrinsic physiological properties of SPNs, and learning in mice. Our findings, coupled with the association of Nrp2 with ASD in human populations, suggest that Nrp2 may play an important role in ASD pathophysiology. Overall, our work demonstrates Nrp2 to be a key regulator of corticostriatal development, maintenance, and function, and may lead to better understanding of neurodevelopmental disease mechanisms.

Dendritic cell factor 1 deletion leads to developmental defects in mushroom-shaped dendritic spines.

Dendritic spines are divided into four subtypes, namely, Mushroom, Stubby, Thin, and Branched. The mushroom-shaped spines are related to learning and memory. Previous studies have shown that the dendritic cell factor 1 (Dcf1, a transmembrane protein) affects the memory process and regulates the development of dendritic spines by inhibiting the expression of lipocalin 2 (Lcn2, a member of the family containing over 20 small secreted proteins). However, the exact subtype of dendritic spines that are specifically affected by Dcf1 remains unknown. Here, we identified that deletion of Dcf1 leads to developmental defects in mushroom-shaped spines. We provide evidence for memory defects caused by Dcf1-knockout in mice. We discovered and report for the first time that Dcf1 affects the development of mushroom-shaped spines by inhibiting the expression of Lcn2. Further, we demonstrated that environmental enrichment can effectively stimulate Dcf1-knockout mice and rescue development defects in mushroom-shaped spines caused by Dcf1 deletion. Our results provide a novel direction for further studies on dendritic spine development and mechanisms associated with learning and memory.

PLD1 promotes dendritic spine morphogenesis via activating PKD1

Dendritic spines on the dendrites of pyramidal neurons are one of the most important components for excitatory synapses, where excitatory information exchanges and integrates. The defects of dendritic spine development have been closely connected with many nervous system diseases including autism, intellectual disability and so forth. Based on our previous studies, we here report a new functional signaling link between phospholipase D1 (PLD1) and protein kinase D1 (PKD1) in dendritic spine morphogenesis. Coimmunoprecipitation assays showed that PLD1 associates with PKD1. A series of knocking down and rescuing experiments demonstrated that PLD1 acts upstream of PKD1 in positively regulating dendritic spine morphogenesis. Using PLD1 inhibitor, we found that PLD1 activates PKD1 to promote dendritic spine morphogenesis. Thus, we further reveal the roles of the two different enzymes in neuronal development.

Altered cortical Cytoarchitecture in the Fmr1 knockout mouse

Fragile X syndrome (FXS) is a neurodevelopmental disorder caused by silencing of the FMR1 gene and subsequent loss of its protein product, fragile X retardation protein (FMRP). One of the most robust neuropathological findings in post-mortem human FXS and Fmr1 KO mice is the abnormal increase in dendritic spine densities, with the majority of spines showing an elongated immature morphology. However, the exact mechanisms of how FMRP can regulate dendritic spine development are still unclear. Abnormal dendritic spines can result from disturbances of multiple factors during neurodevelopment, such as alterations in neuron numbers, position and glial cells. In this study, we undertook a comprehensive histological analysis of the cerebral cortex in Fmr1 KO mice. They displayed significantly fewer neuron and PV-interneuron numbers, along with altered cortical lamination patterns. In terms of glial cells, Fmr1 KO mice exhibited an increase in Olig2-oligodendrocytes, which corresponded to the abnormally higher myelin expression in the corpus callosum. Iba1-microglia were significantly reduced but GFAP-astrocyte numbers and intensity were elevated. Using primary astrocytes derived from KO mice, we further demonstrated the presence of astrogliosis characterized by an increase in GFAP expression and astrocyte hypertrophy. Our findings provide important information on the cortical architecture of Fmr1 KO mice, and insights towards possible mechanisms associated with FXS.

Neonatal treatment with cyclosporine A restores neurogenesis and spinogenesis in the Ts65Dn model of Down syndrome

Down syndrome (DS), a genetic condition due to triplication of chromosome 21, is characterized by reduced proliferation of neural progenitor cells (NPCs) starting from early life stages. This defect is worsened by a reduction of neuronogenesis (accompanied by an increase in astrogliogenesis) and dendritic spine atrophy. Since this triad of defects underlies intellectual disability, it seems important to establish whether it is possible to pharmacologically correct these alterations. In this study, we exploited the Ts65Dn mouse model of DS in order to obtain an answer to this question. In the framework of an in vitro drug-screening campaign of FDA/EMA-approved drugs, we found that the immunosuppressant cyclosporine A (CSA) restored proliferation, acquisition of a neuronal phenotype, and maturation of neural progenitor cells (NPCs) from the subventricular zone (SVZ) of the lateral ventricle of Ts65Dn mice. Based on these findings, we treated Ts65Dn mice with CSA in the postnatal period P3-P15. We found that treatment fully restored NPC proliferation in the SVZ and in the subgranular zone of the hippocampal dentate gyrus, and total number of hippocampal granule cells. Moreover, CSA enhanced development of dendritic spines on the dendritic arbor of the granule cells whose density even surpassed that of euploid mice. In hippocampal homogenates from Ts65Dn mice, we found that CSA normalized the excessive levels of p21, a key determinant of proliferation impairment. Results show that neonatal treatment with CSA restores the whole triad of defects of the trisomic brain. In DS CSA treatment may pose caveats because it is an immunosuppressant that may cause adverse effects. However, CSA analogues that mimic its effect without eliciting immunosuppression may represent practicable tools for ameliorating brain development in individuals with DS.

Rare inherited missense variants of POGZ associate with autism risk and disrupt neuronal development

Excess de novo likely gene-disruptive and missense variants within dozens of genes have been identified in autism spectrum disorder (ASD) and other neurodevelopmental disorders. However, many rare inherited missense variants of these high-risk genes have not been thoroughly evaluated. In this study, we analyzed the rare missense variant burden of POGZ in a large cohort of ASD patients from the Autism Clinical and Genetic Resources in China (ACGC) and further dissected the functional effect of disease-associated missense variants on neuronal development. Our results showed a significant burden of rare missense variants in ASD patients compared to the control population (P = 4.6 × 10−5, OR = 3.96), and missense variants in ASD patients showed more severe predicted functional outcomes than those in controls. Furthermore, by leveraging published large-scale sequencing data of neurodevelopmental disorders (NDDs) and sporadic case reports, we identified 8 de novo missense variants of POGZ in NDD patients. Functional analysis revealed that two inherited, but not de novo, missense variants influenced the cellular localization of POGZ and failed to rescue the defects in neurite and dendritic spine development caused by Pogz knockdown in cultured mouse primary cortical neurons. Significantly, L1CAM, an autism candidate risk gene, is differentially expressed in POGZ deficient cell lines. Reduced expression of L1cam was able to partially rescue the neurite length defects caused by Pogz knockdown. Our study showed the important roles of rare inherited missense variants of POGZ in ASD risk and neuronal development and identified the potential downstream targets of POGZ, which are important for further molecular mechanism studies.

Pannexin 1 Regulates Network Ensembles and Dendritic Spine Development in Cortical Neurons.

Dendritic spines are the postsynaptic targets of excitatory synaptic inputs that undergo extensive proliferation and maturation during the first postnatal month in mice. However, our understanding of the molecular mechanisms that regulate spines during this critical period is limited. Previous work has shown that pannexin 1 (Panx1) regulates neurite growth and synaptic plasticity. We therefore investigated the impact of global Panx1 KO on spontaneous cortical neuron activity using Ca2+ imaging and in silico network analysis. Panx1 KO increased both the number and size of spontaneous co-active cortical neuron network ensembles. To understand the basis for these findings, we investigated Panx1 expression in postnatal synaptosome preparations from early postnatal mouse cortex. Between 2 and 4 postnatal weeks, we observed a precipitous drop in cortical synaptosome protein levels of Panx1, suggesting it regulates synapse proliferation and/or maturation. At the same time points, we observed significant enrichment of the excitatory postsynaptic density proteins PSD-95, GluA1, and GluN2a in cortical synaptosomes from global Panx1 knock-out mice. Ex vivo analysis of pyramidal neuron structure in somatosensory cortex revealed a consistent increase in dendritic spine densities in both male and female Panx1 KO mice. Similar findings were observed in an excitatory neuron-specific Panx1 KO line (Emx1-Cre driven; Panx1 cKOE) and in primary Panx1 KO cortical neurons cultured in vitro. Altogether, our study suggests that Panx1 negatively regulates cortical dendritic spine development.

An autism-linked missense mutation in SHANK3 reveals the modularity of Shank3 function.

Genome sequencing has revealed an increasing number of genetic variations that are associated with neuropsychiatric disorders. Frequently, studies limit their focus to likely gene-disrupting mutations because they are relatively easy to interpret. Missense variants, instead, have often been undervalued. However, some missense variants can be informative for developing a more profound understanding of disease pathogenesis and ultimately targeted therapies. Here we present an example of this by studying a missense variant in a well-known autism spectrum disorder (ASD) causing gene SHANK3. We analyzed Shank3’s in vivo phosphorylation profile and identified S685 as one phosphorylation site where one ASD-linked variant has been reported. Detailed analysis of this variant revealed a novel function of Shank3 in recruiting Abelson interactor 1 (ABI1) and the WAVE complex to the post-synaptic density (PSD), which is critical for synapse and dendritic spine development. This function was found to be independent of Shank3’s other functions such as binding to GKAP and Homer. Introduction of this human ASD mutation into mice resulted in a small subset of phenotypes seen previously in constitutive Shank3 knockout mice, including increased allogrooming, increased social dominance, and reduced pup USV. Together, these findings demonstrate the modularity of Shank3 function in vivo. This modularity further indicates that there is more than one independent pathogenic pathway downstream of Shank3 and correcting a single downstream pathway is unlikely to be sufficient for clear clinical improvement. In addition, this study illustrates the value of deep biological analysis of select missense mutations in elucidating the pathogenesis of neuropsychiatric phenotypes.

Sh3rf2 Haploinsufficiency Leads to Unilateral Neuronal Development Deficits and Autistic-Like Behaviors in Mice

Autism spectrum disorders (ASDs) include a variety of developmental brain disorders with clinical findings implicating the dysfunction of the left hemisphere. Here, we generate mice lacking one copy of Sh3rf2, which was detected in ASD patients, to determine whether Sh3rf2 is involved in brain development and whether mutation of SH3RF2 is causative for ASD and the mechanisms linking it to ASD traits. We find that mice with Sh3rf2 haploinsufficiency display significant deficits in social interactionand communication, as well as stereotyped orrepetitive behaviors and hyperactivity and seizures. Disturbances in hippocampal dendritic spine development, aberrant composition of glutamatergic receptor subunits, and abnormal excitatory synaptictransmission were detected in heterozygous mutants. Remarkably, these defects are selectively unilateral. Our results support a notion that Sh3rf2 haploinsufficiency is a highly penetrant risk factor for ASD, with disease pathogenesis most likely resulting from deficits in synaptic function in the left hemisphere of the brain.

Disruption of MET Receptor Tyrosine Kinase, an Autism Risk Factor, Impairs Developmental Synaptic Plasticity in the Hippocampus.

As more genes conferring risks to neurodevelopmental disorders are identified, translating these genetic risk factors into biological mechanisms that impact the trajectory of the developing brain is a critical next step. Here, we report that disrupted signaling mediated MET receptor tyrosine kinase (RTK), an established risk factor for autism spectrum disorders, in the developing hippocampus glutamatergic circuit leads to profound deficits in neural development, synaptic transmission, and plasticity. In cultured hippocampus slices prepared from neonatal mice, pharmacological inhibition of MET kinase activity suppresses dendritic arborization and disrupts normal dendritic spine development. In addition, single-neuron knockdown (RNAi) or overexpression of Met in the developing hippocampal CA1 neurons leads to alterations, opposite in nature, in basal synaptic transmission and long-term plasticity. In forebrain-specific Met conditional knockout mice (Metfx/fx ;emx1cre ), an enhanced long-term potentiation (LTP) and long-term depression (LTD) were observed at early developmental stages (P12-14) at the Schaffer collateral to CA1 synapses compared with wild-type littermates. In contrast, LTP and LTD were markedly reduced at young adult stage (P56-70) during which wild-type mice show robust LTP and LTD. The altered trajectory of synaptic plasticity revealed by this study indicate that temporally regulated MET signaling as an intrinsic, cell autonomous, and pleiotropic mechanism not only critical for neuronal growth and functional maturation, but also for the timing of synaptic plasticity during forebrain glutamatergic circuits development.

Neurocan Inhibits Semaphorin 3F Induced Dendritic Spine Remodeling Through NrCAM in Cortical Neurons.

Neurocan is a chondroitin sulfate proteoglycan present in perineuronal nets, which are associated with closure of the critical period of synaptic plasticity. During postnatal development of the neocortex dendritic spines on pyramidal neurons are initially overproduced; later they are pruned to achieve an appropriate balance of excitatory to inhibitory synapses. Little is understood about how spine pruning is terminated upon maturation. NrCAM (Neuron-glial related cell adhesion molecule) was found to mediate spine pruning as a subunit of the receptor complex for the repellent ligand Semaphorin 3F (Sema3F). As shown here in the postnatal mouse frontal and visual neocortex, Neurocan was localized at both light and electron microscopic level to the cell surface of cortical pyramidal neurons and was adjacent to neuronal processes and dendritic spines. Sema3F-induced spine elimination was inhibited by Neurocan in cortical neuron cultures. Neurocan also blocked Sema3F-induced morphological retraction in COS-7 cells, which was mediated through NrCAM and other subunits of the Sema3F holoreceptor, Neuropilin-2, and PlexinA3. Cell binding and ELISA assays demonstrated an association of Neurocan with NrCAM. Glycosaminoglycan chain interactions of Neurocan were required for inhibition of Sema3F-induced spine elimination, but the C-terminal sushi domain was dispensable. These results describe a novel mechanism wherein Neurocan inhibits NrCAM/Sema3F-induced spine elimination.