Complementary expression and heterophilic interactions between IgLON family members neurotrimin and LAMP

IgLON5 deficiency produces behavioral alterations in a knockout mouse model

Background

Anti-IgLON5 disease is a neurological disorder characterized by autoantibodies against IgLON5 and pathological evidence of neurodegeneration. IgLON5 is a cell adhesion molecule of unknown function that is highly expressed in the brain. Our aim was to investigate the impact of IgLON5 loss-of-function in evaluating brain morphology, social behavior, and the development of symptoms observed in an IgLON5 knockout (IgLON5-KO) mouse model.

Methods

The IgLON5-KO mice were generated using CRISPR-Cas9 technology. Immunohistochemistry on fixed sagittal brain sections and Western blotting brain lysates were used to confirm IgLON5 silencing and to evaluate the presence of other cell surface proteins. Two- month-old IgLON5-KO and wild-type (WT) mice underwent a comprehensive battery of behavioral tests to assess 1) locomotion, 2) memory, 3) anxiety, 4) social interaction, and 5) depressive-like behavior. Brain sections were examined for the presence of anatomical abnormalities and deposits of hyperphosphorylated tau in young adult (2-month-old) and aged (22-month-old) mice.

Results

Mice did not develop neurological symptoms reminiscent of those seen in patients with anti-IgLON5 disease. Behavioral testing revealed that 2-month-old IgLON5-KO mice showed subtle alterations in motor coordination and balance. IgLON5-KO females exhibited hyperactivity during night and day. Males were observed to have depressive-like behavior and excessive nest-building behavior. Neuropathological studies did not reveal brain morphological alterations or hyperphosphorylated tau deposits.

Conclusion

IgLON5-KO mice showed subtle alterations in behavior and deficits in fine motor coordination but did not develop the clinical phenotype of anti-IgLON5 disease.

The Role of IgLON Cell Adhesion Molecules in Neurodegenerative Diseases

In the brain, cell adhesion molecules (CAMs) are critical for neurite outgrowth, axonal fasciculation, neuronal survival and migration, and synapse formation and maintenance. Among CAMs, the IgLON family comprises five members: Opioid Binding Protein/Cell Adhesion Molecule Like (OPCML or OBCAM), Limbic System Associated Membrane Protein (LSAMP), neurotrimin (NTM), Neuronal Growth Regulator 1 (NEGR1), and IgLON5. IgLONs exhibit three N-terminal C2 immunoglobulin domains; several glycosylation sites; and a glycosylphosphatidylinositol anchoring to the membrane. Interactions as homo- or heterodimers in cis and in trans, as well as binding to other molecules, appear critical for their functions. Shedding by metalloproteases generates soluble factors interacting with cellular receptors and activating signal transduction. The aim of this review was to analyse the available data implicating a role for IgLONs in neuropsychiatric disorders. Starting from the identification of a pathological role for antibodies against IgLON5 in an autoimmune neurodegenerative disease with a poorly understood mechanism of action, accumulating evidence links IgLONs to neuropsychiatric disorders, albeit with still undefined mechanisms which will require future thorough investigations.

Patients' IgLON5 autoantibodies interfere with IgLON5-protein interactions

Background

Anti-IgLON5 disease is a rare neurological disorder characterized by autoantibodies against IgLON5, and pathological evidence of neurodegeneration. IgLON5 is a cell adhesion molecule but its physiological function is unknown. Our aim was to investigate the IgLON5 interactome and to determine if IgLON5 antibodies (IgLON5-abs) affect these protein interactions.

Methods

IgLON5 interactome was investigated by mass spectrometry sequencing of proteins immunoprecipitated by IgLON5 autoantibodies using cultures of rat cerebellar granular neurons (CGNs). Shedding of IgLON5 was explored using HEK cells transfected with human IgLON5 plasmid and in CGNs. Interactions of IgLON5 with identified binding partners and IgLON5-abs effects were confirmed by immunofluorescence in transfected HEK cells and rat hippocampal neurons.

Results

Patients' IgLON5 antibodies co-precipitated all members of the IgLON family and three 3 additional surface proteins. IgLON5 predominantly establishes homomeric and heteromeric cis (within the cell) and trans (between cells)-interactions with other IgLON family members and undergoes spontaneous ectodomain shedding. Antibodies from patients with anti-IgLON5 disease prevent trans-interactions in hippocampal neurons independently of the IgLON5 IgG subclass distribution.

Conclusions

We show a potentially novel pathogenic mechanism of IgLON5-abs that consists in blocking IgLON5 interactions with its binding partners. These findings extend our knowledge about the physiological role of IgLON5 and pave the way to future understanding of the pathological mechanisms of anti-IgLON5 disease.

Differential Expression of MED12-Associated Coding RNA Transcripts in Uterine Leiomyomas

Recent studies have demonstrated that somatic MED12 mutations in exon 2 occur at a frequency of up to 80% and have a functional role in leiomyoma pathogenesis. The objective of this study was to elucidate the expression profile of coding RNA transcripts in leiomyomas, with and without these mutations, and their paired myometrium. Next-generation RNA sequencing (NGS) was used to systematically profile the differentially expressed RNA transcripts from paired leiomyomas (n = 19). The differential analysis indicated there are 394 genes differentially and aberrantly expressed only in the mutated tumors. These genes were predominantly involved in the regulation of extracellular constituents. Of the differentially expressed genes that overlapped in the two comparison groups, the magnitude of change in gene expression was greater for many genes in tumors bearing MED12 mutations. Although the myometrium did not express MED12 mutations, there were marked differences in the transcriptome landscape of the myometrium from mutated and non-mutated specimens, with genes regulating the response to oxygen-containing compounds being most altered. In conclusion, MED12 mutations have profound effects on the expression of genes pivotal to leiomyoma pathogenesis in the tumor and the myometrium which could alter tumor characteristics and growth potential.

How "Neuronal" Are Human Skin Mast Cells?

Mast cells are evolutionarily old cells and the principal effectors in allergic responses and inflammation. They are seeded from the yolk sac during embryogenesis or are derived from hematopoietic progenitors and are therefore related to other leukocyte subsets, even though they form a separate clade in the hematopoietic system. Herein, we systematically bundle information from several recent high-throughput endeavors, especially those comparing MCs with other cell types, and combine such information with knowledge on the genes’ functions to reveal groups of neuronal markers specifically expressed by MCs. We focus on recent advances made regarding human tissue MCs, but also refer to studies in mice. In broad terms, genes hyper-expressed in MCs, but largely inactive in other myelocytes, can be classified into subcategories such as traffic/lysosomes (MLPH and RAB27B), the dopamine system (MAOB, DRD2, SLC6A3, and SLC18A2), Ca²⁺-related entities (CALB2), adhesion molecules (L1CAM and NTM) and, as an overall principle, the transcription factors and modulators of transcriptional activity (LMO4, PBX1, MEIS2, and EHMT2). Their function in MCs is generally unknown but may tentatively be deduced by comparison with other systems. MCs share functions with the nervous system, as they express typical neurotransmitters (histamine and serotonin) and a degranulation machinery that shares features with the neuronal apparatus at the synapse. Therefore, selective overlaps are plausible, and they further highlight the uniqueness of MCs within the myeloid system, as well as when compared with basophils. Apart from investigating their functional implications in MCs, a key question is whether their expression in the lineage is due to the specific reactivation of genes normally silenced in leukocytes or whether the genes are not switched off during mastocytic development from early progenitors.

Spatiotemporal expression of IgLON family members in the developing mouse nervous system

Differential expression of cell adhesion molecules in neuronal populations is one of the many mechanisms promoting the formation of functional neural circuits in the developing nervous system. The IgLON family consists of five cell surface immunoglobulin proteins that have been associated with various developmental disorders, such as autism spectrum disorder, schizophrenia, and major depressive disorder. However, there is still limited and fragmented information about their patterns of expression in certain regions of the developing nervous system and how their expression contributes to their function. Utilizing an in situ hybridization approach, we have analyzed the spatiotemporal expression of all IgLON family members in the developing mouse brain, spinal cord, eye, olfactory epithelium, and vomeronasal organ. At one prenatal (E16) and two postnatal (P0 and P15) ages, we show that each IgLON displays distinct expression patterns in the olfactory system, cerebral cortex, midbrain, cerebellum, spinal cord, and eye, indicating that they likely contribute to the wiring of specific neuronal circuitry. These analyses will inform future functional studies aimed at identifying additional roles for these proteins in nervous system development.

Alternative Promoter Use Governs the Expression of IgLON Cell Adhesion Molecules in Histogenetic Fields of the Embryonic Mouse Brain

The members of the IgLON superfamily of cell adhesion molecules facilitate fundamental cellular communication during brain development, maintain functional brain circuitry, and are associated with several neuropsychiatric disorders such as depression, autism, schizophrenia, and intellectual disabilities. Usage of alternative promoter-specific 1a and 1b mRNA isoforms in Lsamp, Opcml, Ntm, and the single promoter of Negr1 in the mouse and human brain has been previously described. To determine the precise spatiotemporal expression dynamics of Lsamp, Opcml, Ntm isoforms, and Negr1, in the developing brain, we generated isoform-specific RNA probes and carried out in situ hybridization in the developing (embryonic, E10.5, E11.5, 13.5, 17; postnatal, P0) and adult mouse brains. We show that promoter-specific expression of IgLONs is established early during pallial development (at E10.5), where it remains throughout its differentiation through adulthood. In the diencephalon, midbrain, and hindbrain, strong expression patterns are initiated a few days later and begin fading after birth, being only faintly expressed during adulthood. Thus, the expression of specific IgLONs in the developing brain may provide the means for regionally specific functionality as well as for specific regional vulnerabilities. The current study will therefore improve the understanding of how IgLON genes are implicated in the development of neuropsychiatric disorders.

Highly Conserved Molecular Features in IgLONs Contrast Their Distinct Structural and Biological Outcomes

Neuronal growth regulator 1 (NEGR1) and neurotrimin (NTM) are abundant cell-surface proteins found in the brain and form part of the IgLON (Immunoglobulin LSAMP, OBCAM, Neurotrimin) family. In humans, NEGR1 is implicated in obesity and mental disorders, while NTM is linked to intelligence and cognitive function. IgLONs dimerize homophilically and heterophilically, and they are thought to shape synaptic connections and neural circuits by acting in trans (spanning cellular junctions) and/or in cis (at the same side of a junction). Here, we reveal homodimeric structures of NEGR1 and NTM. They assemble into V-shaped complexes via their Ig1 domains, and disruption of the Ig1-Ig1 interface abolishes dimerization in solution. A hydrophobic ridge from one Ig1 domain inserts into a hydrophobic pocket from the opposing Ig1 domain producing an interaction interface that is highly conserved among IgLONs but remarkably plastic structurally. Given the high degree of sequence conservation at the interaction interface, we tested whether different IgLONs could elicit the same biological effect in vivo. In a small-scale study administering different soluble IgLONs directly into the brain and monitoring feeding, only NEGR1 altered food intake significantly. Taking NEGR1 as a prototype, our studies thus indicate that while IgLONs share a conserved mode of interaction and are able to bind each other as homomers and heteromers, they are structurally plastic and can exert unique biological action.

Expression and impact of Lsamp neural adhesion molecule in the serotonergic neurotransmission system

Limbic system associated membrane protein (Lsamp) is a neural adhesion protein which has been recently found to be differentially expressed between serotonergic neuron subtypes. We have previously shown elevated serotonin (5-HT) turnover rate in Lsamp-deficient mice. The purpose of the current study was to elucidate the role of Lsamp in serotonergic neurotransmission. Chronic (18 days) administration of serotonin reuptake inhibitor (SSRI) escitalopram (10 mg/kg) significantly increased general activity in wild-type mice in the open field and protected exploration in Lsamp^-/- mice in the elevated-plus maze. An important psychopathology-related endophenotype, elevated 5-HT turnover in the brain of Lsamp-deficient mice, was reproduced in the saline group. Escitalopram restored the elevated 5-HT turnover of Lsamp-deficient mice to a level comparable with their wild-type littermates, suggesting that high 5-HT turnover in mutants is mediated by the increased activity of serotonin transporter (SERT protein encoded by Slc6a4 gene). The baseline level of Slc6a4 transcript was not changed in Lsamp-deficient mice, however, our immunohistochemical analysis showed partial co-expression of Lsamp with both SERT and Tph2 proteins in raphe. Overactivity of SERT in Lsamp^-/- mice is further supported by significant elevation of Maoa transcript and increase of DOPAC, another Mao A product, specifically in the raphe. Again, elevation of DOPAC was reduced to the level of wild-type by chronic SSRI treatment. The activity of Lsamp gene promoters varied in 5-HT producing nuclei: both Lsamp 1a and 1b promoters were active in the dorsal raphe; most of the expression in the median raphe was from 1b promoter, whereas Lsamp 1a promoter was almost exclusively active in the caudal subgroup of raphe nuclei. We suggest that Lsamp may have an impact on the integrity of serotonergic synapses, which is possibly the neurochemical basis of the anxiety- and sociability-related phenotype in Lsamp-deficient mice.

Steroid hormones and hormone antagonists regulate the neural marker neurotrimin in uterine leiomyoma

OBJECTIVE

To characterize the role of steroid hormone and antihormone exposure on neurotrimin (NTM) expression in human leiomyoma and myometrial tissue and cells.

DESIGN

Laboratory study of placebo and ulipristal acetate (UPA)-treated patient tissue. In vitro assessment of immortalized myometrial and leiomyoma cell lines after hormone and antihormone exposure.

SETTING

Academic research center.

PATIENT(S)

Not applicable.

INTERVENTIONS(S)

Exposure of leiomyoma cell lines to 17β-E₂, medroxyprogesterone acetate (MPA), UPA, and fulvestrant.

MAIN OUTCOME MEASURE(S)

Messenger RNA expression quantified with the use of RNASeq analysis and quantitative real-time polymerase chain reaction (qRT-PCR). Protein levels quantified by means of Western blot analysis. Immunohistochemistry (IHC) on placebo- and UPA-treated patient uterine tissue specimens.

RESULT(S)

Expression of NTM in human uterine leiomyoma specimens according to RNASeq was increased compared with myometrium (5.22 ± 0.57-fold), which was confirmed with the use of qRT-PCR (1.95 ± 0.05). Furthermore, NTM protein was elevated in leiomyoma tissue compared with matched myometrium (2.799 ± 0.575). IHC revealed increased staining intensity in leiomyoma surgical specimens compared with matched myometrium of placebo patients. Western blot analysis in immortalized leiomyoma cell lines demonstrated an up-regulation of NTM protein expression (2.4 ± 0.04). Treatment of leiomyoma cell lines with 17β-E₂ yielded a 1.98 ± 0.11-fold increase in NTM protein expression; however, treatment with fulvestrant showed no significant change compared with control. Leiomyoma cell lines demonstrated a 1.91 ± 0.97-fold increase in NTM protein expression after progesterone treatment. RNASeq analysis demonstrated a reduced expression in patient leiomyoma after UPA treatment (0.75 ± 0.14). Treatment of leiomyoma cells with UPA demonstrated a reduced total NTM protein amount (0.54 ± 0.31) in patients, which was confirmed with the use of IHC (UPA10 147.2 ± 9.40, UPA20 182.8 ± 8.98). In vitro studies with UPA treatment revealed a concentration-dependent effect that supported these findings.

CONCLUSION(S)

NTM, a neural cell adhesion molecule, is increased in leiomyoma compared with myometrium in patient tissue and in vitro models after estrogen and progesterone treatment. Down-regulation of expression occurs after UPA treatment, but not after fulvestrant exposure.

CLINICAL TRIAL REGISTRATION NUMBER

NCT00290251.

Emerging roles for the GPI-anchored tumor suppressor OPCML in cancers

OPCML is a highly conserved glycosyl phosphatidylinositol (GPI)-anchored protein belonging to the IgLON family of cell adhesion molecules. OPCML functions as a tumor suppressor and is silenced in over 80% of ovarian cancers by loss of heterozygosity and by epigenetic mechanisms. OPCML inactivation is also observed in many other cancers suggesting a conservation of tumor suppressor function. Although epigenetic silencing and subsequent loss of OPCML expression correlate with poor progression-free and overall patient survival, its mechanism of action is only starting to be fully elucidated. Recent discoveries have demonstrated that OPCML exerts its tumor suppressor effect by inhibiting several cancer hallmark phenotypes in vitro and abrogating tumorigenesis in vivo, by downregulating/inactivating a specific spectrum of Receptor Tyrosine Kinases (RTKs), including EphA2, FGFR1, FGFR3, HER2, HER4, and AXL. This modulation of RTKs can also sensitize ovarian and breast cancers to lapatinib, erlotinib, and anti-AXL therapies. Furthermore, OPCML has also been shown to function in synergy with the tumor suppressor phosphatase PTPRG to inactivate pro-metastatic RTKs such as AXL. Recently, the identification of inactivating point mutations and the elucidation of the crystal structure of OPCML have provided valuable insights into its structure-function relationships, giving rise to its potential as an anti-cancer therapeutic.

Life-long epigenetic programming of cortical architecture by maternal 'Western' diet during pregnancy

The evolution of human diets led to preferences toward polyunsaturated fatty acid (PUFA) content with 'Western' diets enriched in ω-6 PUFAs. Mounting evidence points to ω-6 PUFA excess limiting metabolic and cognitive processes that define longevity in humans. When chosen during pregnancy, ω-6 PUFA-enriched 'Western' diets can reprogram maternal bodily metabolism with maternal nutrient supply precipitating the body-wide imprinting of molecular and cellular adaptations at the level of long-range intercellular signaling networks in the unborn fetus. Even though unfavorable neurological outcomes are amongst the most common complications of intrauterine ω-6 PUFA excess, cellular underpinnings of life-long modifications to brain architecture remain unknown. Here, we show that nutritional ω-6 PUFA-derived endocannabinoids desensitize CB₁ cannabinoid receptors, thus inducing epigenetic repression of transcriptional regulatory networks controlling neuronal differentiation. We found that cortical neurons lose their positional identity and axonal selectivity when mouse fetuses are exposed to excess ω-6 PUFAs in utero. Conversion of ω-6 PUFAs into endocannabinoids disrupted the temporal precision of signaling at neuronal CB₁ cannabinoid receptors, chiefly deregulating Stat3-dependent transcriptional cascades otherwise required to execute neuronal differentiation programs. Global proteomics identified the immunoglobulin family of cell adhesion molecules (IgCAMs) as direct substrates, with DNA methylation and chromatin accessibility profiling uncovering epigenetic reprogramming at >1400 sites in neurons after prolonged cannabinoid exposure. We found anxiety and depression-like behavioral traits to manifest in adult offspring, which is consistent with genetic models of reduced IgCAM expression, to suggest causality for cortical wiring defects. Overall, our data uncover a regulatory mechanism whose disruption by maternal food choices could limit an offspring's brain function for life.

NEGR1 and FGFR2 cooperatively regulate cortical development and core behaviours related to autism disorders in mice

Autism spectrum disorders are neurodevelopmental conditions with diverse aetiologies, all characterized by common core symptoms such as impaired social skills and communication, as well as repetitive behaviour. Cell adhesion molecules, receptor tyrosine kinases and associated downstream signalling have been strongly implicated in both neurodevelopment and autism spectrum disorders. We found that downregulation of the cell adhesion molecule NEGR1 or the receptor tyrosine kinase fibroblast growth factor receptor 2 (FGFR2) similarly affects neuronal migration and spine density during mouse cortical development in vivo and results in impaired core behaviours related to autism spectrum disorders. Mechanistically, NEGR1 physically interacts with FGFR2 and modulates FGFR2-dependent extracellular signal-regulated kinase (ERK) and protein kinase B (AKT) signalling by decreasing FGFR2 degradation from the plasma membrane. Accordingly, FGFR2 overexpression rescues all defects due to Negr1 knockdown in vivo. Negr1 knockout mice present phenotypes similar to Negr1-downregulated animals. These data indicate that NEGR1 and FGFR2 cooperatively regulate cortical development and suggest a role for defective NEGR1-FGFR2 complex and convergent downstream ERK and AKT signalling in autism spectrum disorders.

Increased sensitivity to psychostimulants and GABAergic drugs in Lsamp-deficient mice

Lsamp, in combinations with other members of the IgLON family of cell adhesion molecules, promotes and inhibits neurite outgrowth and synapse formation during development. Mice lacking Lsamp gene display decreased social behaviour, hyperactivity; decreased anxiety level, alongside with altered balance in GABAA receptor α1 and α2 subunits; and decreased sensitivity to amphetamine, alongside with elevated serotonin function. In human studies, Lsamp has been associated with several psychiatric diseases, including schizophrenia, and suicide. Here, we provide a more thorough characterization of the pharmacological phenotype of Lsamp-deficient mice, including testing for sensitivity to morphine, cocaine, MK-801 and ketamine. More thorougly, sensitivity to GABA modulators (diazepam, alprazolam, ethanol, pentobarbital, TP003, and SL651498) was assessed. In brief, Lsamp-deficient mice were more sensitive to the locomotor activating effects of cocaine and morphine, and hypersensitive to the sedative and muscle relaxant effects of GABA modulators, most likely reflecting enhanced function of α1 and α5 subunits of the GABAA receptor. No gross differences in sensitivity to NMDA receptor modulators were observed. Thus, as the lack of Lsamp gene leads to widespread imbalances in major neurotransmitter systems in the brain accompanied by remarkable changes in behavioural phenotype as well, Lsamp-deficient mice are a promising model for mimicking psychiatric disorders.

Family of neural wiring receptors in bilaterians defined by phylogenetic, biochemical, and structural evidence

The evolution of complex nervous systems was accompanied by the expansion of numerous protein families, including cell-adhesion molecules, surface receptors, and their ligands. These proteins mediate axonal guidance, synapse targeting, and other neuronal wiring-related functions. Recently, 32 interacting cell surface proteins belonging to two newly defined families of the Ig superfamily (IgSF) in fruit flies were discovered to label different subsets of neurons in the brain and ventral nerve cord. They have been shown to be involved in synaptic targeting and morphogenesis, retrograde signaling, and neuronal survival. Here, we show that these proteins, Dprs and DIPs, are members of a widely distributed family of two- and three-Ig domain molecules with neuronal wiring functions, which we refer to as Wirins. Beginning from a single ancestral Wirin gene in the last common ancestor of Bilateria, numerous gene duplications produced the heterophilic Dprs and DIPs in protostomes, along with two other subfamilies that diversified independently across protostome phyla. In deuterostomes, the ancestral Wirin evolved into the IgLON subfamily of neuronal receptors. We show that IgLONs interact with each other and that their complexes can be broken by mutations designed using homology models based on Dpr and DIP structures. The nematode orthologs ZIG-8 and RIG-5 also form heterophilic and homophilic complexes, and crystal structures reveal numerous apparently ancestral features shared with Dpr-DIP complexes. The evolutionary, biochemical, and structural relationships we demonstrate here provide insights into neural development and the rise of the metazoan nervous system.

A Proteomic Screen of Neuronal Cell-Surface Molecules Reveals IgLONs as Structurally Conserved Interaction Modules at the Synapse

In the developing brain, cell-surface proteins play crucial roles, but their protein-protein interaction network remains largely unknown. A proteomic screen identified 200 interactions, 89 of which were not previously published. Among these interactions, we find that the IgLONs, a family of five cell-surface neuronal proteins implicated in various human disorders, interact as homo- and heterodimers. We reveal their interaction patterns and report the dimeric crystal structures of Neurotrimin (NTRI), IgLON5, and the neuronal growth regulator 1 (NEGR1)/IgLON5 complex. We show that IgLONs maintain an extended conformation and that their dimerization occurs through the first Ig domain of each monomer and is Ca²⁺ independent. Cell aggregation shows that NTRI and NEGR1 homo- and heterodimerize in trans. Taken together, we report 89 unpublished cell-surface ligand-receptor pairs and describe structural models of trans interactions of IgLONs, showing that their structures are compatible with a model of interaction across the synaptic cleft.

Neural cell adhesion molecule Negr1 deficiency in mouse results in structural brain endophenotypes and behavioral deviations related to psychiatric disorders

Neuronal growth regulator 1 (NEGR1) belongs to the immunoglobulin (IgLON) superfamily of cell adhesion molecules involved in cortical layering. Recent functional and genomic studies implicate the role of NEGR1 in a wide spectrum of psychiatric disorders, such as major depression, schizophrenia and autism. Here, we investigated the impact of Negr1 deficiency on brain morphology, neuronal properties and social behavior of mice. In situ hybridization shows Negr1 expression in the brain nuclei which are central modulators of cortical-subcortical connectivity such as the island of Calleja and the reticular nucleus of thalamus. Brain morphological analysis revealed neuroanatomical abnormalities in Negr1^−/− mice, including enlargement of ventricles and decrease in the volume of the whole brain, corpus callosum, globus pallidus and hippocampus. Furthermore, decreased number of parvalbumin-positive inhibitory interneurons was evident in Negr1^−/− hippocampi. Behaviorally, Negr1^−/− mice displayed hyperactivity in social interactions and impairments in social hierarchy. Finally, Negr1 deficiency resulted in disrupted neurite sprouting during neuritogenesis. Our results provide evidence that NEGR1 is required for balancing the ratio of excitatory/inhibitory neurons and proper formation of brain structures, which is prerequisite for adaptive behavioral profiles. Therefore, Negr1^−/− mice have a high potential to provide new insights into the neural mechanisms of neuropsychiatric disorders.

The combined impact of IgLON family proteins Lsamp and Neurotrimin on developing neurons and behavioral profiles in mouse

Cell surface neural adhesion proteins are critical components in the complex orchestration of cell proliferation, apoptosis, and neuritogenesis essential for proper brain construction and behavior. We focused on the impact of two plasticity-associated IgLON family neural adhesion molecules, Neurotrimin (Ntm) and Limbic system associated membrane protein (Lsamp), on mouse behavior and its underlying neural development. Phenotyping neurons derived from the hippocampi of Lsamp^-/-, Ntm^-/- and Lsamp^-/-Ntm^-/- mice was performed in parallel with behavioral testing. While the anatomy of mutant brains revealed no gross changes, the Ntm^-/- hippocampal neurons exhibited premature sprouting of neurites and manifested accelerated neurite elongation and branching. We propose that Ntm exerts an inhibitory impact on neurite outgrowth, whereas Lsamp appears to be an enhancer of the said process as premature neuritogenesis in Ntm^-/- neurons is apparent only in the presence of Lsamp. We also show interplay between Lsamp and Ntm in regulating tissue homeostasis: the impact of Ntm on cellular proliferation was dependent on Lsamp, and Lsamp appeared to be a positive regulator of apoptosis in the presence of Ntm. Behavioral phenotyping indicated test-specific interactions between Lsamp and Ntm. The phenotypes of single mutant lines, such as reduced swimming speed in Morris water maze and increased activity in the elevated plus maze, were magnified in Lsamp^-/-Ntm^-/- mice. Altogether, evidence both from behavioral experiments and cultured hippocampal cells show combined and differential interactions between Ntm and Lsamp in the formation of hippocampal circuits and behavioral profiles. We demonstrate that mutual interactions between IgLON molecules regulate the initiation of neurite sprouting at very early ages, and even cell-autonomously, independent of their regulation of cell-cell adhesion.

Enhancing endogenous capacity to repair a stroke-damaged brain: An evolving field for stroke research

Stroke represents a severe medical condition that causes stroke survivors to suffer from long-term and even lifelong disability. Over the past several decades, a vast majority of stroke research targets neuroprotection in the acute phase, while little work has been done to enhance stroke recovery at the later stage. Through reviewing current understanding of brain plasticity, stroke pathology, and emerging preclinical and clinical restorative approaches, this review aims to provide new insights to advance the research field for stroke recovery. Lifelong brain plasticity offers the long-lasting possibility to repair a stroke-damaged brain. Stroke impairs the structural and functional integrity of entire brain networks; the restorative approaches containing multi-components have great potential to maximize stroke recovery by rebuilding and normalizing the stroke-disrupted entire brain networks and brain functioning. The restorative window for stroke recovery is much longer than previously thought. The optimal time for brain repair appears to be at later stage of stroke rather than the earlier stage. It is expected that these new insights will advance our understanding of stroke recovery and assist in developing the next generation of restorative approaches for enhancing brain repair after stroke.

Glycosylphosphatidylinositol-Anchored Immunoglobulin Superfamily Cell Adhesion Molecules and Their Role in Neuronal Development and Synapse Regulation

Immunoglobulin superfamily (IgSF) cell adhesion molecules (CAMs) are cell surface glycoproteins that not only mediate interactions between neurons but also between neurons and other cells in the nervous system. While typical IgSF CAMs are transmembrane molecules, this superfamily also includes CAMs, which do not possess transmembrane and intracellular domains and are instead attached to the plasma membrane via a glycosylphosphatidylinositol (GPI) anchor. In this review, we focus on the role GPI-anchored IgSF CAMs have as signal transducers and ligands in neurons, and discuss their functions in regulation of neuronal development, synapse formation, synaptic plasticity, learning, and behavior. We also review the links between GPI-anchored IgSF CAMs and brain disorders.

Promoter-Specific Expression and Genomic Structure of IgLON Family Genes in Mouse

IgLON family is composed of five genes: Lsamp, Ntm, Opcml, Negr1, and Iglon5; encoding for five highly homologous neural adhesion proteins that regulate neurite outgrowth and synapse formation. In the current study we performed in silico analysis revealing that Ntm and Opcml display similar genomic structure as previously reported for Lsamp, characterized by two alternative promotors 1a and 1b. Negr1 and Iglon5 transcripts have uniform 5′ region, suggesting single promoter. Iglon5, the recently characterized family member, shares high level of conservation and structural qualities characteristic to IgLON family such as N-terminal signal peptide, three Ig domains, and GPI anchor binding site. By using custom 5′-isoform-specific TaqMan gene-expression assay, we demonstrated heterogeneous expression of IgLON transcripts in different areas of mouse brain and several-fold lower expression in selected tissues outside central nervous system. As an example, the expression of IgLON transcripts in urogenital and reproductive system is in line with repeated reports of urogenital tumors accompanied by mutations in IgLON genes. Considering the high levels of intra-family homology shared by IgLONs, we investigated potential compensatory effects at the level of IgLON isoforms in the brains of mice deficient of one or two family members. We found that the lack of IgLONs is not compensated by a systematic quantitative increase of the other family members. On the contrary, the expression of Ntm 1a transcript and NEGR1 protein was significantly reduced in the frontal cortex of Lsamp-deficient mice suggesting that the expression patterns within IgLON family are balanced coherently. The actions of individual IgLONs, however, can be antagonistic as demonstrated by differential expression of Syp in deletion mutants of IgLONs. In conclusion, we show that the genomic twin-promoter structure has impact on both anatomical distribution and intra-family interactions of IgLON family members. Remarkable variety in the activity levels of 1a and 1b promoters both in the brain and in other tissues, suggests complex functional regulation of IgLONs by alternative signal peptides driven by 1a and 1b promoters.

Deficit in emotional learning in neurotrimin knockout mice

Neurotrimin (Ntm) belongs to the IgLON family of cell adhesion molecules with Lsamp, Obcam and kilon that regulate the outgrowth of neurites mostly by forming heterodimers. IgLONs have been associated with psychiatric disorders, intelligence, body weight, heart disease and tumours. This study provides an initial behavioural and pharmacological characterization of the phenotype of Ntm-deficient mice. We expected to see at least some overlap with the phenotype of Lsamp-deficient mice as Ntm and Lsamp are the main interaction partners in the IgLON family and are colocalized in some brain regions. However, Ntm-deficient mice displayed none of the deviations in behaviour that we have previously shown in Lsamp-deficient mice, but differently from Lsamp-deficient mice, had a deficit in emotional learning in the active avoidance task. The only overlap was decreased sensitivity to the locomotor stimulating effect of amphetamine in both knockout models. Thus, despite being interaction partners, on the behavioural level Lsamp seems to play a much more central role than Ntm and the roles of these two proteins seem to be complementary rather than overlapping.

Cell type- and brain region-resolved mouse brain proteome

Brain transcriptome and connectome maps are being generated, but an equivalent effort on the proteome is currently lacking. We performed high-resolution mass spectrometry-based proteomics for in-depth analysis of the mouse brain and its major brain regions and cell types. Comparisons of the 12,934 identified proteins in oligodendrocytes, astrocytes, microglia and cortical neurons with deep sequencing data of the transcriptome indicated deep coverage of the proteome. Cell type-specific proteins defined as tenfold more abundant than average expression represented about a tenth of the proteome, with an overrepresentation of cell surface proteins. To demonstrate the utility of our resource, we focused on this class of proteins and identified Lsamp, an adhesion molecule of the IgLON family, as a negative regulator of myelination. Our findings provide a framework for a system-level understanding of cell-type diversity in the CNS and serves as a rich resource for analyses of brain development and function.

Gene expression patterns and environmental enrichment-induced effects in the hippocampi of mice suggest importance of Lsamp in plasticity

Limbic system associated membrane protein (Lsamp) gene is involved in behavioral adaptation in social and anxiogenic environments and has been associated with a broad spectrum of psychiatric diseases. Here we studied the activity of alternative promoters of Lsamp gene in mice in three rearing conditions (standard housing, environmental enrichment and social isolation) and in two different genetic backgrounds (129S6/SvEv and C57BL/6). Isolation had no effect on the expression levels of Lsamp. Environmental enrichment elevated the expression levels of Lsamp 1b transcript specifically in the hippocampus in B6 mice, and the same tendency existed across both mouse lines and both transcripts. Furthermore, we showed that the density of cells exhibiting 1b promoter activity is remarkably higher in the subgranular zone of the dentate gyrus in the hippocampal formation which is a specific area of enrichment-induced neurogenesis in adult rodents. On the contrary to 1b, 1a promoter is selectively active in the pyramidal and granule cell layers. We provide evidence that Lsamp modulates enrichment-induced activation of Bdnf as the enrichment-induced elevation of Bdnf in the hippocampus is significantly diminished in Lsamp-deficient mice; furthermore, a significant correlation was found between the expression levels of Lsamp and Bdnf transcripts in the hippocampus and frontal cortex. Significant strain differences in Lsamp expression were detected in the hippocampus, frontal cortex and thalamus that could be related to the different behavioral phenotype of B6 and 129Sv mice. Our data provides further evidence that LSAMP is implicated in the hippocampal connectivity and plasticity thereby modulating adaptability in changing environments.

Subdomain-mediated axon-axon signaling and chemoattraction cooperate to regulate afferent innervation of the lateral habenula

A dominant feature of neural circuitry is the organization of neuronal projections and synapses into specific brain nuclei or laminae. Lamina-specific connectivity is controlled by the selective expression of extracellular guidance and adhesion molecules in the target field. However, how (sub)nucleus-specific connections are established and whether axon-derived cues contribute to subdomain targeting are largely unknown. Here, we demonstrate that the lateral subnucleus of the habenula (lHb) determines its own afferent innervation by sending out efferent projections that express the cell adhesion molecule LAMP to reciprocally collect and guide dopaminergic afferents to the lHb-a phenomenon we term subdomain-mediated axon-axon signaling. This process of reciprocal axon-axon interactions cooperates with lHb-specific chemoattraction mediated by Netrin-1, which controls axon target entry, to ensure specific innervation of the lHb. We propose that cooperation between pretarget reciprocal axon-axon signaling and subdomain-restricted instructive cues provides a highly precise and general mechanism to establish subdomain-specific neural circuitry.

Intercellular protein-protein interactions at synapses

Chemical synapses are asymmetric intercellular junctions through which neurons send nerve impulses to communicate with other neurons or excitable cells. The appropriate formation of synapses, both spatially and temporally, is essential for brain function and depends on the intercellular protein-protein interactions of cell adhesion molecules (CAMs) at synaptic clefts. The CAM proteins link pre- and post-synaptic sites, and play essential roles in promoting synapse formation and maturation, maintaining synapse number and type, accumulating neurotransmitter receptors and ion channels, controlling neuronal differentiation, and even regulating synaptic plasticity directly. Alteration of the interactions of CAMs leads to structural and functional impairments, which results in many neurological disorders, such as autism, Alzheimer's disease and schizophrenia. Therefore, it is crucial to understand the functions of CAMs during development and in the mature neural system, as well as in the pathogenesis of some neurological disorders. Here, we review the function of the major classes of CAMs, and how dysfunction of CAMs relates to several neurological disorders.

Lsamp is implicated in the regulation of emotional and social behavior by use of alternative promoters in the brain

Limbic system-associated membrane protein (LSAMP) is a neural cell adhesion molecule involved in neurite formation and outgrowth. The purpose of the present study was to characterize the distribution of alternatively transcribed Lsamp isoforms in the mouse brain and its implications on the regulation of behavior. Limbic system-associated membrane protein 1b transcript was visualized by using a mouse strain expressing beta-galactosidase under the control of Lsamp 1b promoter. The distribution of Lsamp 1a transcript and summarized expression of the Lsamp transcripts was investigated by non-radioactive in situ RNA hybridization analysis. Cross-validation was performed by using radioactive in situ hybridization with oligonucleotide probes. Quantitative RT-PCR was used to study correlations between the expression of Lsamp isoforms and behavioral parameters. The expression pattern of two promoters differs remarkably from the developmental initiation at embryonic day 12.5. Limbic system-associated membrane protein 1a promoter is active in “classic” limbic structures where the hippocampus and amygdaloid area display the highest expression. Promoter 1b is mostly active in the thalamic sensory nuclei and cortical sensory areas, but also in areas that regulate stress and arousal. Higher levels of Lsamp 1a transcript had significant correlations with all of the measures indicating higher trait anxiety in the elevated plus-maze test. Limbic system-associated membrane protein transcript levels in the hippocampus and ventral striatum correlated with behavioral parameters in the social interaction test. The data are in line with decreased anxiety and alterations in social behavior in Lsamp-deficient mice. We propose that Lsamp is involved in emotional and social operating systems by complex regulation of two alternative promoters.

Quantitative proteomic profiling reveals novel region-specific markers in the adult mouse brain

Despite major advances in neuroscience, a comprehensive understanding of the structural and functional components of the adult brain compartments remains to be fully elucidated at a quantitative molecular level. Indeed, over half of the soluble- and membrane-annotated proteins are currently unmapped within online digital brain atlases. In this study, two complementary approaches were used to assess the unique repertoire of proteins enriched within select regions of the adult mouse CNS, including the brain stem, cerebellum, and remaining brain hemispheres. Of the 1200 proteins visualized by 2D-DIGE, approximately 150 (including cytosolic and membrane proteins) were found to exhibit statistically significant changes in relative abundance thus representing putative region-specific brain markers. In addition to using a high-precision (18) O-labeling strategy for the quantitative LC-MS/MS mapping of membrane proteins isolated from myelin-enriched fractions, we have identified over 1000 proteins that have yet to be described in any other mammalian myelin proteome. A comparison of our myelin proteome was made to an existing transcriptome database containing mRNA abundance profiles during oligodendrocyte differentiation and has confirmed statistically significant abundance changes for ∼500 of these newly mapped proteins, thus revealing new roles in oligodendrocyte and myelin biology. These data offer a resource for the neuroscience community studying the molecular basis for specialized neuronal activities in the CNS and myelin-related disorders. The MS proteomics data associated with this manuscript have been deposited to the ProteomeXchange Consortium with the dataset identifier PXD000327 (http://proteomecentral.proteomexchange.org/dataset/PXD000327).

Limbic system associated membrane protein as a potential target for neuropsychiatric disorders

The studies performed in laboratory animals and psychiatric patients suggest a possible role of limbic system-associated membrane protein (LAMP) in the mechanisms of psychiatric disorders. Stressful manipulations and genetic invalidation have revealed a role of the Lsamp gene in the regulation of anxiety in rodents. Besides that, Lsamp-deficient mice display reduced aggressiveness and impaired adaptation in novel and stressful environments. The behavioral effects of amphetamine were blunted in genetically modified mice. Recent pharmacological and biochemical studies point toward altered function of GABA-, 5-hydroxytryptamine-, and dopaminergic systems in Lsamp-deficient mice. Moreover, we found an association between the gene polymorphisms of LSAMP and major depressive disorder (MDD). Patients suffering from MDD had significantly increased ratio between risk and protective haplotypes of the LSAMP gene compared to healthy volunteers. However, the impact of these haplotypes for the function of LAMP is not clear and remains to be elucidated in future studies.

Functional inactivation of the genome-wide association study obesity gene neuronal growth regulator 1 in mice causes a body mass phenotype

To date, genome-wide association studies (GWAS) have identified at least 32 novel loci for obesity and body mass-related traits. However, the causal genetic variant and molecular mechanisms of specific susceptibility genes in relation to obesity are yet to be fully confirmed and characterised. Here, we examined whether the candidate gene NEGR1 encoding the neuronal growth regulator 1, also termed neurotractin or Kilon, accounts for the obesity association. To characterise the function of NEGR1 for body weight control in vivo, we generated two novel mutant mouse lines, including a constitutive NEGR1-deficient mouse line as well as an ENU-mutagenised line carrying a loss-of-function mutation (Negr1-I87N) and performed metabolic phenotypic analyses. Ablation of NEGR1 results in a small but steady reduction of body mass in both mutant lines, accompanied with a small reduction in body length in the Negr1-I87N mutants. Magnetic resonance scanning reveals that the reduction of body mass in Negr1-I87N mice is due to a reduced proportion of lean mass. Negr1-I87N mutants display reduced food intake and physical activity while normalised energy expenditure remains unchanged. Expression analyses confirmed the brain-specific distribution of NEGR1 including strong expression in the hypothalamus. In vitro assays show that NEGR1 promotes cell-cell adhesion and neurite growth of hypothalamic neurons. Our results indicate a role of NEGR1 in the control of body weight and food intake. This study provides evidence that supports the link of the GWAS candidate gene NEGR1 with body weight control.

Overexpression of IgLON cell adhesion molecules changes proliferation and cell size of cortical astrocytes

IgLON family is a subgroup of the immunoglobulin superfamily cell adhesion molecules and composed of limbic system-associated protein (LAMP), opioid binding cell adhesion molecule (OBCAM), neurotrimin (Ntm) and Kilon. In the present study, we investigated the overexpression of LAMP, OBCAM, Ntm and Kilon on the proliferation and cell size of type-1 astrocytes in vitro. Quantitative analysis using bromodeoxyuridine immunocytochemistry revealed that the expression of OBCAM had greater inhibitory effect on astrocytic proliferation as compared with LAMP, Ntm and Kilon ones. OBCAM overexpression increased the cell size of astrocytes as compared with the control. The treatment of FGF-2 had greater proliferative effect on OBCAM-transfected astrocytes as compared with the control. These results suggest that OBCAM is more potent regulator for controlling the proliferation and cell size of astrocytes as compared with other IgLON proteins possibly through FGF-2 receptor-mediated pathway.

Deletion of the Lsamp gene lowers sensitivity to stressful environmental manipulations in mice

The Lsamp gene gives rise to limbic system-associated membrane protein (LAMP), which is expressed on the surface of somata and proximal dendrites of neurons. Lsamp-deficient mice have been shown to be slightly hyperactive in novel environments and less anxious, and they display alterations in swimming speed, fear reaction, fear conditioning and social behaviour. In human studies, links between the LSAMP gene and several psychiatric disorders have been found and LSAMP has been established as a tumour suppressor gene. To study the impact of environmental manipulations on the phenotype, we exposed male Lsamp-deficient mice to environmental enrichment (EE), a technique that has often been shown to abolish phenotypic deviations in knockout mice, and to social isolation, a stressful manipulation, after which all the mice were tested in a behavioural battery. EE abolished differences between the genotypes in body weight and anogenital sniffing, a behaviour related to aggressiveness, and amplified the anxiolytic-like phenotype of Lsamp-deficient mice both in the plus maze and motility box. Isolation abolished differences between the genotypes in body weight and anxiety and amplified the differences in swimming speed and anogenital sniffing. EE and isolation failed to modify the results as compared to standard housing in whisker trimming, locomotor activity, marble burying and corticosterone levels. In conclusion, Lsamp-deficient mice were less sensitive to isolation stress than their wild-type littermates. Lack of LAMP protein seemingly leads to a deterioration in the ability to adapt to novel stressful environments and stimuli.

IgLONs form heterodimeric complexes on forebrain neurons

IgLONs are a family of four GPI-anchored cell adhesion molecules that regulate neurite outgrowth and synaptogenesis and may act as tumour suppressor genes. Recently we have proposed that two members of the IgLON family act as a heterodimeric complex termed DIgLON. Neurons isolated from chick forebrain co-express all six combinations of IgLONs and the intensity of fluorescence for each pair of IgLONs was highly correlated. Antibody-patching experiments on forebrain neurons show complex formation for IgLON pairs but not between unrelated GPI-anchored glycoproteins. Thus IgLONs are the first GPI-anchored family of glycoproteins shown to form heterodimeric complexes in the plane of the membrane.

NTM and NR3C2 polymorphisms influencing intelligence: family-based association studies

Family, twin, and adoption studies have indicated that human intelligence quotient (IQ) has significant genetic components. We performed a low-density genome-wide association analysis with a family-based association test to identify genetic variants influencing IQ, as measured by Wechsler Adult Intelligence Scale full-score IQ (FSIQ). We examined 11,120 single-nucleotide polymorphisms (SNPs) from the Affymetrix GeneChips 10K mapping array genotyped in 292 nuclear families from Genetic Analysis Workshop 14, a subset from the Collaborative Study on the Genetics of Alcoholism (COGA). A replication analysis was performed using part of International Multi-Center ADHD Genetics Project (IMAGE) dataset. Twenty-two SNPs were identified as having suggestive associations with IQ (p<10(-3)) in the COGA sample and eleven of the SNPs were located within known genes. In particular, NTM at 11q25 (rs411280, p = 0.000764) and NR3C2 at 4q31.1 (rs3846329, p = 0.000675) were two novel genes which have not been associated with IQ in other studies. It has been reported that NTM might play a role in late-onset Alzheimer disease while NR3C2 may be associated with cognitive function and major depression. The associations of these two genes were well-replicated by single-marker and haplotype analyses in the IMAGE sample. In conclusion, our findings provide evidence that chromosome regions of 11q25 and 4q31.1 contain genes affecting IQ. This study will serve as a resource for replication in other populations.

Lower anxiety and a decrease in agonistic behaviour in Lsamp-deficient mice

In rodents, the Lsamp gene has been implicated in trait anxiety, fear reaction and fear conditioning. Human data link the LSAMP gene to several psychiatric disorders. In this study, we presented a general phenotypic characterization of Lsamp gene-deficient mouse line, created by deleting exon 1b. These mice displayed no gross sensory-motor deficiencies, no overt abnormalities and performed normally in memory and learning tests. However, they responded with increased activity to new environments. Moreover, they displayed reduced anxiety and notable deviations in social behaviour, such as lack of whisker trimming, reduced aggressiveness and reduced dominance. One possible explanation for the anxiolytic-like effect of the deletion of the Lsamp gene is a shift in balance in the Gabra1 and Gabra2 genes in the temporal lobe in favor of the Gabra2 transcript, encoding α2 subunit of GABA(A) receptors that mediate the stimulating effect of GABA agonists. The overall phenotype of Lsamp-deficient mice, characterized by decreased anxiety and several alterations in social behaviour, makes them a good model for studying the molecular mechanisms behind inadequate social behaviours observed in several psychiatric disorders.

Loss of limbic system-associated membrane protein leads to reduced hippocampal mineralocorticoid receptor expression, impaired synaptic plasticity, and spatial memory deficit

BACKGROUND

The limbic system-associated membrane protein (LAMP) promotes development of neurons of limbic origin. We have previously shown that genetic deletion of LAMP results in heightened reactivity to novelty and reduced anxiety-like behaviors in mice. Here, we demonstrate a critical role of LAMP in hippocampal-dependent synaptic physiology and behavior.

METHODS

We tested spatial memory performance, hippocampal synaptic plasticity, and stress-related modalities in Lsamp(-/-) mice and their littermate control mice.

RESULTS

Lsamp(-/-) mice exhibit a pronounced deficit in spatial memory acquisition and poorly sustained CA1 long-term potentiation. We found reduced expression of mineralocorticoid receptor (MR) transcripts in the hippocampus and reduction in the corticosterone-induced, MR-mediated nongenomic modulatory effects on CA1 synaptic transmission. Importantly, the impaired long-term potentiation in Lsamp(-/-) mice can be rescued by stress-like levels of corticosterone in a MR-dependent manner.

CONCLUSIONS

Our study reveals a novel functional relationship between a cell adhesion molecule enriched in developing limbic circuits, glucocorticoid receptors, and cognitive functioning.

Glycosylation analysis of IgLON family proteins in rat brain by liquid chromatography and multiple-stage mass spectrometry

IgLON family proteins, including limbic-associated membrane protein (LAMP), opioid-binding cell adhesion molecule (OBCAM), neurotrimin, and Kilon, are immunoglobulin (Ig) superfamily cell adhesion molecules. These molecules are composed of three Ig domains and a glycosylphosphatidylinositol (GPI) anchor and contain six or seven potential N-glycosylation sites. Although their glycosylations are supposed to be associated with the development of the central nervous system like other Ig superfamily proteins, they are still unknown because of difficulty in isolating individual proteins with a high degree of homology in performing carbohydrate analysis. In this study, we conducted simultaneous site-specific glycosylation analysis of rat brain IgLON proteins by liquid chromatography and multiple-stage mass spectrometry (LC-MS ( n )). The rat brain GPI-linked proteins were enriched and separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The four proteins were extracted from the gel, and subjected to LC-MS ( n ) after proteinase digestions. A set of glycopeptide MS data, including the mass spectrum, the mass spectrum in the selected ion monitoring mode, and the product ion spectra, was selected from all data based on carbohydrate-related ions in the MS/MS spectrum. The peptide portion and the carbohydrate structure were identified on the basis of peptide-related ion and carbohydrate-related ions, and the accurate mass. The site-specific glycosylations of four proteins were elucidated as follows. N-Glycans near the N-terminal were disialic acid-conjugated complex- and hybrid-type oligosaccharides. The first Ig domains were occupied by Man-5-9. Diverse oligosaccharides, including Lewis a/x-modified glycans, a brain-specific glycan known as BA-2, and Man-5, were found to be attached to the third Ig domain. Three common structures of glycans were found in the GPI moiety of LAMP, OBCAM, and neurotrimin.

OPCML is a broad tumor suppressor for multiple carcinomas and lymphomas with frequently epigenetic inactivation

BACKGROUND

Identification of tumor suppressor genes (TSGs) silenced by CpG methylation uncovers the molecular mechanism of tumorigenesis and potential tumor biomarkers. Loss of heterozygosity at 11q25 is common in multiple tumors including nasopharyngeal carcinoma (NPC). OPCML, located at 11q25, is one of the downregulated genes we identified through digital expression subtraction.

METHODOLOGY/PRINCIPAL FINDINGS

Semi-quantitative RT-PCR showed frequent OPCML silencing in NPC and other common tumors, with no homozygous deletion detected by multiplex differential DNA-PCR. Instead, promoter methylation of OPCML was frequently detected in multiple carcinoma cell lines (nasopharyngeal, esophageal, lung, gastric, colon, liver, breast, cervix, prostate), lymphoma cell lines (non-Hodgkin and Hodgkin lymphoma, nasal NK/T-cell lymphoma) and primary tumors, but not in any non-tumor cell line and seldom weakly methylated in normal epithelial tissues. Pharmacological and genetic demethylation restored OPCML expression, indicating a direct epigenetic silencing. We further found that OPCML is stress-responsive, but this response is epigenetically impaired when its promoter becomes methylated. Ecotopic expression of OPCML led to significant inhibition of both anchorage-dependent and -independent growth of carcinoma cells with endogenous silencing.

CONCLUSIONS/SIGNIFICANCE

Thus, through functional epigenetics, we identified OPCML as a broad tumor suppressor, which is frequently inactivated by methylation in multiple malignancies.

IgLON cell adhesion molecule Kilon is a crucial modulator for synapse number in hippocampal neurons

Kilon is a member of the IgLON family belonging to the immunoglobulin superfamily of cell adhesion molecules. In the present study, we investigated temporal and spatial changes of Kilon expression and its modulatory functions for synapse number using hippocampal cultured neurons. Kilon was observed to localize chiefly at axons and presynaptic terminals at early culture stage, however, it was seen mainly at dendritic postsynaptic spine of mature neurons at late culture stages. Kilon was solubilized with detergent treatment at early culture stages, while it resisted to extraction of the detergent in mature neurons. The overexpression of Kilon gene using a plasmid vector decreased the number of dendritic synapses at early culture stages, whereas the overexpression increased the number of dendritic synapses at late culture. These results demonstrate the alteration of modulatory function of Kilon for the number of dendritic synapses concomitant with changes in its localization and detergent solubility during neuronal culture development.

Association of limbic system-associated membrane protein (LSAMP) to male completed suicide

Background

Neuroimaging studies have demonstrated volumetric abnormalities in limbic structures of suicide victims. The morphological changes might be caused by some inherited neurodevelopmental defect, such as failure to form proper axonal connections due to genetically determined dysfunction of neurite guidance molecules. Limbic system-associated membrane protein (LSAMP) is a neuronal adhesive molecule, preferentially expressed in developing limbic system neuronal dendrites and somata. Some evidence for the association between LSAMP gene and behavior has come from both animal as well as human studies but further investigation is required. In current study, polymorphic loci in human LSAMP gene were examined in order to reveal any associations between genetic variation in LSAMP and suicidal behaviour.

Methods

DNA was obtained from 288 male suicide victims and 327 healthy male volunteers. Thirty SNPs from LSAMP gene and adjacent region were selected by Tagger algorithm implemented in Haploview 3.32. Genotyping was performed using the SNPlex™ (Applied Biosystems) platform. Data was analyzed by Genemapper 3.7, Haploview 3.32 and SPSS 13.0.

Results

Chi square test revealed four allelic variants (rs2918215, rs2918213, rs9874470 and rs4821129) located in the intronic region of the gene to be associated with suicide, major alleles being overrepresented in suicide group. However, the associations did not survive multiple correction test. Defining the haplotype blocks using confidence interval algorithm implemented in Haploview 3.32, we failed to detect any associated haplotypes.

Conclusion

Despite a considerable amount of investigation on the nature of suicidal behaviour, its aetiology and pathogenesis remain unknown. This study examined the variability in LSAMP gene in relation to completed suicide. Our results indicate that LSAMP might play a role in pathoaetiology of suicidal behaviour but further studies are needed to understand its exact contribution.

Synaptic adhesion molecule OBCAM; synaptogenesis and dynamic internalization

Opioid-binding cell adhesion molecule (OBCAM) is the member of the IgLON family, a subgroup of the immunoglobulin superfamily. In the present study, the functions and dynamics of OBCAM were investigated in hippocampal neurons in vitro. Western blotting revealed that OBCAM expression was low at early stages of culture but it was increased as culture development. Double labeling immunofluorescence microscopy showed that OBCAM immunoreactivity was localized mainly at postsynaptic spines labeled with phalloidin and anti-PSD-95. The inhibition of OBCAM function with the specific antibody resulted in a significant decrease in the number of synapses on dendrites compared with control mouse IgG. The suppression of OBCAM expression using the antisense oligodeoxynucleotide also impaired the formation of synapses compared with control universal ones. The overexpression of OBCAM mRNA using a plasmid vector augmented the formation of synapses. Moreover, the internalization of OBCAM was promoted with increased neuronal activity by 4-aminopyridine. This internalization was reduced with the treatment of filipin, a sterol agent, indicating that this process is a raft-dependent pathway. These results indicate that OBCAM is a synaptic cell adhesion molecule concerning synaptogenesis and its surface localization is dynamically regulated in response to neuronal activity.

Expression of neurotrimin in the normal and injured adult human spinal cord

STUDY DESIGN

Neurotrimin (Ntm) is a member of the family of neural cell adhesion molecules. Its expression pattern suggests that Ntm promotes axonal fasciculation, guides nerve fibers to specific targets and stabilizes synapses as it accumulates coincident with synaptogenesis. Strong labeling of Ntm was observed in motor and sensory areas of the postnatal rat cortex. It is not known whether Ntm is present in adult human spinal cord (SC). In the present study, a monoclonal antibody specific for Ntm (1B1), is applied to the first study of the expression of Ntm in normal and injured adult human SC.

OBJECTIVE

(1) To investigate the expression pattern of Ntm in adult normal human SC, and (2) to observe the changes of Ntm expression after SC injury and compare the differences between normal and injured adult human SC.

METHODS

Human SC tissue was obtained from necropsies of patients with (n=5) and without (n=4) SC injury. The 1B1 Ntm monoclonal antibody was used for immunohistochemical staining on paraffin embedded sections with an ABC kit.

RESULTS

(1) In total, 12 slides were analyzed for each group from both cervical and thoracic levels. Motor neurons and Clarke's neurons and glial-like cells were mild to moderately positive in all uninjured SC specimens. (2) In injured SC, no staining was observed in the injury epicenter between two and three levels proximally and distally, but was detected five levels away. (3) In patients older than 67 years of age, Ntm-positive inclusions were present in the white matter of the SC with or without injury. (4) Some meningeal cells were strongly Ntm-positive, especially in the uninjured human SC.

CONCLUSION

Ntm is expressed by motor and Clarke's neurons and glial cells in uninjured human SC. The downregulation of Ntm in the injured SC suggests that its expression is regulated by afferent input.

Characterization of the genomic structure of the mouse limbic system-associated membrane protein (Lsamp) gene

The Lsamp gene encodes the limbic system-associated membrane protein (LAMP) an immunoglobulin (Ig) superfamily member with three Ig domains and a glycosylphosphatidylinositol anchor. LAMP is expressed by neurons composing the limbic system, is highly conserved between rodents and human, and has structural and functional properties that substantiate its role in the formation of limbic circuits. We report here the genomic organization of the Lsamp gene. The Lsamp gene is composed of 11 exons distributed over 2.2 megabases (Mb). Two exons 1 are separated by approximately 1.6 Mb and contribute to the unusual large size of the gene. Alternative spliced Lsamp mRNAs are generated from distinct promoter regions associated with the two exons 1 that encode distinct signal peptides and thus generate identical native mature polypetides. Additional diversity is created by the use of two small exons to include an insertion of 23 amino acids within the polypeptide C-terminal region of the mature protein. The genomic features of the Lsamp gene described here indicate an intricate mechanism of gene expression regulation that may be relevant in the context of human neuropsychiatric and neurological disorders, where LAMP expression may be altered.

Diglons are heterodimeric proteins composed of IgLON subunits, and Diglon-CO inhibits neurite outgrowth from cerebellar granule cells

IgLONs are a family of four cell adhesion molecules belonging to the Ig superfamily that are thought to play a role in cell-cell recognition and growth-cone migration. One member of the family, opioid-binding cell-adhesion molecule (OBCAM), might act as a tumour suppressor. Previous work has shown that limbic-system-associated protein (LAMP), CEPU-1/Neurotrimin and OBCAM interact homophilically and heterophilically within the family. Here, we show that, based on their relative affinities, CEPU-1 might be both a homo- and a heterophilic cell adhesion molecule, whereas LAMP and OBCAM act only as heterophilic cell adhesion molecules. A binding assay using recombinant IgLONs fused to human Fc showed that IgLONs are organized in the plane of the membrane as heterodimers, and we propose that IgLONs function predominantly as subunits of heterodimeric proteins (Diglons). Thus, the four IgLONs can form six Diglons. Furthermore, although singly transfected cell lines have little effect on neurite outgrowth, CHO cell lines expressing both CEPU-1 and OBCAM (Diglon-CO) inhibit neurite outgrowth from cerebellar granule cells.

Distinct domains of the limbic system-associated membrane protein (LAMP) mediate discrete effects on neurite outgrowth

The limbic system-associated membrane protein (LAMP) is a glycosylphosphatidylinositol-anchored glycoprotein with three immunoglobulin (Ig) domains that can either enhance or inhibit neurite outgrowth depending upon the neuronal population examined. In the present study, we investigate the domains responsible for these activities. Domain deletion revealed that the N-terminal IgI domain is necessary and sufficient for the neurite-promoting activity observed in hippocampal neurons. In contrast, inhibition of neurite outgrowth in SCG neurons, which is mediated by heterophilic interactions, requires full-length LAMP, although selective inhibition of the second Ig domain, but not the first or third domains, prevented the inhibitory effect. This indicates that the IgII domain of LAMP harbors the neurite-inhibiting activity, but only in the context of the full-length configuration. Covasphere-binding analyses demonstrate IgI/IgI interactions, but no interaction between IgII and any other domain, consistent with the biological activities that each domain mediates. The data suggest that LAMP may serve as a bifunctional guidance molecule, with distinct structural domains contributing to the promotion and inhibition of neurite outgrowth.

Dendrite-associated opioid-binding cell adhesion molecule localizes at neurosecretory granules in the hypothalamic magnocellular neurons

Opioid-binding cell adhesion molecule (OBCAM) is a member of the immunoglobulin superfamily containing limbic system-associated membrane protein (IgLON) subgroup of glycosylphosphatidylinositol-anchored immunoglobulin cell adhesion molecules. We have previously found that OBCAM is localized preferentially to dendrites compared with somata and terminals of hypothalamic vasopressin-secreting magnocellular neurons. This localization indicates that OBCAM is one of the dendrite-associated cell adhesion molecules. In the present study, we further characterized the localization and the sorting mechanism, and activity-dependent changes of this molecule in vasopressin-secreting magnocellular dendrites. Confocal microscopic observation revealed the preferential localization of OBCAM at the neurosecretory granules in the vasopressin-positive dendrites. Electron microscopic observation using chromogen-intensified and gold-conjugated methods also demonstrated the OBCAM labeling at most of the neurosecretory granules within the dendrites, while the labeling within the somata was observed at only a few neurosecretory granules. I.c.v. colchicine administration resulted in the disappearance of OBCAM immunoreactivity from the dendrites and in its concomitant accumulation at the somata, suggesting that OBCAM is synthesized at the somata and transported to the dendrites by dendrite-associated neurosecretory granules. During the postnatal development, OBCAM immunoreactivity targeted to vasopressin-positive dendrites became clear from at least 3 weeks after birth, although it appeared at only a few somata 2 weeks after birth. Phosphatidylinositol specific phospholipase C treatment of the membrane fraction of the supraoptic homogenate solubilized OBCAM. Kilon, another IgLON member, was also shown to localize at the neurosecretory granules of vasopressin-positive dendrites via the glycosylphosphatidylinositol anchor. High K(+)-stimulation appeared to cause the diffusion of OBCAM-labeled gold particles from neurosecretory granules together with the exocytosis. These findings indicate that OBCAM is synthesized within the somata, attached to vasopressin neurosecretory granules via the glycosylphosphatidylinositol anchor, and transported to the dendrites. Moreover, the subcellular localization of OBCAM is changed in an activity-dependent manner.