Identification and characterization of two novel brain-derived immunoglobulin superfamily members with a unique structural organization

Mdga2 deficiency leads to an aberrant activation of BDNF/TrkB signaling that underlies autism-relevant synaptic and behavioral changes in mice

Memprin/A5/mu (MAM) domain containing glycosylphosphatidylinositol anchor 2 (MDGA2) is an excitatory synaptic suppressor and its mutations have been associated with autism spectrum disorder (ASD). However, the detailed physiological function of MDGA2 and the mechanism underlying MDGA2 deficiency-caused ASD has yet to be elucidated. Herein, we not only confirm that Mdga2 +/- mice exhibit increased excitatory synapse transmission and ASD-like behaviors, but also identify aberrant brain-derived neurotrophic factor/tyrosine kinase B (BDNF/TrkB) signaling activation in these mice. We demonstrate that MDGA2 interacts with TrkB through its memprin/A5/mu domain, thereby competing the binding of BDNF to TrkB. Both loss of MDGA2 and the ASD-associated MDGA2 V930I mutation promote the BDNF/TrkB signaling activity. Importantly, we demonstrate that inhibiting the BDNF/TrkB signaling by both small molecular compound and MDGA2-derived peptide can attenuate the increase of α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor-mediated excitatory synaptic activity and social deficits in MDGA2-deficient mice. These results highlight a novel MDGA2-BDNF/TrkB-dependent mechanism underlying the synaptic function regulation, which may become a therapeutic target for ASD.

Impaired Hippocampal Long-Term Potentiation and Memory Deficits upon Haploinsufficiency of MDGA1 Can Be Rescued by Acute Administration of D-Cycloserine

The maintenance of proper brain function relies heavily on the balance of excitatory and inhibitory neural circuits, governed in part by synaptic adhesion molecules. Among these, MDGA1 (MAM domain-containing glycosylphosphatidylinositol anchor 1) acts as a suppressor of synapse formation by interfering with Neuroligin-mediated interactions, crucial for maintaining the excitatory-inhibitory (E/I) balance. Mdga1-/- mice exhibit selectively enhanced inhibitory synapse formation in their hippocampal pyramidal neurons, leading to impaired hippocampal long-term potentiation (LTP) and hippocampus-dependent learning and memory function; however, it has not been fully investigated yet if the reduction in MDGA1 protein levels would alter brain function. Here, we examined the behavioral and synaptic consequences of reduced MDGA1 protein levels in Mdga1+/- mice. As observed in Mdga1-/- mice, Mdga1+/- mice exhibited significant deficits in hippocampus-dependent learning and memory tasks, such as the Morris water maze and contextual fear-conditioning tests, along with a significant deficit in the long-term potentiation (LTP) in hippocampal Schaffer collateral CA1 synapses. The acute administration of D-cycloserine, a co-agonist of NMDAR (N-methyl-d-aspartate receptor), significantly ameliorated memory impairments and restored LTP deficits specifically in Mdga1+/- mice, while having no such effect on Mdga1-/- mice. These results highlight the critical role of MDGA1 in regulating inhibitory synapse formation and maintaining the E/I balance for proper cognitive function. These findings may also suggest potential therapeutic strategies targeting the E/I imbalance to alleviate cognitive deficits associated with neuropsychiatric disorders.

MDGA2 Constrains Glutamatergic Inputs Selectively onto CA1 Pyramidal Neurons to Optimize Neural Circuits for Plasticity, Memory, and Social Behavior

Synapse organizers are essential for the development, transmission, and plasticity of synapses. Acting as rare synapse suppressors, the MAM domain containing glycosylphosphatidylinositol anchor (MDGA) proteins contributes to synapse organization by inhibiting the formation of the synaptogenic neuroligin-neurexin complex. A previous analysis of MDGA2 mice lacking a single copy of Mdga2 revealed upregulated glutamatergic synapses and behaviors consistent with autism. However, MDGA2 is expressed in diverse cell types and is localized to both excitatory and inhibitory synapses. Differentiating the network versus cell-specific effects of MDGA2 loss-of-function requires a cell-type and brain region-selective strategy. To address this, we generated mice harboring a conditional knockout of Mdga2 restricted to CA1 pyramidal neurons. Here we report that MDGA2 suppresses the density and function of excitatory synapses selectively on pyramidal neurons in the mature hippocampus. Conditional deletion of Mdga2 in CA1 pyramidal neurons of adult mice upregulated miniature and spontaneous excitatory postsynaptic potentials, vesicular glutamate transporter 1 intensity, and neuronal excitability. These effects were limited to glutamatergic synapses as no changes were detected in miniature and spontaneous inhibitory postsynaptic potential properties or vesicular GABA transporter intensity. Functionally, evoked basal synaptic transmission and AMPAR receptor currents were enhanced at glutamatergic inputs. At a behavioral level, memory appeared to be compromised in Mdga2 cKO mice as both novel object recognition and contextual fear conditioning performance were impaired, consistent with deficits in long-term potentiation in the CA3-CA1 pathway. Social affiliation, a behavioral analog of social deficits in autism, was similarly compromised. These results demonstrate that MDGA2 confines the properties of excitatory synapses to CA1 neurons in mature hippocampal circuits, thereby optimizing this network for plasticity, cognition, and social behaviors.

Upregulation of Spinal MDGA1 in Rats After Nerve Injury Alters Interactions Between Neuroligin-2 and Postsynaptic Scaffolding Proteins and Increases GluR1 Subunit Surface Delivery in the Spinal Cord Dorsal Horn

Previous studies suggested that postsynaptic neuroligin-2 may shift from inhibitory toward excitatory function under pathological pain conditions. We hypothesize that nerve injury may increase the expression of spinal MAM-domain GPI-anchored molecule 1 (MDGA1), which can bind to neuroligin-2 and thereby, alter its interactions with postsynaptic scaffolding proteins and increase spinal excitatory synaptic transmission, leading to neuropathic pain. Western blot, immunofluorescence staining, and co-immunoprecipitation studies were conducted to examine the critical role of MDGA1 in the lumbar spinal cord dorsal horn in rats after spinal nerve ligation (SNL). Small interfering ribonucleic acids (siRNAs) targeting MDGA1 were used to examine the functional roles of MDGA1 in neuropathic pain. Protein levels of MDGA1 in the ipsilateral dorsal horn were significantly upregulated at day 7 post-SNL, as compared to that in naïve or sham rats. The increased levels of GluR1 in the synaptosomal membrane fraction of the ipsilateral dorsal horn tissues at day 7 post-SNL was normalized to near sham level by pretreatment with intrathecal MDGA1 siRNA2308, but not scrambled siRNA or vehicle. Notably, knocking down MDGA1 with siRNAs reduced the mechanical and thermal pain hypersensitivities, and inhibited the increased excitatory synaptic interaction between neuroligin-2 with PSD-95, and prevented the decreased inhibitory postsynaptic interactions between neuroligin-2 and Gephyrin. Our findings suggest that SNL upregulated MDGA1 expression in the dorsal horn, which contributes to the pain hypersensitivity through increasing the net excitatory interaction mediated by neuroligin-2 and surface delivery of GluR1 subunit in dorsal horn neurons.

Synapse organizers as molecular codes for synaptic plasticity

Synapse organizing proteins are multifaceted molecules that coordinate the complex processes of brain development and plasticity at the level of individual synapses. Their importance is demonstrated by the major brain disorders that emerge when their function is compromised. The mechanisms whereby the various families of organizers govern synapses are diverse, but converge on the structure, function, and plasticity of synapses. Therefore, synapse organizers regulate how synapses adapt to ongoing activity, a process central for determining the developmental trajectory of the brain and critical to all forms of cognition. Here, we explore how synapse organizers set the conditions for synaptic plasticity and the associated molecular events, which eventually link to behavioral features of neurodevelopmental and neuropsychiatric disorders. We also propose central questions on how synapse organizers influence network function through integrating nanoscale and circuit-level organization of the brain.

Contrastsing synaptic roles of MDGA1 and MDGA2

Neurodevelopmental disorders are frequently linked to mutations in synaptic organizing molecules. MAM domain containing glycosylphosphatidylinositol anchor 1 and 2 (MDGA1 and MDGA2) are a family of synaptic organizers suggested to play an unusual role as synaptic repressors, but studies offer conflicting evidence for their localization. Using epitope-tagged MDGA1 and MDGA2 knock-in mice, we found that native MDGAs are expressed throughout the brain, peaking early in postnatal development. Surprisingly, endogenous MDGA1 was enriched at excitatory, but not inhibitory, synapses. Both shRNA knockdown and CRISPR/Cas9 knockout of MDGA1 resulted in cell-autonomous, specific impairment of AMPA receptor-mediated synaptic transmission, without affecting GABAergic transmission. Conversely, MDGA2 knockdown/knockout selectively depressed NMDA receptor-mediated transmission but enhanced inhibitory transmission. Our results establish that MDGA2 acts as a synaptic repressor, but only at inhibitory synapses, whereas both MDGAs are required for excitatory transmission. This nonoverlapping division of labor between two highly conserved synaptic proteins is unprecedented.

Peripheral Blood Mononuclear Cell derived Biomarker detection using eXplainable Artificial Intelligence (XAI) provides better diagnosis of Breast Cancer

The incidence and mortality rate of breast cancer increases yearly by an average of 1.44 % and 0.23 %, respectively. Till 2021, there were 7.8 million women who had been diagnosed with breast cancer within 5 years. Biopsies of tumors are often expensive and invasive and raise the risk of serious complications like infection, excessive bleeding, and puncture damage to nearby tissues and organs. Early detection biomarkers are often variably expressed in different patients and may even be below the detection level at an early stage. Hence PBMC that shows alteration in gene profile as a result of interaction with tumor antigens may serve as a better early detection biomarker. Also, such alterations in immune gene profile in PBMCs are more prone to detection despite variability in different breast cancer mutants.This study aimed to identify potential diagnostic biomarkers for breast cancer using eXplainable Artificial Intelligence (XAI) on XGBoost machine learning (ML) models trained on a binary classification dataset containing the expression data of PBMCs from 252 breast cancer patients and 194 healthy women.After effectively adding SHAP values further into the XGBoost model, ten important genes related to breast cancer development were discovered to be effective potential biomarkers. Our studies showed that SVIP, BEND3, MDGA2, LEF1-AS1, PRM1, TEX14, MZB1, TMIGD2, KIT, and FKBP7 are key genes that impact model prediction. These genes may serve as early, non-invasive diagnostic and prognostic biomarkers for breast cancer patients.

Dorsoventral Arrangement of Lateral Hypothalamus Populations in the Mouse Hypothalamus: a Prosomeric Genoarchitectonic Analysis

The lateral hypothalamus (LH) has a heterogeneous cytoarchitectonic organization that has not been elucidated in detail. In this work, we analyzed within the framework of the prosomeric model the differential expression pattern of 59 molecular markers along the ventrodorsal dimension of the medial forebrain bundle in the mouse, considering basal and alar plate subregions of the LH. We found five basal (LH1-LH5) and four alar (LH6-LH9) molecularly distinct sectors of the LH with neuronal cell groups that correlate in topography with previously postulated alar and basal hypothalamic progenitor domains. Most peptidergic populations were restricted to one of these LH sectors though some may have dispersed into a neighboring sector. For instance, histaminergic Hdc-positive neurons were mostly contained within the basal LH3, Nts (neurotensin)- and Tac2 (tachykinin 2)-expressing cells lie strictly within LH4, Hcrt (hypocretin/orexin)-positive and Pmch (pro-melanin-concentrating hormone)-positive neurons appeared within separate LH5 subdivisions, Pnoc (prepronociceptin)-expressing cells were mainly restricted to LH6, and Sst (somatostatin)-positive cells were identified within the LH7 sector. The alar LH9 sector, a component of the Foxg1-positive telencephalo-opto-hypothalamic border region, selectively contained Satb2-expressing cells. Published studies of rodent LH subdivisions have not described the observed pattern. Our genoarchitectonic map should aid in systematic approaches to elucidate LH connectivity and function.

Modulation of Trans-Synaptic Neurexin-Neuroligin Interaction in Pathological Pain

Synapses serve as the interface for the transmission of information between neurons in the central nervous system. The structural and functional characteristics of synapses are highly dynamic, exhibiting extensive plasticity that is shaped by neural activity and regulated primarily by trans-synaptic cell-adhesion molecules (CAMs). Prototypical trans-synaptic CAMs, such as neurexins (Nrxs) and neuroligins (Nlgs), directly regulate the assembly of presynaptic and postsynaptic molecules, including synaptic vesicles, active zone proteins, and receptors. Therefore, the trans-synaptic adhesion mechanisms mediated by Nrx-Nlg interaction can contribute to a range of synaptopathies in the context of pathological pain and other neurological disorders. The present review provides an overview of the current understanding of the roles of Nrx-Nlg interaction in the regulation of trans-synaptic connections, with a specific focus on Nrx and Nlg structures, the dynamic shaping of synaptic function, and the dysregulation of Nrx-Nlg in pathological pain. Additionally, we discuss a range of proteins capable of modulating Nrx-Nlg interactions at the synaptic cleft, with the objective of providing a foundation to guide the future development of novel therapeutic agents for managing pathological pain.

Dysfunction of the Hippocampal-Lateral Septal Circuit Impairs Risk Assessment in Epileptic Mice

Temporal lobe epilepsy, a chronic disease of the brain characterized by degeneration of the hippocampus, has impaired risk assessment. Risk assessment is vital for survival in complex environments with potential threats. However, the underlying mechanisms remain largely unknown. The intricate balance of gene regulation and expression across different brain regions is related to the structure and function of specific neuron subtypes. In particular, excitation/inhibition imbalance caused by hyperexcitability of glutamatergic neurons and/or dysfunction of GABAergic neurons, have been implicated in epilepsy. First, we estimated the risk assessment (RA) by evaluating the behavior of mice in the center of the elevated plus maze, and found that the kainic acid-induced temporal lobe epilepsy mice were specifically impaired their RA. This experiment evaluated approach-RA, with a forthcoming approach to the open arm, and avoid-RA, with forthcoming avoidance of the open arm. Next, results from free-moving electrophysiological recordings showed that in the hippocampus, ∼7% of putative glutamatergic neurons and ∼15% of putative GABAergic neurons were preferentially responsive to either approach-risk assessment or avoid-risk assessment, respectively. In addition, ∼12% and ∼8% of dorsal lateral septum GABAergic neurons were preferentially responsive to approach-risk assessment and avoid-risk assessment, respectively. Notably, during the impaired approach-risk assessment, the favorably activated dorsal dentate gyrus and CA3 glutamatergic neurons increased (∼9%) and dorsal dentate gyrus and CA3 GABAergic neurons decreased (∼7%) in the temporal lobe epilepsy mice. Then, we used RNA sequencing and immunohistochemical staining to investigate which subtype of GABAergic neuron loss may contribute to excitation/inhibition imbalance. The results show that temporal lobe epilepsy mice exhibit significant neuronal loss and reorganization of neural networks. In particular, the dorsal dentate gyrus and CA3 somatostatin-positive neurons and dorsal lateral septum cholecystokinin-positive neurons are selectively vulnerable to damage after temporal lobe epilepsy. Optogenetic activation of the hippocampal glutamatergic neurons or chemogenetic inhibition of the hippocampal somatostatin neurons directly disrupts RA, suggesting that an excitation/inhibition imbalance in the dHPC dorsal lateral septum circuit results in the impairment of RA behavior. Taken together, this study provides insight into epilepsy and its comorbidity at different levels, including molecular, cell, neural circuit, and behavior, which are expected to decrease injury and premature mortality in patients with epilepsy.

Identification of candidate genes on the basis of SNP by time-lagged heat stress interactions for milk production traits in German Holstein cattle

The aim of this study was to estimate genotype by time-lagged heat stress (HS) variance components as well as main and interaction SNP-marker effects for maternal HS during the last eight weeks of cow pregnancy, considering milk production traits recorded in the offspring generation. The HS indicator was the temperature humidity index (THI) for each week. A dummy variable with the code = 1 for the respective week for THI ≥ 60 indicated HS, otherwise, for no HS, the code = 0 was assigned. The dataset included test-day and lactation production traits from 14,188 genotyped first parity Holstein cows. After genotype quality control, 41,139 SNP markers remained for the genomic analyses. Genomic animal models without (model VC_nHS) and with in-utero HS effects (model VC_wHS) were applied to estimate variance components. Accordingly, for genome-wide associations, models GWA_nHS and GWA_wHS, respectively, were applied to estimate main and interaction SNP effects. Common genomic and residual variances for the same traits were very similar from models VC_nHS and VC_wHS. Genotype by HS interaction variances varied, depending on the week with in-utero HS. Among all traits, lactation milk yield with HS from week 5 displayed the largest proportion for interaction variances (0.07). For main effects from model GWA_wHS, 380 SNPs were suggestively associated with all production traits. For the SNP interaction effects from model GWA_wHS, we identified 31 suggestive SNPs, which were located in close distance to 62 potential candidate genes. The inferred candidate genes have various biological functions, including mechanisms of immune response, growth processes and disease resistance. Two biological processes excessively represented in the overrepresentation tests addressed lymphocyte and monocyte chemotaxis, ultimately affecting immune response. The modelling approach considering time-lagged genotype by HS interactions for production traits inferred physiological mechanisms being associated with health and immunity, enabling improvements in selection of robust animals.

Application of Single Nucleotide Polymorphism Microarray in Prenatal Diagnosis of Fetuses with Central Nervous System Abnormalities

Background

The current gold standard of karyotype analysis for prenatal diagnosis of fetuses with central nervous system (CNS) abnormalities has some limitations. Here, we assessed the value of single nucleotide polymorphism (SNP) arrays as a diagnostic tool.

Methods

The results of prenatal diagnosis of 344 fetuses with CNS abnormalities as determined by ultrasonographic screening were retrospectively analyzed. All fetuses underwent chromosomal karyotype analysis and genome-wide SNP array analysis simultaneously. The resultant rates and frequencies of genomic abnormalities were compared.

Results

Karyotype analysis found 45 (13.2%) abnormal CNS cases, while SNP array found 60 (17.4%) cases. SNP array detected 23 (6.7%) cases of submicroscopic abnormalities that karyotype analysis did not find. The detection rate of karyotype analysis was 8.1% in the group with isolated CNS anomalies, but 16.5% in the group with CNS abnormalities plus extra ultrasound anomalies. Detection rates of SNP array were 12.4% and 20.8% in these two groups, respectively. Statistical analysis showed that the detection rates of both methods were significantly higher in the group with CNS malformations and other ultrasound anomalies than in the group with isolated CNS anomalies. Abnormal chromosomes were detected most frequently in fetuses with holoprosencephaly.

Conclusion

Genome-wide SNP array technology can significantly improve the positive detection rate of fetuses with CNS abnormalities. Combining karyotype analysis and SNP array technology is recommended for detecting the development of fetuses with abnormal CNS.

Comparative mapping of selected structural determinants on the extracellular domains of cholinesterase-like cell-adhesion molecules

Cell adhesion generally involves formation of homophilic or heterophilic protein complexes between two cells to form transcellular junctions. Neural cell-adhesion members of the α/β-hydrolase fold superfamily of proteins use their extracellular or soluble cholinesterase-like domain to bind cognate partners across cell membranes, as illustrated by the neuroligins. These cell-adhesion molecules currently comprise the synaptic organizers neuroligins found in all animal phyla, along with three proteins found only in invertebrates: the guidance molecule neurotactin, the glia-specific gliotactin, and the basement membrane protein glutactin. Although these proteins share a cholinesterase-like fold, they lack one or more residues composing the catalytic triad responsible for the enzymatic activity of the cholinesterases. Conversely, they are found in various subcellular localisations and display specific disulfide bonding and N-glycosylation patterns, along with individual surface determinants possibly associated with recognition and binding of protein partners. Formation of non-covalent dimers typical of the cholinesterases is documented for mammalian neuroligins, yet whether invertebrate neuroligins and their neurotactin, gliotactin and glutactin relatives also form dimers in physiological conditions is unknown. Here we provide a brief overview of the localization, function, evolution, and conserved versus individual structural determinants of these cholinesterase-like cell-adhesion proteins. This article is part of the special issue entitled 'Acetylcholinesterase Inhibitors: From Bench to Bedside to Battlefield'.

Interplay between Anakonda, Gliotactin, and M6 for Tricellular Junction Assembly and Anchoring of Septate Junctions in Drosophila Epithelium

In epithelia, tricellular junctions (TCJs) serve as pivotal sites for barrier function and integration of both biochemical and mechanical signals [1-3]. In Drosophila, TCJs are composed of the transmembrane protein Sidekick at the adherens junction (AJ) level, which plays a role in cell-cell contact rearrangement [4-6]. At the septate junction (SJ) level, TCJs are formed by Gliotactin (Gli) [7], Anakonda (Aka) [8, 9], and the Myelin proteolipid protein (PLP) M6 [10, 11]. Despite previous data on TCJ organization [12-14], TCJ assembly, composition, and links to adjacent bicellular junctions (BCJs) remain poorly understood. Here, we have characterized the making of TCJs within the plane of adherens junctions (tricellular adherens junction [tAJ]) and the plane of septate junctions (tricellular septate junction [tSJ]) and report that their assembly is independent of each other. Aka and M6, whose localizations are interdependent, act upstream to localize Gli. In turn, Gli stabilizes Aka at tSJ. Moreover, tSJ components are not only essential at vertex, as we found that loss of tSJ integrity induces micron-length bicellular SJ (bSJ) deformations. This phenotype is associated with the disappearance of SJ components at tricellular contacts, indicating that bSJs are no longer connected to tSJs. Reciprocally, SJ components are required to restrict the localization of Aka and Gli at vertex. We propose that tSJs function as pillars to anchor bSJs to ensure the maintenance of tissue integrity in Drosophila proliferative epithelia.

MDGA1-deficiency attenuates prepulse inhibition with alterations of dopamine and serotonin metabolism: An ex vivo HPLC-ECD analysis

MDGA1 (MAM domain-containing glycosylphosphatidylinositol anchor) has recently been linked to schizophrenia and bipolar disorder. Dysregulation of dopamine (DA) and serotonin (5-HT) systems has long been associated with schizophrenia and other neuropsychiatric disorders. Here, we measured prepulse inhibition (PPI) of the startle response and ex vivo tissue content of monoamines and their metabolites in the frontal cortex, striatum and hippocampus of Mdga1 homozygous (Mdga1-KO), Mdga1 heterozygous (Mdga1-HT) and wild-type (WT) male mice. We found that Mdga1-KO mice exhibited statistically significant impairment of PPI, and had higher levels of homovanillic acid in all three brain regions studied compared with Mdga1-HT and WT mice (P < 0.05), while levels of norepinephrine, DA and its metabolites 3,4-dihydroxyphenylacetic acid and 3-methoxytyramine remained unchanged. Mdga1-KO mice also had a lower 5-hydroxyindoleacetic acid level in the striatum (P < 0.05) compared with WT mice. 5-HT levels remained unchanged with the exception of a significant increase in the level in the cortex. These data are the first evidence suggesting that MDGA1 deficiency leads to a pronounced deficit in PPI and plays an important role in perturbation of DA and 5-HT metabolism in mouse brain; such changes may contribute to a range of neuropsychiatric disorders.

A negative regulator of synaptic development: MDGA and its links to neurodevelopmental disorders

BACKGROUND

Formation of protein complexes across synapses is a critical process in neurodevelopment, having direct implications on brain function and animal behavior. Here, we present the understanding, importance, and potential impact of a newly found regulator of such a key interaction.

DATA SOURCES

A systematic search of the literature was conducted on PubMed (Medline), Embase, and Central-Cochrane Database.

RESULTS

Membrane-associated mucin domain-containing glycosylphosphatidylinositol anchor proteins (MDGAs) were recently discovered to regulate synaptic development and transmission via suppression of neurexins-neuroligins trans-synaptic complex formation. MDGAs also regulate axonal migration and outgrowth. In the context of their physiological role, we begin to consider the potential links to the etiology of certain neurodevelopmental disorders. We present the gene expression and protein structure of MDGAs and discuss recent progress in our understanding of the neurobiological role of MDGAs to explore its potential as a therapeutic target.

CONCLUSION

MDGAs play a key role in neuron migration, axon guidance and synapse development, as well as in regulating brain excitation and inhibition balance.

Identifying loci under positive selection in complex population histories

Detailed modeling of a species' history is of prime importance for understanding how natural selection operates over time. Most methods designed to detect positive selection along sequenced genomes, however, use simplified representations of past histories as null models of genetic drift. Here, we present the first method that can detect signatures of strong local adaptation across the genome using arbitrarily complex admixture graphs, which are typically used to describe the history of past divergence and admixture events among any number of populations. The method-called graph-aware retrieval of selective sweeps (GRoSS)-has good power to detect loci in the genome with strong evidence for past selective sweeps and can also identify which branch of the graph was most affected by the sweep. As evidence of its utility, we apply the method to bovine, codfish, and human population genomic data containing panels of multiple populations related in complex ways. We find new candidate genes for important adaptive functions, including immunity and metabolism in understudied human populations, as well as muscle mass, milk production, and tameness in specific bovine breeds. We are also able to pinpoint the emergence of large regions of differentiation owing to inversions in the history of Atlantic codfish.

Loss of Synapse Repressor MDGA1 Enhances Perisomatic Inhibition, Confers Resistance to Network Excitation, and Impairs Cognitive Function

Synaptopathies contributing to neurodevelopmental disorders are linked to mutations in synaptic organizing molecules, including postsynaptic neuroligins, presynaptic neurexins, and MDGAs, which regulate their interaction. The role of MDGA1 in suppressing inhibitory versus excitatory synapses is controversial based on in vitro studies. We show that genetic deletion of MDGA1 in vivo elevates hippocampal CA1 inhibitory, but not excitatory, synapse density and transmission. Furthermore, MDGA1 is selectively expressed by pyramidal neurons and regulates perisomatic, but not distal dendritic, inhibitory synapses. Mdga1^-/- hippocampal networks demonstrate muted responses to neural excitation, and Mdga1^-/- mice are resistant to induced seizures. Mdga1^-/- mice further demonstrate compromised hippocampal long-term potentiation, consistent with observed deficits in spatial and context-dependent learning and memory. These results suggest that mutations in MDGA1 may contribute to cognitive deficits through altered synaptic transmission and plasticity by loss of suppression of inhibitory synapse development in a subcellular domain- and cell-type-selective manner.

Pumping the brakes: suppression of synapse development by MDGA-neuroligin interactions

Synapse development depends on a dynamic balance between synapse promoters and suppressors. MDGAs, immunoglobulin superfamily proteins, negatively regulate synapse development through blocking neuroligin-neurexin interactions. Recent analyses of MDGA-neuroligin complexes revealed the structural basis of this activity and indicate that MDGAs interact with all neuroligins with differential affinities. Surprisingly, analyses of mouse mutants revealed a functional divergence, with targeted mutation of Mdga1 and Mdga2 elevating inhibitory and excitatory synapses, respectively, on hippocampal pyramidal neurons. Further research is needed to determine the synapse-specific organizing properties of MDGAs in neural circuits, which may depend on relative levels and subcellular distributions of each MDGA, neuroligin and neurexin. Behavioral deficits in Mdga mutant mice support genetic links to schizophrenia and autism spectrum disorders and raise the possibility of harnessing these interactions for therapeutic purposes.

Immunoglobulin-Like Receptors and Their Impact on Wiring of Brain Synapses

Synapse formation is mediated by a surprisingly large number and wide variety of genes encoding many different protein classes. One of the families increasingly implicated in synapse wiring is the immunoglobulin superfamily (IgSF). IgSF molecules are by definition any protein containing at least one Ig-like domain, making this family one of the most common protein classes encoded by the genome. Here, we review the emerging roles for IgSF molecules in synapse formation specifically in the vertebrate brain, focusing on examples from three classes of IgSF members: ( a) cell adhesion molecules, ( b) signaling molecules, and ( c) immune molecules expressed in the brain. The critical roles for IgSF members in regulating synapse formation may explain their extensive involvement in neuropsychiatric and neurodevelopmental disorders. Solving the IgSF code for synapse formation may reveal multiple new targets for rescuing IgSF-mediated deficits in synapse formation and, eventually, new treatments for psychiatric disorders caused by altered IgSF-induced synapse wiring.

The caudo-ventral pallium is a novel pallial domain expressing Gdf10 and generating Ebf3-positive neurons of the medial amygdala

In rodents, the medial nucleus of the amygdala receives direct inputs from the accessory olfactory bulbs and is mainly implicated in pheromone-mediated reproductive and defensive behaviors. The principal neurons of the medial amygdala are GABAergic neurons generated principally in the caudo-ventral medial ganglionic eminence and preoptic area. Beside GABAergic neurons, the medial amygdala also contains glutamatergic Otp-expressing neurons cells generated in the lateral hypothalamic neuroepithelium and a non-well characterized Pax6-positive population. In the present work, we describe a novel glutamatergic Ebf3-expressing neuronal subpopulation distributed within the periphery of the postero-ventral medial amygdala. These neurons are generated in a pallial domain characterized by high expression of Gdf10. This territory is topologically the most caudal tier of the ventral pallium and accordingly, we named it Caudo-Ventral Pallium (CVP). In the absence of Pax6, the CVP is disrupted and Ebf3-expressing neurons fail to be generated. Overall, this work proposes a novel model of the neuronal composition of the medial amygdala and unravels for the first time a new novel pallial subpopulation originating from the CVP and expressing the transcription factor Ebf3.

Synaptic Neurexin Complexes: A Molecular Code for the Logic of Neural Circuits

Synapses are specialized junctions between neurons in brain that transmit and compute information, thereby connecting neurons into millions of overlapping and interdigitated neural circuits. Here, we posit that the establishment, properties, and dynamics of synapses are governed by a molecular logic that is controlled by diverse trans-synaptic signaling molecules. Neurexins, expressed in thousands of alternatively spliced isoforms, are central components of this dynamic code. Presynaptic neurexins regulate synapse properties via differential binding to multifarious postsynaptic ligands, such as neuroligins, cerebellin/GluD complexes, and latrophilins, thereby shaping the input/output relations of their resident neural circuits. Mutations in genes encoding neurexins and their ligands are associated with diverse neuropsychiatric disorders, especially schizophrenia, autism, and Tourette syndrome. Thus, neurexins nucleate an overall trans-synaptic signaling network that controls synapse properties, which thereby determines the precise responses of synapses to spike patterns in a neuron and circuit and which is vulnerable to impairments in neuropsychiatric disorders.

Structural Mechanism for Modulation of Synaptic Neuroligin-Neurexin Signaling by MDGA Proteins

Neuroligin-neurexin (NL-NRX) complexes are fundamental synaptic organizers in the central nervous system. An accurate spatial and temporal control of NL-NRX signaling is crucial to balance excitatory and inhibitory neurotransmission, and perturbations are linked with neurodevelopmental and psychiatric disorders. MDGA proteins bind NLs and control their function and interaction with NRXs via unknown mechanisms. Here, we report crystal structures of MDGA1, the NL1-MDGA1 complex, and a spliced NL1 isoform. Two large, multi-domain MDGA molecules fold into rigid triangular structures, cradling a dimeric NL to prevent NRX binding. Structural analyses guided the discovery of a broad, splicing-modulated interaction network between MDGA and NL family members and helped rationalize the impact of autism-linked mutations. We demonstrate that expression levels largely determine whether MDGAs act selectively or suppress the synapse organizing function of multiple NLs. These results illustrate a potentially brain-wide regulatory mechanism for NL-NRX signaling modulation.

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

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

Tracing the dynamics of gene transcripts after organismal death

In life, genetic and epigenetic networks precisely coordinate the expression of genes-but in death, it is not known if gene expression diminishes gradually or abruptly stops or if specific genes and pathways are involved. We studied this by identifying mRNA transcripts that apparently increase in relative abundance after death, assessing their functions, and comparing their abundance profiles through postmortem time in two species, mouse and zebrafish. We found mRNA transcript profiles of 1063 genes became significantly more abundant after death of healthy adult animals in a time series spanning up to 96 h postmortem. Ordination plots revealed non-random patterns in the profiles by time. While most of these transcript levels increased within 0.5 h postmortem, some increased only at 24 and 48 h postmortem. Functional characterization of the most abundant transcripts revealed the following categories: stress, immunity, inflammation, apoptosis, transport, development, epigenetic regulation and cancer. The data suggest a step-wise shutdown occurs in organismal death that is manifested by the apparent increase of certain transcripts with various abundance maxima and durations.

MDGA2 is a novel tumour suppressor cooperating with DMAP1 in gastric cancer and is associated with disease outcome

BACKGROUND

Using the promoter methylation assay, we have shown that MDGA2 (MAM domain containing glycosylphosphatidylinositol anchor 2) is preferentially methylated in gastric cancer. We analysed its biological effects and prognostic significance in gastric cancer.

METHODS

MDGA2 methylation status was evaluated by combined bisulfite restriction analysis and bisulfite genomic sequencing. The effects of MDGA2 re-expression or knockdown on cell proliferation, apoptosis and the cell cycle were determined. MDGA2 interacting protein was identified by mass spectrometry and MDGA2-related cancer pathways by reporter activity and PCR array analyses. The clinical impact of MDGA2 was assessed in 218 patients with gastric cancer.

RESULTS

MDGA2 was commonly silenced in gastric cancer cells (10/11) and primary gastric cancers due to promoter hypermethylation. MDGA2 significantly inhibited cell proliferation by causing G1-S cell cycle arrest and inducing cell apoptosis in vitro, and suppressed xenograft tumour growth in both subcutaneous and orthotopic xenograft mouse models (both p<0.001). The anti-tumorigenic effect of MDGA2 was mediated through direct stabilising of DNA methyltransferase 1 associated protein 1 (DMAP1), which played a tumour suppressive role in gastric cancer. This interaction activated their downstream key elements of p53/p21 signalling cascades. Moreover, promoter methylation of MDGA2 was detected in 62.4% (136/218) of gastric cancers. Multivariate analysis showed that patients with MDGA2 hypermethylation had a significantly decreased survival (p=0.005). Kaplan-Meier survival curves showed that MDGA2 hypermethylation was significantly associated with shortened survival in patients with early gastric cancer.

CONCLUSIONS

MDGA2 is a critical tumour suppressor in gastric carcinogenesis; its hypermethylation is an independent prognostic factor in patients with gastric cancer.

Regulation of GABAergic synapse development by postsynaptic membrane proteins

In the adult mammalian brain, GABAergic neurotransmission provides the majority of synaptic inhibition that balances glutamatergic excitatory drive and thereby controls neuronal output. It is generally accepted that synaptogenesis is initiated through highly specific protein-protein interactions mediated by membrane proteins expressed in developing presynaptic terminals and postsynaptic membranes. Accumulating studies have uncovered a number of membrane proteins that regulate different aspects of GABAergic synapse development. In this review, we summarize recent advances in understanding of GABAergic synapse development with a focus on postsynaptic membrane molecules, including receptors, synaptogenic cell adhesion molecules and immunoglobulin superfamily proteins.

Formation of the Cortical Subventricular Zone Requires MDGA1-Mediated Aggregation of Basal Progenitors

The subventricular zone (SVZ) provides a specialized neurogenic microenvironment for proliferation and aggregation of basal progenitors (BPs). Our study reveals a mechanism for the aggregation of BPs within the SVZ required for their proliferation and generation of cortical layer neurons. The autism-related IgCAM, MDGA1, is locally expressed in the BP cell membrane where it co-localizes and complexes with the gap junction protein Connexin43. To address MDGA1 function, we created a floxed allele of MDGA1 and deleted it from BPs. MDGA1 deletion results in reduced BP proliferation and size of the SVZ, with an aberrant population of BPs ectopically positioned in the cortical plate. These defects are manifested in diminished production of cortical layer neurons and a significant reduction of the cortical layers. We conclude that MDGA1 functions to aggregate and maintain BPs within the SVZ providing the neurogenic niche required for their proliferation and generation of cortical layer neurons.

The balancing act of GABAergic synapse organizers

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

Proper migration and axon outgrowth of zebrafish cranial motoneuron subpopulations require the cell adhesion molecule MDGA2A

The formation of functional neuronal circuits relies on accurate migration and proper axonal outgrowth of neuronal precursors. On the route to their targets migrating cells and growing axons depend on both, directional information from neurotropic cues and adhesive interactions mediated via extracellular matrix molecules or neighbouring cells. The inactivation of guidance cues or the interference with cell adhesion can cause severe defects in neuronal migration and axon guidance. In this study we have analyzed the function of the MAM domain containing glycosylphosphatidylinositol anchor 2A (MDGA2A) protein in zebrafish cranial motoneuron development. MDGA2A is prominently expressed in distinct clusters of cranial motoneurons, especially in the ones of the trigeminal and facial nerves. Analyses of MDGA2A knockdown embryos by light sheet and confocal microscopy revealed impaired migration and aberrant axonal outgrowth of these neurons; suggesting that adhesive interactions mediated by MDGA2A are required for the proper arrangement and outgrowth of cranial motoneuron subtypes.

Deleted copy number variation of Hanwoo and Holstein using next generation sequencing at the population level

BACKGROUND

Copy number variation (CNV), a source of genetic diversity in mammals, has been shown to underlie biological functions related to production traits. Notwithstanding, there have been few studies conducted on CNVs using next generation sequencing at the population level.

RESULTS

Illumina NGS data was obtained for ten Holsteins, a dairy cattle, and 22 Hanwoo, a beef cattle. The sequence data for each of the 32 animals varied from 13.58-fold to almost 20-fold coverage. We detected a total of 6,811 deleted CNVs across the analyzed individuals (average length = 2732.2 bp) corresponding to 0.74% of the cattle genome (18.6 Mbp of variable sequence). By examining the overlap between CNV deletion regions and genes, we selected 30 genes with the highest deletion scores. These genes were found to be related to the nervous system, more specifically with nervous transmission, neuron motion, and neurogenesis. We regarded these genes as having been effected by the domestication process. Further analysis of the CNV genotyping information revealed 94 putative selected CNVs and 954 breed-specific CNVs.

CONCLUSIONS

This study provides useful information for assessing the impact of CNVs on cattle traits using NGS at the population level.

The neuroligins and their ligands: from structure to function at the synapse

The neuroligins are cell adhesion proteins whose extracellular domain belongs to the α/β-hydrolase fold family of proteins, mainly containing enzymes and exemplified by acetylcholinesterase. The ectodomain of postsynaptic neuroligins interacts through a calcium ion with the ectodomain of presynaptic neurexins to form flexible trans-synaptic associations characterized by selectivity for neuroligin or neurexin subtypes. This heterophilic interaction, essential for synaptic differentiation, maturation, and maintenance, is regulated by gene selection, alternative mRNA splicing, and posttranslational modifications. Mutations leading to deficiencies in the expression, folding, maturation, and binding properties of either partner are associated with autism spectrum disorders. The currently available structural and functional data illustrate how these two families of cell adhesion molecules bridge the synaptic cleft to participate in synapse plasticity and support its dynamic nature. Neuroligin partners distinct from the neurexins, and which may undergo either trans or cis interaction, have also been described, and tridimensional structures of some of them are available. Our study emphasizes the partnership versatility of the neuroligin ectodomain associated with molecular flexibility and alternative binding sites, proposes homology models of the structurally non-characterized neuroligin partners, and exemplifies the large structural variability at the surface of the α/β-hydrolase fold subunit. This study also provides new insights into possible surface binding sites associated with non-catalytic properties of the acetylcholinesterase subunit.

Significance of glycosylphosphatidylinositol-anchored protein enrichment in lipid rafts for the control of autoimmunity

Glycosylphosphatidylinositols (GPI) are complex glycolipids that are covalently linked to the C terminus of proteins as a post-translational modification and tether proteins to the plasma membrane. One of the most striking features of GPI-anchored proteins (APs) is their enrichment in lipid rafts. The biosynthesis of GPI and its attachment to proteins occur in the endoplasmic reticulum. In the Golgi, GPI-APs are subjected to fatty acid remodeling, which replaces an unsaturated fatty acid at the sn-2 position of the phosphatidylinositol moiety with a saturated fatty acid. We previously reported that fatty acid remodeling is critical for the enrichment of GPI-APs in lipid rafts. To investigate the biological significance of GPI-AP enrichment in lipid rafts, we generated a PGAP3 knock-out mouse (PGAP3(-/-)) in which fatty acid remodeling of GPI-APs does not occur. We report here that a significant number of aged PGAP3(-/-) mice developed autoimmune-like symptoms, such as increased anti-DNA antibodies, spontaneous germinal center formation, and enlarged renal glomeruli with deposition of immune complexes and matrix expansion. A possible cause for this was the impaired engulfment of apoptotic cells by resident peritoneal macrophages in PGAP3(-/-) mice. Mice with conditional targeting of PGAP3 in either B or T cells did not develop such autoimmune-like symptoms. In addition, PGAP3(-/-) mice exhibited the tendency of Th2 polarization. These data demonstrate that PGAP3-dependent fatty acid remodeling of GPI-APs has a significant role in the control of autoimmunity, possibly by the regulation of apoptotic cell clearance and Th1/Th2 balance.

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

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

MDGAs interact selectively with neuroligin-2 but not other neuroligins to regulate inhibitory synapse development

The MAM domain-containing GPI anchor proteins MDGA1 and MDGA2 are Ig superfamily adhesion molecules composed of six IG domains, a fibronectin III domain, a MAM domain, and a GPI anchor. MDGAs contribute to the radial migration and positioning of a subset of cortical neurons during early neural development. However, MDGAs continue to be expressed in postnatal brain, and their functions during postnatal neural development remain unknown. Here, we demonstrate that MDGAs specifically and with a nanomolar affinity bind to neuroligin-2, a cell-adhesion molecule of inhibitory synapses, but do not bind detectably to neuroligin-1 or neuroligin-3. We observed no cell adhesion between cells expressing neuroligin-2 and MDGA1, suggesting a cis interaction. Importantly, RNAi-mediated knockdown of MDGAs increased the abundance of inhibitory but not excitatory synapses in a neuroligin-2-dependent manner. Conversely, overexpression of MDGA1 decreased the numbers of functional inhibitory synapses. Likewise, coexpression of both MDGA1 and neuroligin-2 reduced the synaptogenic capacity of neuroligin-2 in an artificial synapse-formation assay by abolishing the ability of neuroligin-2 to form an adhesion complex with neurexins. Taken together, our data suggest that MDGAs inhibit the activity of neuroligin-2 in controlling the function of inhibitory synapses and that MDGAs do so by binding to neuroligin-2.

Genome-wide association study of SSRI/SNRI-induced sexual dysfunction in a Japanese cohort with major depression

Sexual dysfunction is a major side effect of selective serotonin reuptake inhibitors (SSRIs) and serotonin-noradrenaline reuptake inhibitors (SNRIs). We conducted a genome-wide association study to identify the genetic factors contributing to the risk of SSRI/SNRI-induced sexual dysfunction by testing 186 320 single nucleotide polymorphism (SNP) markers in a cohort of 201 Japanese major depression patients including 36 with sexual dysfunction induced by SSRI (paroxetine or fluvoxamine) or SNRI (milnacipran). The Cochran-Armitage trend test showed that 11 SNPs, tightly clustered in a distinct region on chromosome 14q21.3, were associated with SSRI/SNRI-induced sexual dysfunction at a genome-wide significance level after false discovery rate (FDR) correction, and the strongest SNP association was with rs1160351 (P=3.04 × 10(-7), risk ratio=2.92, 95% confidence interval (CI)=1.79-4.76). These SNPs mapped to the intronic region of the MDGA2 gene. A Manhattan plot showed that the strong association peak remained in MDGA2 after adjustment for sex and age in a multivariable logistic regression analysis although P values increased slightly and became non-significant. Replication studies with larger sample sizes are required to validate this exploratory study, but our findings may provide insights into the genetic basis of sexual dysfunction induced by SSRI/SNRI.

Transgene insertion in intronic sequences of Mdga2 gene shows methylation in an imprinted manner in an Acrodysplasia (Adp) mouse line

The Acrodysplasia (Adp) mutation arises from the insertion of a transgene containing a mouse metallothionein-promoted bovine papilloma virus and human growth hormone-releasing factor gene. Although the transgene is not expressed, mice that are hemizygous for the transgene show skull and paw deformities when the progeny receive the transgene paternally. To elucidate the molecular mechanisms underlying the mutant phenotype and the modified transmission pattern of the Adp phenotype, a junctional fragment around the transgene integration site was cloned. The transgene was inserted into the intronic sequences between exon 3 and exon 4 of the Mdga2 gene and the degree of methylation of the transgene and the severity of the phenotype were reciprocally related in that the transgene was highly or under methylated in normal and deformed mice, respectively. Thus, methylation of the transgene appears to regulate phenotypic expression and imprinting of Adp.

Single-nucleotide polymorphisms of MAMDC1 are associated with rash and photosensitivity, but not disease risk, of systemic lupus erythematosus in Chinese mainland population

Systemic lupus erythematosus (SLE) is a complex immune disease affected by both genetic dispositions and environmental factors. Recently, the polymorphisms in MAMDC1 gene have been reported to associate with disease risk of SLE in European population. However, whether this association is replicated in Chinese population is unknown yet. A total of 491 SLE patients and 533 controls were recruited. Unlabeled probe-based high-resolution melting analysis (HRMA) was used in genotyping. HRMA with unlabeled probe successfully distinguished all genotypes. SNP rs961616 was associated with rash [P = 0.015, odds ratio (OR) = 0.73, 95% confidence interval (CI) = 0.57-0.94] and photosensitivity (P = 0.001, OR = 0.63, 95%CI = 0.48-0.84), but not the disease risk (P = 0.133, OR = 0.88, 95%CI = 0.74-1.04), of SLE in Chinese population. Polymorphisms of rs961616 in MAMDC1 gene were associated with rash and photosensitivity, but not disease risk, of systemic lupus erythematosus in Chinese population.

IgSF molecule MDGA1 is involved in radial migration and positioning of a subset of cortical upper-layer neurons

Mdga1, encoding a GPI-anchored immunoglobulin superfamily molecule containing an MAM domain, is expressed by a specific subset of neurons, including layer II/III projection neurons, in the mouse neocortex. To investigate the function of Mdga1 in corticogenesis, we generated Mdga1-deficient mice and backcrossed them to obtain a congenic background. Gross anatomy of the Mdga1-deficient brain at postnatal day (P) 14 showed no obvious phenotype. However, the migration of Mdga1-mutant neurons to the superficial cortical plate was clearly delayed. Most Mdga1-mutant neurons reached the lower portion of the upper cortical layer by embryonic day 18.5 and stayed there through P0. By P7, the location of the mutant cells was the same as wild-type. The location of Cux2-expressing upper-layer neurons in the cortical plate was largely unaffected. These observations indicated that Mdga1 is involved in the migration and positioning of a subset of cortical neurons and suggested that the radial migration of upper-layer neurons might be differentially regulated.

Rostral growth of commissural axons requires the cell adhesion molecule MDGA2

Background

Long-distance axonal growth relies on the precise interplay of guidance cues and cell adhesion molecules. While guidance cues provide positional and directional information for the advancing growth cone, cell adhesion molecules are essential in enabling axonal advancement. Such a dependence on adhesion as well as guidance molecules can be well observed in dorsal commissural interneurons, which follow a highly stereotypical growth and guidance pattern. The mechanisms and molecules involved in the attraction and outgrowth towards the ventral midline, the axon crossing towards the contralateral side, the rostral turning after midline crossing as well as the guidance along the longitudinal axis have been intensely studied. However, little is known about molecules that provide the basis for commissural axon growth along the anterior-posterior axis.

Results

MDGA2, a recently discovered cell adhesion molecule of the IgCAM superfamily, is highly expressed in dorsolaterally located (dI1) spinal interneurons. Functional studies inactivating MDGA2 by RNA interference (RNAi) or function-blocking antibodies demonstrate that either treatment results in a lack of commissural axon growth along the longitudinal axis. Moreover, results from RNAi experiments targeting the contralateral side together with binding studies suggest that homophilic MDGA2 interactions between ipsilaterally projecting axons and post-crossing commissural axons may be the basis of axonal growth along the longitudinal axis.

Conclusions

Directed axonal growth of dorsal commissural interneurons requires an elaborate mixture of instructive (guidance) and permissive (outgrowth supporting) molecules. While Wnt and Sonic hedgehog (Shh) signalling pathways have been shown to specify the growth direction of post-crossing commissural axons, our study now provides evidence that homophilic MDGA2 interactions are essential for axonal extension along the longitudinal axis. Interestingly, so far each part of the complex axonal trajectory of commissural axons uses its own set of guidance and growth-promoting molecules, possibly explaining why such a high number of molecules influencing the growth pattern of commissural interneurons has been identified.

The MDGA1 gene confers risk to schizophrenia and bipolar disorder

OBJECTIVE

The structural, cytoarchitectural and functional brain abnormalities reported in patients with mental disorders may be due to aberrant neuronal migration influenced by cell adhesion molecules. MDGA1, like Ig-containing cell adhesion molecules, has several cell adhesion molecule-like domains. Moreover, Kahler et al. (2008) reported that the MDGA1 gene was a schizophrenia susceptibility gene in Scandinavian population. To further investigate whether the MDGA1 gene is a shared risk factor of schizophrenia, bipolar disorder and major depressive disorder in Chinese Han population, we conducted this study.

METHODS

We recruited 1135 unrelated schizophrenia patients, 1135 unrelated bipolar disorder patients, 1135 unrelated major depressive disorder patients and 1135 unrelated controls of Chinese Han origin. A total of eleven common SNPs were genotyped using TaqMan® technology.

RESULTS

The genotype frequency of rs11759115 differed significantly between schizophrenia patients and controls. The C-C haplotype of rs11759115-rs7769372 was also positively associated with schizophrenia (permutated p=0.046). Rs1883901 was found to be positively associated with bipolar disorder (allele: permutated p=0.0085; genotype: permutated p=0.0009; OR=1.31 [95%CI=1.12-1.52]). The A-G-G haplotype of rs1883901-rs10807187-rs9462343 was also positively associated with bipolar disorder with a global p value of 0.0391 after permutations. No individual SNP or haplotype was associated with major depressive disorder after permutations.

CONCLUSION

The MDGA1 gene may confer risk to schizophrenia and bipolar disorder in Chinese Han population.

Control of neural interfacing in peripheral nerves through regenerative molecular guidance

Regenerative peripheral nerve interfaces have been proposed as viable alternatives for the natural control of robotic prosthetic devices. However, random axonal pathfinding during peripheral nerve regeneration leads to mixed populations of sensory and motor neurons at the electrode interfaces preventing the precise identification of the modality nature of the recorded action potentials; motor or specific sensory sub-modalities. This study present evidence that supports the notion that type-specific neurotrophins can be used to preferentially entice and segregate the growth of defined axonal populations from transected peripheral nerves. Segregation of mixed sensory fibers from dorsal root ganglion neurons was evaluated in vitro by compartmentalized diffusion delivery of nerve growth factor (NGF) and neurotrophin-3 (NT-3), to preferentially entice the growth of trkA+ nociceptive and trkC+ proprioceptive subsets of sensory neurons, respectively.

Expression of Human MDGA1 Increases Cell Motility and Cell-Cell Adhesion and Reduces Adhesion to Extracellular Matrix Proteins in MDCK Cells

Characterization of the novel human protein MDGA1 (MAM Domain containing Glycosylphosphatidylinositol Anchor-1) has been reported in our laboratory in the past few years. hMDGA1 is a glycoprotein containing 955 aminoacids (137 kDa) attached to the eukaryotic cell membrane by a GPI (Glycosylphosphatidylinositol) anchor and localized specifically into membrane microdomains known as lipid rafts. Moreover, MDGA1 protein contains structural features found in different types of cell adhesion molecules (CAMs) such as the presence of immunoglobulin domains and a MAM domain (Meprin, A5 protein, receptor protein-tyrosine phosphatase μ), suggesting a role of MDGA1 in cell migration and/or adhesion. In order to investigate this aim, stable MDCK cell lines expressing MDGA1 or the truncated proteins IgGPI (lacking the MAM domain) and MAMGPI (lacking Ig domains) were generated. Our results reveal that MDGA1 increases the ability of MDCK cells to migrate, as it contains both Ig and MAM domains which have been implicated in cell motility. In addition, cell adhesion to extracellular matrix proteins, mainly to collagen IV, is reduced by MDGA1 and the IgGPI and MAMGPI truncated proteins. Accordingly, silencing MDGA1 by siRNA revealed a significant increase in adhesion to collagen IV. Furthermore, MDGA1 expression, through the intrinsic properties of the MAM domain, increases cell-cell adhesion independently of the cell monolayer used, suggesting that MDGA1 mediates cell-cell adhesiveness in a heterophilic manner.

Identification of MAMDC1 as a candidate susceptibility gene for systemic lupus erythematosus (SLE)

Background

Systemic lupus erythematosus (SLE) is a complex autoimmune disorder with multiple susceptibility genes. We have previously reported suggestive linkage to the chromosomal region 14q21-q23 in Finnish SLE families.

Principal Findings

Genetic fine mapping of this region in the same family material, together with a large collection of parent affected trios from UK and two independent case-control cohorts from Finland and Sweden, indicated that a novel uncharacterized gene, MAMDC1 (MAM domain containing glycosylphosphatidylinositol anchor 2, also known as MDGA2, MIM 611128), represents a putative susceptibility gene for SLE. In a combined analysis of the whole dataset, significant evidence of association was detected for the MAMDC1 intronic single nucleotide polymorphisms (SNP) rs961616 (P –value = 0.001, Odds Ratio (OR) = 1.292, 95% CI 1.103–1.513) and rs2297926 (P –value = 0.003, OR = 1.349, 95% CI 1.109–1.640). By Northern blot, real-time PCR (qRT-PCR) and immunohistochemical (IHC) analyses, we show that MAMDC1 is expressed in several tissues and cell types, and that the corresponding mRNA is up-regulated by the pro-inflammatory cytokines tumour necrosis factor alpha (TNF-α) and interferon gamma (IFN-γ) in THP-1 monocytes. Based on its homology to known proteins with similar structure, MAMDC1 appears to be a novel member of the adhesion molecules of the immunoglobulin superfamily (IgCAM), which is involved in cell adhesion, migration, and recruitment to inflammatory sites. Remarkably, some IgCAMs have been shown to interact with ITGAM, the product of another SLE susceptibility gene recently discovered in two independent genome wide association (GWA) scans.

Significance

Further studies focused on MAMDC1 and other molecules involved in these pathways might thus provide new insight into the pathogenesis of SLE.

Imprinting analysis in the Acrodysplasia region of mouse chromosome 12

The insertional mouse mutation Adp (Acrodysplasia) confers a parent-of-origin developmental phenotype, with animals inheriting the mutation from their father showing skeletal abnormalities, whereas those inheriting the mutation from their mother are normal. This parental-specific phenotype, along with mapping of the insertion to a region of chromosome 12 proposed to contain imprinted genes, suggested that disruption of genomic imprinting might underlie the Adp phenotype. Genomic imprinting is the process by which autosomal genes are epigenetically silenced on one of the two parental alleles; imprinting mutation phenotypes manifest after inheritance from one parent but not the other. Imprinted genes typically occur in dense clusters that contain few non-imprinted genes and therefore representative genes from the Adp critical region could be assayed to identify any imprinted domains. None of the genes analysed were found to be imprinted, however, suggesting that other explanations for the Adp phenotype must be considered.

Characterization of teleost Mdga1 using a gene-trap approach in medaka (Oryzias latipes)

MAM domain containing glycosilphosphatidilinositol anchor 1 (MDGA1) is an IgCAM protein present in many vertebrate species including humans. In mammals, MDGA1 is expressed by a subset of neurons in the developing brain and thought to function in neural cell migration. We identified a fish ortholog of mdga1 by a gene-trap screen utilizing the Frog Prince transposon in medaka (Japanese killifish, Oryzias latipes). The gene-trap vector was inserted into an intronic region of mdga1 to form a chimeric protein with green fluorescent protein, allowing us to monitor mdga1 expression in vivo. Expression of medaka mdga1 was seen in various types of embryonic brain neurons, and specifically in neurons migrating toward their target sites, supporting the proposed function of MDGA1. We also isolated the closely related mdga2 gene, whose expression partially overlapped with that of mdga1. Despite the fact that the gene-trap event eliminated most of the functional domains of the Mdga1 protein, homozygous embryos developed normally without any morphological abnormality, suggesting a functional redundancy of Mdga1 with other related proteins. High sequential homology of MDGA proteins between medaka and other vertebrate species suggests an essential role of the MDGA gene family in brain development among the vertebrate phylum.

Genome-wide analyses of exonic copy number variants in a family-based study point to novel autism susceptibility genes

The genetics underlying the autism spectrum disorders (ASDs) is complex and remains poorly understood. Previous work has demonstrated an important role for structural variation in a subset of cases, but has lacked the resolution necessary to move beyond detection of large regions of potential interest to identification of individual genes. To pinpoint genes likely to contribute to ASD etiology, we performed high density genotyping in 912 multiplex families from the Autism Genetics Resource Exchange (AGRE) collection and contrasted results to those obtained for 1,488 healthy controls. Through prioritization of exonic deletions (eDels), exonic duplications (eDups), and whole gene duplication events (gDups), we identified more than 150 loci harboring rare variants in multiple unrelated probands, but no controls. Importantly, 27 of these were confirmed on examination of an independent replication cohort comprised of 859 cases and an additional 1,051 controls. Rare variants at known loci, including exonic deletions at NRXN1 and whole gene duplications encompassing UBE3A and several other genes in the 15q11-q13 region, were observed in the course of these analyses. Strong support was likewise observed for previously unreported genes such as BZRAP1, an adaptor molecule known to regulate synaptic transmission, with eDels or eDups observed in twelve unrelated cases but no controls (p = 2.3x10(-5)). Less is known about MDGA2, likewise observed to be case-specific (p = 1.3x10(-4)). But, it is notable that the encoded protein shows an unexpectedly high similarity to Contactin 4 (BLAST E-value = 3x10(-39)), which has also been linked to disease. That hundreds of distinct rare variants were each seen only once further highlights complexity in the ASDs and points to the continued need for larger cohorts.