Schizophrenia and affective disorders--cosegregation with a translocation at chromosome 1q42 that directly disrupts brain-expressed genes: clinical and P300 findings in a family

Association of schizophrenia with the rs821633 polymorphism in the DISC1 gene among Han Chinese

BACKGROUND

Previous studies report that various single nucleotide polymorphisms (SNP) in the Disrupted-in Schizophrenia 1 (DISC1) gene are closely associated with schizophrenia, but there are no studies that assess the relationship of age of onset of schizophrenia with these SNPs.

OBJECTIVE

Investigate the relationship between the rs821633 SNP in the DISC1 gene and the occurrence and age of onset of schizophrenia in Han Chinese.

METHODS

We used the TaqMan genotyping technology to examine the rs821633 SNP in the DISC1 gene among 315 individuals who developed schizophrenia prior to 19 years of age ('early-onset'), 407 individuals who developed schizophrenia when 19 years of age or older ('late-onset'), and 482 healthy controls. We used survival analyses to investigate the relationship between the rs821633(C) risk allele and the age of onset of schizophrenia.

RESULTS

Compared to the prevalence in healthy controls, the prevalence of the C/C genotype of rs821633 and of the C allele in rs821633 were significantly greater in individuals with early-onset schizophrenia (X (2)=7.17, df=1, p=0.007; X (2)=7.20, df=2, p=0.032) and significantly greater in individuals with late-onset schizophrenia (X (2)=5.36, df=1, p=0.022; X (2)=6.58, df=2, p=0.041). However, there were no significant differences in the prevalence of the C/C genotype or the C allele between individuals with early-onset and late-onset schizophrenia. Kaplan-Meier survival analyses found no significant association between the rs821633(C) risk allele and age of onset in schizophrenia.

CONCLUSION

We confirm the association of polymorphism in the rs821633 SNP in the DISC1 gene with schizophrenia among Han Chinese, but we found no association between the rs821633(C) risk allele and the age of onset in individuals with schizophrenia.

Synaptic activity: An emerging player in schizophrenia

Schizophrenia is a polygenic disorder with a complex etiology. While the genetic and molecular underpinnings of the disease are poorly understood, variations in genes encoding synaptic pathways are consistently implicated. Although its impact is still an open question, a deficit in synaptic activity provides an attractive model to explain the cognitive etiology of schizophrenia. Recent advances in high-throughput imaging and functional studies bring new hope for the application of in vitro disease modeling with patient-derived neurons to empirically ascertain the extent to which these synaptic pathways are involved in the disease. In addition, the emergent avenue of research targeted to probe neuronal connections is revealing critical insight into circuitry and may influence how we think about psychiatric disorders in the near future. This article is part of a Special Issue entitled SI: Exploiting human neurons.

Imaging genetics and psychiatric disorders

Imaging genetics is an integrated research method that uses neuroimaging and genetics to assess the impact of genetic variation on brain function and structure. Imaging genetics is both a tool for the discovery of risk genes for psychiatric disorders and a strategy for characterizing the neural systems affected by risk gene variants to elucidate quantitative and mechanistic aspects of brain function implicated in psychiatric disease. Early studies of imaging genetics included association analyses between brain morphology and single nucleotide polymorphisms whose function is well known, such as catechol-Omethyltransferase (COMT) and brain-derived neurotrophic factor (BDNF). GWAS of psychiatric disorders have identified genes with unknown functions, such as ZNF804A, and imaging genetics has been used to investigate clues of the biological function of these genes. The difficulty in replicating the findings of studies with small sample sizes has motivated the creation of largescale collaborative consortiums, such as ENIGMA, CHARGE and IMAGEN, to collect thousands of images. In a genome-wide association study, the ENIGMA consortium successfully identified common variants in the genome associated with hippocampal volume at 12q24, and the CHARGE consortium replicated this finding. The new era of imaging genetics has just begun, and the next challenge we face is the discovery of small effect size signals from large data sets obtained from genetics and neuroimaging. New methods and technologies for data reduction with appropriate statistical thresholds, such as polygenic analysis and parallel independent component analysis (ICA), are warranted. Future advances in imaging genetics will aid in the discovery of genes and provide mechanistic insight into psychiatric disorders.

Molecular Pathways Underlying Projection Neuron Production and Migration during Cerebral Cortical Development

Glutamatergic neurons of the mammalian cerebral cortex originate from radial glia (RG) progenitors in the ventricular zone (VZ). During corticogenesis, neuroblasts migrate toward the pial surface using two different migration modes. One is multipolar (MP) migration with random directional movement, and the other is locomotion, which is a unidirectional movement guided by the RG fiber. After reaching their final destination, the neurons finalize their migration by terminal translocation, which is followed by maturation via dendrite extension to initiate synaptogenesis and thereby complete neural circuit formation. This switching of migration modes during cortical development is unique in mammals, which suggests that the RG-guided locomotion mode may contribute to the evolution of the mammalian neocortical 6-layer structure. Many factors have been reported to be involved in the regulation of this radial neuronal migration process. In general, the radial migration can be largely divided into four steps; (1) maintenance and departure from the VZ of neural progenitor cells, (2) MP migration and transition to bipolar cells, (3) RG-guided locomotion, and (4) terminal translocation and dendrite maturation. Among these, many different gene mutations or knockdown effects have resulted in failure of the MP to bipolar transition (step 2), suggesting that it is a critical step, particularly in radial migration. Moreover, this transition occurs at the subplate layer. In this review, we summarize recent advances in our understanding of the molecular mechanisms underlying each of these steps. Finally, we discuss the evolutionary aspects of neuronal migration in corticogenesis.

A New Outlook on Mental Illnesses: Glial Involvement Beyond the Glue

Mental illnesses have long been perceived as the exclusive consequence of abnormalities in neuronal functioning. Until recently, the role of glial cells in the pathophysiology of mental diseases has largely been overlooked. However recently, multiple lines of evidence suggest more diverse and significant functions of glia with behavior-altering effects. The newly ascribed roles of astrocytes, oligodendrocytes and microglia have led to their examination in brain pathology and mental illnesses. Indeed, abnormalities in glial function, structure and density have been observed in postmortem brain studies of subjects diagnosed with mental illnesses. In this review, we discuss the newly identified functions of glia and highlight the findings of glial abnormalities in psychiatric disorders. We discuss these preclinical and clinical findings implicating the involvement of glial cells in mental illnesses with the perspective that these cells may represent a new target for treatment.

Neuroanatomical correlates of attitudes toward suicide in a large healthy sample: A voxel-based morphometric analysis

Previous studies have indicated that permissive attitudes toward suicide are positively associated with mental illness (e.g., depression and loneliness). Evidence suggests that there are abnormalities in the cognitive and brain functioning of suicidal patients. Nevertheless, there has been no evidence of the correlation between attitudes toward suicide and abnormal brain structure variations in healthy people. Therefore, in this study, we seek to investigate the neuroanatomical differences in healthy participants with regard to attitudes toward suicide. The results show that permissive attitudes toward suicide were significantly correlated with gray matter volume (GMV) in the left dorsolateral prefrontal cortex (DLPFC) and the left cerebellum in the large sample (n=405), which may be related to inefficient inhibitory control of negative emotion. Then, in a subset of healthy individuals with permissive attitudes (n=113), we also observed that stronger permissive attitudes toward suicide were positively related to the larger GMV in the left DLPFC and the left middle temporal gyrus (MTG), which may be associated with sensitivity of emotional feeling. Furthermore, loneliness had a mediating effect on the relation between the DLPFC volume and attitudes toward suicide. Taken together, neuroanatomical differences in healthy participants with permissive attitudes toward suicide may provide a better understanding of permissive attitudes toward suicide as a likely risk factor for suicidal behavior.

New discoveries in schizophrenia genetics reveal neurobiological pathways: A review of recent findings

Schizophrenia research has undergone a recent transformation. By leveraging large sample sizes, genome-wide association studies of common genetic variants have approximately tripled the number of candidate genetic loci. Rare variant studies have identified copy number variants that are schizophrenia risk loci. Among these, the 3q29 microdeletion is now known to be the single largest schizophrenia risk factor. Next-generation sequencing studies are increasingly used for rare variant association testing, and have already facilitated identification of large effect alleles. Collectively, recent findings implicate voltage-gated calcium channel and cytoskeletal pathways in the pathogenesis of schizophrenia. Taken together, these results suggest the possibility of imminent breakthroughs in the molecular understanding of schizophrenia.

Copy Number Variations in DISC1 and DISC1-Interacting Partners in Major Mental Illness

Robust statistical, genetic and functional evidence supports a role for DISC1 in the aetiology of major mental illness. Furthermore, many of its protein-binding partners show evidence for involvement in the pathophysiology of a range of neurodevelopmental and psychiatric disorders. Copy number variants (CNVs) are suspected to play an important causal role in these disorders. In this study, CNV analysis of DISC1 and its binding partners PAFAH1B1, NDE1, NDEL1, FEZ1, MAP1A, CIT and PDE4B in Scottish and Northern Swedish population-based samples was carried out using multiplex amplicon quantification. Here, we report the finding of rare CNVs in DISC1, NDE1 (together with adjacent genes within the 16p13.11 duplication), NDEL1 (including the overlapping MYH10 gene) and CIT. Our findings provide further evidence for involvement of DISC1 and its interaction partners in neuropsychiatric disorders and also for a role of structural variants in the aetiology of these devastating diseases.

DISC1 Protein Regulates γ-Aminobutyric Acid, Type A (GABAA) Receptor Trafficking and Inhibitory Synaptic Transmission in Cortical Neurons

Association studies have suggested that Disrupted-in-Schizophrenia 1 (DISC1) confers a genetic risk at the level of endophenotypes that underlies many major mental disorders. Despite the progress in understanding the significance of DISC1 at neural development, the mechanisms underlying DISC1 regulation of synaptic functions remain elusive. Because alterations in the cortical GABA system have been strongly linked to the pathophysiology of schizophrenia, one potential target of DISC1 that is critically involved in the regulation of cognition and emotion is the GABAA receptor (GABAAR). We found that cellular knockdown of DISC1 significantly reduced GABAAR-mediated synaptic and whole-cell current, whereas overexpression of wild-type DISC1, but not the C-terminal-truncated DISC1 (a schizophrenia-related mutant), significantly increased GABAAR currents in pyramidal neurons of the prefrontal cortex. These effects were accompanied by DISC1-induced changes in surface GABAAR expression. Moreover, the regulation of GABAARs by DISC1 knockdown or overexpression depends on the microtubule motor protein kinesin 1 (KIF5). Our results suggest that DISC1 exerts an important effect on GABAergic inhibitory transmission by regulating KIF5/microtubule-based GABAAR trafficking in the cortex. The knowledge gained from this study would shed light on how DISC1 and the GABA system are linked mechanistically and how their interactions are critical for maintaining a normal mental state.

Associating schizophrenia, long non-coding RNAs and neurostructural dynamics

Several lines of evidence indicate that schizophrenia has a strong genetic component. But the exact nature and functional role of this genetic component in the pathophysiology of this mental illness remains a mystery. Long non-coding RNAs (lncRNAs) are a recently discovered family of molecules that regulate gene transcription through a variety of means. Consequently, lncRNAs could help us bring together apparent unrelated findings in schizophrenia; namely, genomic deficiencies on one side and neuroimaging, as well as postmortem results on the other. In fact, the most consistent finding in schizophrenia is decreased brain size together with enlarged ventricles. This anomaly appears to originate from shorter and less ramified dendrites and axons. But a decrease in neuronal arborizations cannot explain the complex pathophysiology of this psychotic disorder; however, dynamic changes in neuronal structure present throughout life could. It is well recognized that the structure of developing neurons is extremely plastic. This structural plasticity was thought to stop with brain development. However, breakthrough discoveries have shown that neuronal structure retains some degree of plasticity throughout life. What the neuroscientific field is still trying to understand is how these dynamic changes are regulated and lncRNAs represent promising candidates to fill this knowledge gap. Here, we present evidence that associates specific lncRNAs with schizophrenia. We then discuss the potential role of lncRNAs in neurostructural dynamics. Finally, we explain how dynamic neurostructural modifications present throughout life could, in theory, reconcile apparent unrelated findings in schizophrenia.

Searching human brain for mechanisms of psychiatric disorders. Implications for studies on schizophrenia

In the past 25years, research on the human brain has been providing a clear path toward understanding the pathophysiology of psychiatric illnesses. The successes that have been accrued are matched by significant difficulties identifying and controlling a large number of potential confounding variables. By systematically and effectively accounting for unwanted variance in data from imaging and postmortem human brain studies, meaningful and reliable information regarding the pathophysiology of human brain disorders can be obtained. This perspective paper focuses on postmortem investigations to discuss some of the most challenging sources of variance, including diagnosis, comorbidity, substance abuse and pharmacological treatment, which confound investigations of the human brain.

The cortical thickness phenotype of individuals with DISC1 translocation resembles schizophrenia

BACKGROUND. The disrupted in schizophrenia 1 (DISC1) gene locus was originally identified in a Scottish pedigree with a high incidence of psychiatric disorders that is associated with a balanced t(1;11)(q42.1;q14.3) chromosomal translocation. Here, we investigated whether members of this family carrying the t(1;11)(q42.1;q14.3) translocation have a common brain-related phenotype and whether this phenotype is similar to that observed in schizophrenia (SCZ), using multivariate pattern recognition techniques.

METHODS. We measured cortical thickness, cortical surface area, subcortical volumes, and regional cerebral blood flow (rCBF) in healthy controls (HC) (n = 24), patients diagnosed with SCZ (n = 24), patients diagnosed with bipolar disorder (BP) (n = 19), and members of the original Scottish family (n = 30) who were either carriers (T+) or noncarriers (T–) of the DISC1 translocation. Binary classification models were developed to assess the differences and similarities across groups.

RESULTS. Based on cortical thickness, 72% of the T– group were assigned to the HC group, 83% of the T+ group were assigned to the SCZ group, and 45% of the BP group were classified as belonging to the SCZ group, suggesting high specificity of this measurement in predicting brain-related phenotypes. Shared brain-related phenotypes between SCZ and T+ individuals were found for cortical thickness only. Finally, a classification accuracy of 73% was achieved when directly comparing the pattern of cortical thickness of T+ and T– individuals.

CONCLUSION. Together, the results of this study suggest that the DISC1 translocation may increase the risk of psychiatric disorders in this pedigree by affecting neurostructural phenotypes such as cortical thickness.

FUNDING. This work was supported by the National Health Service Research Scotland, the Scottish Translational Medicine Research Collaboration, the Innovative Medicines Initiative (IMI), the Engineering and Physical Sciences Research Council (EPSRC), The Wellcome Trust, the National Institute of Health Research (NIHR), and Pfizer.

Genomic DISC1 Disruption in hiPSCs Alters Wnt Signaling and Neural Cell Fate

Genetic and clinical association studies have identified disrupted in schizophrenia 1 (DISC1) as a candidate risk gene for major mental illness. DISC1 is interrupted by a balanced chr(1;11) translocation in a Scottish family in which the translocation predisposes to psychiatric disorders. We investigate the consequences of DISC1 interruption in human neural cells using TALENs or CRISPR-Cas9 to target the DISC1 locus. We show that disruption of DISC1 near the site of the translocation results in decreased DISC1 protein levels because of nonsense-mediated decay of long splice variants. This results in an increased level of canonical Wnt signaling in neural progenitor cells and altered expression of fate markers such as Foxg1 and Tbr2. These gene expression changes are rescued by antagonizing Wnt signaling in a critical developmental window, supporting the hypothesis that DISC1-dependent suppression of basal Wnt signaling influences the distribution of cell types generated during cortical development.

Longitudinal investigation of the relationship between family history of psychosis and affective disorders and Child Behavior Checklist ratings in clinical high-risk adolescents

This is the first study to investigate whether positive family history (FH) of psychosis and affective disorders moderates the relationship between child diagnostic status and parent-reported social and behavioral problems on the Child Behavior Checklist (CBCL) in clinical high-risk adolescents. This longitudinal investigation assessed 122 participants (mean age=14.25±1.8years) from three groups (at-risk, other personality disorders, non-psychiatric controls) at baseline and one year follow-up. As predicted, there was a main effect of FH for a number of CBCL scales indicating higher scores for adolescents with positive FH. The findings also demonstrate a significant Diagnostic Status×Family History interaction for several behavioral scales providing support for FH as a concurrent and longitudinal moderator of the relationship between diagnostic status and CBCL scales. The moderating effect is present for areas of functioning associated with depression, anxiety, social adjustment, thought problems, attention problems, and aggressive behavior. The findings also indicate that both positive and negative symptoms are related to the genetic vulnerability for developing psychosis in clinical high-risk individuals, particularly those symptoms reflective of emotional, attentional, and interpersonal functioning. The present findings are novel and have significant clinical and research implications. This investigation provides a platform for future studies to clarify further the role of FH in clinical high-risk individuals and contributes to integration of this knowledge in the development of early intervention and prevention approaches in at-risk populations for the emergence of severe mental illness.

DISC1-mediated dysregulation of adult hippocampal neurogenesis in rats

Adult hippocampal neurogenesis, the constitutive generation of new granule cells in the dentate gyrus of the mature brain, is a robust model of neural development and its dysregulation has been implicated in the pathogenesis of psychiatric and neurological disorders. Previous studies in mice have shown that altered expression of Disrupted-In-Schizophrenia 1 (Disc1), the mouse homolog of a risk gene for major psychiatric disorders, results in several distinct morphological phenotypes during neuronal development. Although there are advantages to using rats over mice for neurophysiological studies, genetic manipulations have not been widely utilized in rat models. Here, we used a retroviral-mediated approach to knockdown DISC1 expression in dividing cells in the rat dentate gyrus and characterized the morphological development of adult-born granule neurons. Consistent with earlier findings in mice, we show that DISC1 knockdown in adult-born dentate granule cells in rats resulted in accelerated dendritic growth, soma hypertrophy, ectopic dendrites, and mispositioning of new granule cells due to overextended migration. Our study thus demonstrates that the Disc1 genetic manipulation approach used in prior mouse studies is feasible in rats and that there is a conserved biological function of this gene across species. Extending gene-based studies of adult hippocampal neurogenesis from mice to rats will allow for the development of additional models that may be more amenable to behavioral and in vivo electrophysiological investigations. These models, in turn, can generate additional insight into the systems-level mechanisms of how risk genes for complex psychiatric disorders may impact adult neurogenesis and hippocampal function.

Effects of a Balanced Translocation between Chromosomes 1 and 11 Disrupting the DISC1 Locus on White Matter Integrity

Objective

Individuals carrying rare, but biologically informative genetic variants provide a unique opportunity to model major mental illness and inform understanding of disease mechanisms. The rarity of such variations means that their study involves small group numbers, however they are amongst the strongest known genetic risk factors for major mental illness and are likely to have large neural effects. DISC1 (Disrupted in Schizophrenia 1) is a gene containing one such risk variant, identified in a single Scottish family through its disruption by a balanced translocation of chromosomes 1 and 11; t(1;11) (q42.1;q14.3).

Method

Within the original pedigree, we examined the effects of the t(1;11) translocation on white matter integrity, measured by fractional anisotropy (FA). This included family members with (n = 7) and without (n = 13) the translocation, along with a clinical control sample of patients with psychosis (n = 34), and a group of healthy controls (n = 33).

Results

We report decreased white matter integrity in five clusters in the genu of the corpus callosum, the right inferior fronto-occipital fasciculus, acoustic radiation and fornix. Analysis of the mixed psychosis group also demonstrated decreased white matter integrity in the above regions. FA values within the corpus callosum correlated significantly with positive psychotic symptom severity.

Conclusions

We demonstrate that the t(1;11) translocation is associated with reduced white matter integrity in frontal commissural and association fibre tracts. These findings overlap with those shown in affected patients with psychosis and in DISC1 animal models and highlight the value of rare but biologically informative mutations in modeling psychosis.

Boymaw, overexpressed in brains with major psychiatric disorders, may encode a small protein to inhibit mitochondrial function and protein translation

The t(1,11) chromosome translocation co-segregates with major psychiatric disorders in a large Scottish family. The translocation disrupts the DISC1and Boymaw (DISC1FP1) genes on chromosomes 1 and 11, respectively. After translocation, two fusion genes are generated. Our recent studies found that the DISC1-Boymaw fusion protein is localized in mitochondria and inhibits oxidoreductase activity, rRNA expression, and protein translation. Mice carrying the DISC1-Boymaw fusion genes display intermediate behavioral phenotypes related to major psychiatric disorders. Here, we report that the Boymaw gene may encode a small protein predominantly localized in mitochondria. The Boymaw protein inhibits oxidoreductase activity, rRNA expression, and protein translation in the same way as the DISC1-Boymaw fusion protein. Interestingly, Boymaw expression is up-regulated by different stressors at RNA and/or protein translational levels. In addition, we found that Boymaw RNA expression is significantly increased in the postmortem brains of patients with major psychiatric disorders. Our studies therefore suggest that the Boymaw gene could potentially be a susceptibility gene for major psychiatric disorders in both the Scottish t(1,11) family and the general population of patients.

Potential primary roles of glial cells in the mechanisms of psychiatric disorders

While neurons have long been considered the major player in multiple brain functions such as perception, emotion, and memory, glial cells have been relegated to a far lesser position, acting as merely a “glue” to support neurons. Multiple lines of recent evidence, however, have revealed that glial cells such as oligodendrocytes, astrocytes, and microglia, substantially impact on neuronal function and activities and are significantly involved in the underlying pathobiology of psychiatric disorders. Indeed, a growing body of evidence indicates that glial cells interact extensively with neurons both chemically (e.g., through neurotransmitters, neurotrophic factors, and cytokines) and physically (e.g., through gap junctions), supporting a role for these cells as likely significant modifiers not only of neural function in brain development but also disease pathobiology. Since questions have lingered as to whether glial dysfunction plays a primary role in the biology of neuropsychiatric disorders or a role related solely to their support of neuronal physiology in these diseases, informative and predictive animal models have been developed over the last decade. In this article, we review recent findings uncovered using glia-specific genetically modified mice with which we can evaluate both the causation of glia dysfunction and its potential role in neuropsychiatric disorders such as autism and schizophrenia.

Genetic Sources of Subcomponents of Event-Related Potential in the Dimension of Psychosis Analyzed From the B-SNIP Study

OBJECTIVE

Biological risk factors underlying psychosis are poorly understood. Biological underpinnings of the dimension of psychosis can be derived using genetic associations with intermediate phenotypes such as subcomponents of auditory event-related potentials (ERPs). Various ERP subcomponent abnormalities in schizophrenia and psychotic bipolar disorder are heritable and are expressed in unaffected relatives, although studies investigating genetic contributions to ERP abnormalities are limited. The authors used a novel parallel independent component analysis (para-ICA) to determine which empirically derived gene clusters are associated with data-driven ERP subcomponents, assuming a complex etiology underlying psychosis.

METHOD

The authors examined the multivariate polygenic association of ERP subcomponents from 64-channel auditory oddball data in 144 individuals with schizophrenia, 210 psychotic bipolar disorder probands, and 95 healthy individuals from the multisite Bipolar-Schizophrenia Network on Intermediate Phenotypes study. Data were reduced by principal components analysis to two target and one standard ERP waveforms. Multivariate association of compressed ERP waveforms with a set of 20,329 single-nucleotide polymorphisms (SNPs) (reduced from a 1-million-SNP array) was examined using para-ICA. Genes associated with SNPs were further examined using pathway analysis tools.

RESULTS

Para-ICA identified four ERP components that were significantly correlated with three genetic components. Enrichment analysis revealed complement immune response pathway and multiple processes that significantly mediate ERP abnormalities in psychosis, including synaptic cell adhesion, axon guidance, and neurogenesis.

CONCLUSIONS

This study identified three genetic components comprising multiple genes mediating ERP subcomponent abnormalities in schizophrenia and psychotic bipolar disorder. The data suggest a possible polygenic structure comprising genes influencing key neurodevelopmental processes, neural circuitry, and brain function mediating biological pathways plausibly associated with psychosis.

Altered functional brain network connectivity and glutamate system function in transgenic mice expressing truncated Disrupted-in-Schizophrenia 1

Considerable evidence implicates DISC1 as a susceptibility gene for multiple psychiatric diseases. DISC1 has been intensively studied at the molecular, cellular and behavioral level, but its role in regulating brain connectivity and brain network function remains unknown. Here, we utilize a set of complementary approaches to assess the functional brain network abnormalities present in mice expressing a truncated Disc1 gene (Disc1tr Hemi mice). Disc1tr Hemi mice exhibited hypometabolism in the prefrontal cortex (PFC) and reticular thalamus along with a reorganization of functional brain network connectivity that included compromised hippocampal-PFC connectivity. Altered hippocampal-PFC connectivity in Disc1tr Hemi mice was confirmed by electrophysiological analysis, with Disc1tr Hemi mice showing a reduced probability of presynaptic neurotransmitter release in the monosynaptic glutamatergic hippocampal CA1-PFC projection. Glutamate system dysfunction in Disc1tr Hemi mice was further supported by the attenuated cerebral metabolic response to the NMDA receptor (NMDAR) antagonist ketamine and decreased hippocampal expression of NMDAR subunits 2A and 2B in these animals. These data show that the Disc1 truncation in Disc1tr Hemi mice induces a range of translationally relevant endophenotypes underpinned by glutamate system dysfunction and altered brain connectivity.

A framework for analyzing the relationship between gene expression and morphological, topological, and dynamical patterns in neuronal networks

BACKGROUND

A key point in developmental biology is to understand how gene expression influences the morphological and dynamical patterns that are observed in living beings.

NEW METHOD

In this work we propose a methodology capable of addressing this problem that is based on estimating the mutual information and Pearson correlation between the intensity of gene expression and measurements of several morphological properties of the cells. A similar approach is applied in order to identify effects of gene expression over the system dynamics. Neuronal networks were artificially grown over a lattice by considering a reference model used to generate artificial neurons. The input parameters of the artificial neurons were determined according to two distinct patterns of gene expression and the dynamical response was assessed by considering the integrate-and-fire model.

RESULTS

As far as single gene dependence is concerned, we found that the interaction between the gene expression and the network topology, as well as between the former and the dynamics response, is strongly affected by the gene expression pattern. In addition, we observed a high correlation between the gene expression and some topological measurements of the neuronal network for particular patterns of gene expression.

COMPARISON WITH EXISTING METHODS

To our best understanding, there are no similar analyses to compare with.

CONCLUSIONS

A proper understanding of gene expression influence requires jointly studying the morphology, topology, and dynamics of neurons. The proposed framework represents a first step towards predicting gene expression patterns from morphology and connectivity.

Disordered ripples are a common feature of genetically distinct mouse models relevant to schizophrenia

We present results from a novel comparative approach to the study of mechanisms of psychiatric disease. Previous work examined neural activity patterns in the hippocampus of a freely behaving mouse model associated with schizophrenia, the calcineurin knockout mouse. Here we examined a genetically distinct mouse that exhibits a similar set of behavioral phenotypes associated with schizophrenia, a transgenic model expressing a putative dominant-negative DISC1 (DN-DISC1). Strikingly, the principal finding of the earlier work is replicated in the DN-DISC1 mice, that is, a selective increase in the numbers of sharp-wave ripple events in the local hippocampal LFP, while at the same time other LFP patterns such as theta and gamma are unaffected. Sharp-wave ripples are thought to arise from hippocampal circuits, and reflect the coordinated activity of the principal excitatory cells of the hippocampus, in specific patterns that represent reactivated memories of previous experiences and imagined future experiences that predict behavior. These findings suggest that multiple genetic alterations could converge on distinct patterns of aberrant neurophysiological function to give rise to common behavioral phenotypes in psychiatric disease.

Hippocampal place cell and inhibitory neuron activity in disrupted-in-schizophrenia-1 mutant mice: implications for working memory deficits

Background:

Despite the prevalence of working memory deficits in schizophrenia, the neuronal mechanisms mediating these deficits are not fully understood. Importantly, deficits in spatial working memory are identified in numerous mouse models that exhibit schizophrenia-like endophenotypes. The hippocampus is one of the major brain regions that actively encodes spatial location, possessing pyramidal neurons, commonly referred to as ‘place cells’, that fire in a location-specific manner. This study tests the hypothesis that mice with a schizophrenia-like endophenotype exhibit impaired encoding of spatial location in the hippocampus.

Aims:

To characterize hippocampal place cell activity in mice that exhibit a schizophrenia-like endophenotype.

Methods:

We recorded CA1 place cell activity in six control mice and six mice that carry a point mutation in the disrupted-in-schizophrenia-1 gene (Disc1-L100P) and have previously been shown to exhibit deficits in spatial working memory.

Results:

The spatial specificity and stability of Disc1-L100P place cells were similar to wild-type place cells. Importantly, however, Disc1-L100P place cells exhibited a higher propensity to increase their firing rate in a single, large location of the environment, rather than multiple smaller locations, indicating a generalization in their spatial selectivity. Alterations in the signaling and numbers of CA1 putative inhibitory interneurons and decreased hippocampal theta (5–12 Hz) power were also identified in the Disc1-L100P mice.

Conclusions:

The generalized spatial selectivity of Disc1-L100P place cells suggests a simplification of the ensemble place codes that encode individual locations and subserve spatial working memory. Moreover, these results suggest that deficient working memory in schizophrenia results from an impaired ability to uniquely code the individual components of a memory sequence.

Supplementary information

The online version of this article (doi:10.1038/npjschz.2015.11) contains supplementary material, which is available to authorized users.

Place cells that encode spatial information in the hippocampus in the brain have abnormal activity in a mouse model of schizophrenia. Researchers led by Lia Mesbah-Oskui at the University of Toronto, Canada, measured the activity of place cells in healthy mice and in mice that have a mutation in the Disrupted-in-schizophrenia-1 gene; this gene has previously been associated with schizophrenia, and the mutant mice exhibit similar cognitive impairments to those observed in patients with schizophrenia. Although place cells showed normal, location-specific increases in activity in mutant mice, each cell was less selective about the locations to which it responded. Consequently, the ensembles of place cells that normally encode specific locations were simpler and less unique. This impairment might underlie spatial memory deficits that are observed in people with schizophrenia.

Impaired fast-spiking interneuron function in a genetic mouse model of depression

Rhythmic neuronal activity provides a frame for information coding by co-active cell assemblies. Abnormal brain rhythms are considered as potential pathophysiological mechanisms causing mental disease, but the underlying network defects are largely unknown. We find that mice expressing truncated Disrupted-in-Schizophrenia 1 (Disc1), which mirror a high-prevalence genotype for human psychiatric illness, show depression-related behavior. Theta and low-gamma synchrony in the prelimbic cortex (PrlC) is impaired in Disc1 mice and inversely correlated with the extent of behavioural despair. While weak theta activity is driven by the hippocampus, disturbance of low-gamma oscillations is caused by local defects of parvalbumin (PV)-expressing fast-spiking interneurons (FS-INs). The number of FS-INs is reduced, they receive fewer excitatory inputs, and form fewer release sites on targets. Computational analysis indicates that weak excitatory input and inhibitory output of FS-INs may lead to impaired gamma oscillations. Our data link network defects with a gene mutation underlying depression in humans.

DOI:http://dx.doi.org/10.7554/eLife.04979.001

Our thoughts and emotions are produced and processed by complex networks of neurons inside our brains. Signals are sent from one neuron to another via chemical messengers, and pass through the neuron as an electrical signal. The electrical signals produced by a brain region often show steady rhythms, or oscillations. In the brains of many people diagnosed with certain mental disorders, such as schizophrenia and major depression, these oscillations are disrupted, but how these changes in rhythm are linked to defects in the networks of neurons behind the electrical activity is not well understood.

Studies of a family in Scotland over several decades revealed that a gene called DISC1 was shortened in family members who had been diagnosed with mental illnesses. Recently, scientists have been able to create mice that have mutations that are equivalent to this DISC1 mutation. It is hoped that studying the behavior and neural activity of these mutant mice could lead to a better understanding of human mental disorders.

Sauer et al. confirmed that the mutant mice showed depression-related behavior; in experiments that involved trying to escape from hopeless situations, the mutant mice gave up on their escape attempts much sooner than the normal mice. Recording the brain activity of these ‘depressed’ mice showed that the activity of a brain region called the prelimbic cortex was weak and disordered—very much like the brain activity seen in human depression. In particular, two types of brain activity, called theta and low-gamma oscillations, were not synchronized.

To determine precisely what causes these abnormal oscillations, Sauer et al. took brain slices from depressed mice, and then stained them with dyes that showed the circuits in the prelimbic cortex more clearly. This revealed that depressed mice had developmental defects in a specific type of inhibitory neuron called fast-spiking interneurons—there were fewer of these cells, and the neurons that were there did not have the correct number of connections to other neurons. Further investigation showed that these neurons had difficulties receiving and releasing the chemical messengers that allow neurons to communicate, and Sauer et al. thought that this might cause the low-gamma oscillation problems.

To confirm this theory, Sauer et al. created a computer model that simulated the defective interneurons. The simulations support the theory that the defects in the fast-spiking interneurons cause the abnormal low-gamma rhythms seen in depressed mice. In the future, a better understanding of the defects of inhibitory cells in DISC1 mutants and other mouse models of mental illness might open up new avenues for targeted drug design. As the prelimbic cortex combines inputs from various other brain areas, a further challenge will be to examine whether these inputs influence the activity of the prelimbic cortex and thus contribute to depression-related behavior.

DOI:http://dx.doi.org/10.7554/eLife.04979.002

DISC1 gene and affective psychopathology: a combined structural and functional MRI study

The gene Disrupted-In-Schizophrenia-1 (DISC1) has been indicated as a determinant of psychopathology, including affective disorders, and shown to influence prefrontal cortex (PFC) and hippocampus functioning, regions of major interest for affective disorders. We aimed to investigate whether DISC1 differentially modulates brain function during executive and memory processing, and morphology in regions relevant for depression and anxiety disorders (affective disorders). 128 participants, with (n = 103) and without (controls; n = 25) affective disorders underwent genotyping for Ser704Cys (with Cys-allele considered as risk-allele) and structural and functional (f) Magnetic Resonance Imaging (MRI) during visuospatial planning and emotional episodic memory tasks. For both voxel-based morphometry and fMRI analyses, we investigated the effect of genotype in controls and explored genotypeXdiagnosis interactions. Results are reported at p < 0.05 FWE small volume corrected. In controls, Cys-carriers showed smaller bilateral (para)hippocampal volumes compared with Ser-homozygotes, and lower activation in the anterior cingulate cortex (ACC) and dorsolateral PFC during visuospatial planning. In anxiety patients, Cys-carriers showed larger (para)hippocampal volumes and more ACC activation during visuospatial planning. In depressive patients, no effect of genotype was observed and overall, no effect of genotype on episodic memory processing was detected. We demonstrated that Ser704Cys-genotype influences (para)hippocampal structure and functioning the dorsal PFC during executive planning, most prominently in unaffected controls. Results suggest that presence of psychopathology moderates Ser704Cys effects.

DISC1 Ser704Cys impacts thalamic-prefrontal connectivity

The Disrupted-in-Schizophrenia 1 (DISC1) gene has been thought as a putative susceptibility gene for various psychiatric disorders, and DISC1 Ser704Cys is associated with variations of brain morphology and function. Moreover, our recent diffusion magnetic resonance imaging (dMRI) study reported that DISC1 Ser704Cys was associated with information transfer efficiency in the brain anatomical network. However, the effects of the DISC1 gene on functional brain connectivity and networks, especially for thalamic-prefrontal circuit, which are disrupted in various psychiatric disorders, are largely unknown. Using a functional connectivity density (FCD) mapping method based on functional magnetic resonance imaging data in a large sample of healthy Han Chinese subjects, we first investigated the association between DISC1 Ser704Cys and short- and long-range FCD hubs. Compared with Ser homozygotes, Cys-allele individuals had increased long-range FCD hubs in the bilateral thalami. The functional and anatomical connectivity of the thalamus to the prefrontal cortex was further analyzed. Significantly increased thalamic-prefrontal functional connectivity and decreased thalamic-prefrontal anatomical connectivity were found in DISC1 Cys-allele carriers. Our findings provide consistent evidence that the DISC1 Ser704Cys polymorphism influences the thalamic-prefrontal circuits in humans and may provide new insights into the neural mechanisms that link DISC1 and the risk for psychiatric disorders.

RNA Sequencing in Schizophrenia

Schizophrenia (SCZ) is a serious psychiatric disorder that affects 1% of general population and places a heavy burden worldwide. The underlying genetic mechanism of SCZ remains unknown, but studies indicate that the disease is associated with a global gene expression disturbance across many genes. Next-generation sequencing, particularly of RNA sequencing (RNA-Seq), provides a powerful genome-scale technology to investigate the pathological processes of SCZ. RNA-Seq has been used to analyze the gene expressions and identify the novel splice isoforms and rare transcripts associated with SCZ. This paper provides an overview on the genetics of SCZ, the advantages of RNA-Seq for transcriptome analysis, the accomplishments of RNA-Seq in SCZ cohorts, and the applications of induced pluripotent stem cells and RNA-Seq in SCZ research.

Disrupted in schizophrenia 1 and synaptic function in the mammalian central nervous system

The disrupted in schizophrenia 1 (DISC1) gene is found at the breakpoint of an inherited chromosomal translocation, and segregates with major mental illnesses. Its potential role in central nervous system (CNS) malfunction has triggered intensive investigation of the biological roles played by DISC1, with the hope that this may shed new light on the pathobiology of psychiatric disease. Such work has ranged from investigations of animal behavior to detailed molecular-level analysis of the assemblies that DISC1 forms with other proteins. Here, we discuss the evidence for a role of DISC1 in synaptic function in the mammalian CNS.

Neurophysiological modification of CA1 pyramidal neurons in a transgenic mouse expressing a truncated form of disrupted-in-schizophrenia 1

A t(1;11) balanced chromosomal translocation transects the Disc1 gene in a large Scottish family and produces genome-wide linkage to schizophrenia and recurrent major depressive disorder. This study describes our in vitro investigations into neurophysiological function in hippocampal area CA1 of a transgenic mouse (DISC1_tr) that expresses a truncated version of DISC1 designed to reproduce aspects of the genetic situation in the Scottish t(1;11) pedigree. We employed both patch-clamp and extracellular recording methods in vitro to compare intrinsic properties and synaptic function and plasticity between DISC1_tr animals and wild-type littermates. Patch-clamp analysis of CA1 pyramidal neurons (CA1-PNs) revealed no genotype dependence in multiple subthreshold parameters, including resting potential, input resistance, hyperpolarization-activated ‘sag’ and resonance properties. Suprathreshold stimuli revealed no alteration to action potential (AP) waveform, although the initial rate of AP production was higher in DISC1_tr mice. No difference was observed in afterhyperpolarizing potentials following trains of 5–25 APs at 50 Hz. Patch-clamp analysis of synaptic responses in the Schaffer collateral commissural (SC) pathway indicated no genotype-dependence of paired pulse facilitation, excitatory postsynaptic potential summation or AMPA/NMDA ratio. Extracellular recordings also revealed an absence of changes to SC synaptic responses and indicated input–output and short-term plasticity were also unaltered in the temporoammonic (TA) input. However, in DISC1_tr mice theta burst-induced long-term potentiation was enhanced in the SC pathway but completely lost in the TA pathway. These data demonstrate that expressing a truncated form of DISC1 affects intrinsic properties of CA1-PNs and produces pathway-specific effects on long-term synaptic plasticity.

The study of psychiatric disease genes and drugs in zebrafish

Mutations associated with psychiatric disease are being identified, but it remains unclear how the affected genes contribute to disease. Zebrafish is an emerging model to study psychiatric disease genes with a rich repertoire of phenotyping tools. Recent zebrafish research has uncovered potential developmental phenotypes for genes associated with psychiatric disorders, while drug screens have behaviorally characterized small molecules and identified new classes of drugs. Behavioral studies have led to promising models for endophenotypes of psychiatric diseases. While further research is needed to firmly link these models to psychiatric disorders, they are valuable tools for phenotyping genetic mutations and drugs. Recently developed tools in genome editing and in vivo imaging promise additional insights into the processes disrupted by mutations in psychiatric disease genes.

Risk-associated coding synonymous SNPs in type 2 diabetes and neurodegenerative diseases: genetic silence and the underrated association with splicing regulation and epigenetics

Single nucleotide polymorphisms (SNPs) are tentatively critical with regard to disease predisposition, but coding synonymous SNPs (sSNPs) are generally considered "neutral". Nevertheless, sSNPs in serine/arginine-rich (SR) and splice-site (SS) exonic splicing enhancers (ESEs) or in exonic CpG methylation targets, could be decisive for splicing, particularly in aging-related conditions, where mis-splicing is frequently observed. We presently identified 33 genes T2D-related and 28 related to neurodegenerative diseases, by investigating the impact of the corresponding coding sSNPs on splicing and using gene ontology data and computational tools. Potentially critical (prominent) sSNPs comply with the following criteria: changing the splicing potential of prominent SR-ESEs or of significant SS-ESEs by >1.5 units (Δscore), or formation/deletion of ESEs with maximum splicing score. We also noted the formation/disruption of CpGs (tentative methylation sites of epigenetic sSNPs). All disease association studies involving sSNPs are also reported. Only 21/670 coding SNPs, mostly epigenetic, reported in 33 T2D-related genes, were found to be prominent coding synonymous. No prominent sSNPs have been recorded in three key T2D-related genes (GCGR, PPARGC1A, IGF1). Similarly, 20/366 coding synonymous were identified in ND related genes, mostly epigenetic. Meta-analysis showed that 17 of the above prominent sSNPs were previously investigated in association with various pathological conditions. Three out of four sSNPs (all epigenetic) were associated with T2D and one with NDs (branch site sSNP). Five were associated with other or related pathological conditions. None of the four sSNPs introducing new ESEs was found to be disease-associated. sSNPs introducing smaller Δscore changes (<1.5) in key proteins (INSR, IRS1, DISC1) were also correlated to pathological conditions. This data reveals that genetic variation in splicing-regulatory and particularly CpG sites might be related to disease predisposition and that in-silico analysis is useful for identifying sSNPs, which might be falsely identified as silent or synonymous.

Synaptic plasticity, neural circuits, and the emerging role of altered short-term information processing in schizophrenia

Synaptic plasticity alters the strength of information flow between presynaptic and postsynaptic neurons and thus modifies the likelihood that action potentials in a presynaptic neuron will lead to an action potential in a postsynaptic neuron. As such, synaptic plasticity and pathological changes in synaptic plasticity impact the synaptic computation which controls the information flow through the neural microcircuits responsible for the complex information processing necessary to drive adaptive behaviors. As current theories of neuropsychiatric disease suggest that distinct dysfunctions in neural circuit performance may critically underlie the unique symptoms of these diseases, pathological alterations in synaptic plasticity mechanisms may be fundamental to the disease process. Here we consider mechanisms of both short-term and long-term plasticity of synaptic transmission and their possible roles in information processing by neural microcircuits in both health and disease. As paradigms of neuropsychiatric diseases with strongly implicated risk genes, we discuss the findings in schizophrenia and autism and consider the alterations in synaptic plasticity and network function observed in both human studies and genetic mouse models of these diseases. Together these studies have begun to point toward a likely dominant role of short-term synaptic plasticity alterations in schizophrenia while dysfunction in autism spectrum disorders (ASDs) may be due to a combination of both short-term and long-term synaptic plasticity alterations.

Neuropeptide precursor VGF is genetically associated with social anhedonia and underrepresented in the brain of major mental illness: its downregulation by DISC1

In a large Scottish pedigree, disruption of the gene coding for DISC1 clearly segregates with major depression, schizophrenia and related mental conditions. Thus, study of DISC1 may provide a clue to understand the biology of major mental illness. A neuropeptide precursor VGF has potent antidepressant effects and has been reportedly associated with bipolar disorder. Here we show that DISC1 knockdown leads to a reduction of VGF, in neurons. VGF is also downregulated in the cortices from sporadic cases with major mental disease. A positive correlation of VGF single-nucleotide polymorphisms (SNPs) with social anhedonia was also observed. We now propose that VGF participates in a common pathophysiology of major mental disease.

Genetics of schizophrenia

The genetic basis of schizophrenia has been a hotly debated research topic for decades, yet recent studies, especially in the past year, have confirmed genetics as the major cause of this complex condition. Psychiatry has come of age: it is perhaps more difficult for the current generation of psychiatrists, to comprehend how the biological root of the condition could have been denied for so long. Here we review how highly collaborative global efforts to pool samples, utilise the very latest advances in genotyping and high throughput sequencing technologies, and application of robust statistical analysis have reaped phenomenal rewards. The major findings are that schizophrenia is a highly polygenic disorder with a complex array of risk loci, many include genes implicated also in intellectual disability, autism spectrum disorders, bipolar disorder and major depressive disorder. These candidate genes converge on key neuronal signalling pathways identifying novel targets for potential future therapeutic intervention.

Systematic prioritization and integrative analysis of copy number variations in schizophrenia reveal key schizophrenia susceptibility genes

Schizophrenia is a common mental disorder with high heritability and strong genetic heterogeneity. Common disease-common variants hypothesis predicts that schizophrenia is attributable in part to common genetic variants. However, recent studies have clearly demonstrated that copy number variations (CNVs) also play pivotal roles in schizophrenia susceptibility and explain a proportion of missing heritability. Though numerous CNVs have been identified, many of the regions affected by CNVs show poor overlapping among different studies, and it is not known whether the genes disrupted by CNVs contribute to the risk of schizophrenia. By using cumulative scoring, we systematically prioritized the genes affected by CNVs in schizophrenia. We identified 8 top genes that are frequently disrupted by CNVs, including NRXN1, CHRNA7, BCL9, CYFIP1, GJA8, NDE1, SNAP29, and GJA5. Integration of genes affected by CNVs with known schizophrenia susceptibility genes (from previous genetic linkage and association studies) reveals that many genes disrupted by CNVs are also associated with schizophrenia. Further protein-protein interaction (PPI) analysis indicates that protein products of genes affected by CNVs frequently interact with known schizophrenia-associated proteins. Finally, systematic integration of CNVs prioritization data with genetic association and PPI data identifies key schizophrenia candidate genes. Our results provide a global overview of genes impacted by CNVs in schizophrenia and reveal a densely interconnected molecular network of de novo CNVs in schizophrenia. Though the prioritized top genes represent promising schizophrenia risk genes, further work with different prioritization methods and independent samples is needed to confirm these findings. Nevertheless, the identified key candidate genes may have important roles in the pathogenesis of schizophrenia, and further functional characterization of these genes may provide pivotal targets for future therapeutics and diagnostics.

No evidence of DISC1-associated morphological changes in the hippocampus, anterior cingulate cortex, or striatum in major depressive disorder cases and healthy controls

BACKGROUND

DISC1 imaging genetics studies in healthy controls, schizophrenia, and bipolar disorder cases have revealed morphological changes in brain regions involved in the pathophysiology of psychiatric disease including the hippocampus, anterior cingulate cortex (ACC), and the striatum. However, many of these studies have yielded discordant findings so there is a need for replication. Furthermore, despite evidence from human genetic studies and animal models implicating DISC1 in major depressive disorder (MDD), a DISC1 imaging genetics study in MDD cases has yet to be published. Thus, using neuroimaging data from MDD cases and a large sample of healthy controls we aimed to identify morphological changes representing neurobiological mechanisms underlying the association between DISC1 and MDD.

METHODS

We utilized structural magnetic resonance imaging (sMRI) data from 512 healthy controls and 171 current MDD (SCID interview) cases, each with genotype data for non-synonymous DISC1 SNPs rs3738401, rs6675281, and rs821616.

RESULTS

Region of interest analyses failed to reveal DISC1-associated morphological changes in the hippocampus, ACC, or striatum in MDD patients and healthy controls. Whole brain exploratory analyses identified a nominally significant cluster mapping to the border of the precentral and postcentral gyri associated with rs821616 in healthy controls only (p(uncorrected)<0.001).

LIMITATIONS

We focused our analyses exclusively on three, but previously heavily studied, SNPs in DISC1.

CONCLUSIONS

Our findings suggest that morphological changes in the hippocampus, ACC, and/or striatum of MDD patients do not represent neurobiological mechanisms underlying the association between DISC1 and MDD. However, we urge replication in independent samples of MDD cases.

Hippocampal granule cell pathology in epilepsy - a possible structural basis for comorbidities of epilepsy?

Temporal lobe epilepsy in both animals and humans is characterized by abnormally integrated hippocampal dentate granule cells. Among other abnormalities, these cells make axonal connections with inappropriate targets, grow dendrites in the wrong direction, and migrate to ectopic locations. These changes promote the formation of recurrent excitatory circuits, leading to the appealing hypothesis that these abnormal cells may by epileptogenic. While this hypothesis has been the subject of intense study, less attention has been paid to the possibility that abnormal granule cells in the epileptic brain may also contribute to comorbidities associated with the disease. Epilepsy is associated with a variety of general findings, such as memory disturbances and cognitive dysfunction, and is often comorbid with a number of other conditions, including schizophrenia and autism. Interestingly, recent studies implicate disruption of common genes and gene pathways in all three diseases. Moreover, while neuropsychiatric conditions are associated with changes in a variety of brain regions, granule cell abnormalities in temporal lobe epilepsy appear to be phenocopies of granule cell deficits produced by genetic mouse models of autism and schizophrenia, suggesting that granule cell dysmorphogenesis may be a common factor uniting these seemingly diverse diseases. Disruption of common signaling pathways regulating granule cell neurogenesis may begin to provide mechanistic insight into the cooccurrence of temporal lobe epilepsy and cognitive and behavioral disorders.

Mice with a naturally occurring DISC1 mutation display a broad spectrum of behaviors associated to psychiatric disorders

Disrupted in schizophrenia-1 (DISC1) gene is associated with several neuropsychiatric disorders as it is disrupted by a balanced translocation involving chromosomes 1 and 11 in a large Scottish pedigree with high prevalence of schizophrenia, bipolar disorder and major depression. Since its identification, several mouse models with DISC1 genetic modifications have been generated using different approaches. Interestingly, a natural deletion of 25bp in the 129 mouse strain alters the DISC1 gene reading frame leading to a premature stop codon very close to the gene breakpoint in the mutant allele of the Scottish family. In the present study we confirmed that the 129DISC1^Del mutation results in reduced level of full length DISC1 in hippocampus of heterozygous mice and we have characterized the behavioral consequences of heterozygous 129DISC1^Del mutation in a mixed B6129 genetic background. We found alterations in spontaneous locomotor activity (hyperactivity in males and hypoactivity in females), deficits in pre-pulse inhibition (PPI) and also increased despair behavior in heterozygous 129DISC1^Del mice, thus reproducing typical behaviors associated to psychiatric disorders. Since this mouse strain is widely and commercially available, we propose it as an amenable tool to study DISC1-related biochemical alterations and psychiatric behaviors.

Targeting mitochondrially mediated plasticity to develop improved therapeutics for bipolar disorder

INTRODUCTION

Bipolar disorder (BPD) is a severe illness with few treatments available. Understanding BPD pathophysiology and identifying potential relevant targets could prove useful for developing new treatments. Remarkably, subtle impairments of mitochondrial function may play an important role in BPD pathophysiology.

AREAS COVERED

This article focuses on human studies and reviews evidence of mitochondrial dysfunction in BPD as a promising target for the development of new, improved treatments. Mitochondria are crucial for energy production, generated mainly through the electron transport chain (ETC) and play an important role in regulating apoptosis and calcium (Ca²⁺) signaling as well as synaptic plasticity. Mitochondria move throughout the neurons to provide energy for intracellular signaling. Studies showed polymorphisms of mitochondria-related genes as risk factors for BPD. Postmortem studies in BPD also show decreased ETC activity/expression and increased nitrosative and oxidative stress (OxS) in patient brains. BPD has been also associated with increased OxS, Ca²⁺ dysregulation and increased proapoptotic signaling in peripheral blood. Neuroimaging studies consistently show decreased energy levels and pH in brains of BPD patients.

EXPERT OPINION

Targeting mitochondrial function, and their role in energy metabolism, synaptic plasticity and cell survival, may be an important avenue for development of new mood-stabilizing agents.

Disrupted-In-Schizophrenia-1 (DISC1) interactome and mental disorders: impact of mouse models

Disrupted-In-Schizophrenia-1 (DISC1) has captured much attention because it predisposes individuals to a wide range of mental illnesses. Notably, a number of genes encoding proteins interacting with DISC1 are also considered to be relevant risk factors of mental disorders. We reasoned that the understanding of DISC1-associated mental disorders in the context of network principles will help to address fundamental properties of DISC1 as a disease gene. Systematic integration of behavioural phenotypes of genetic mouse lines carrying perturbation in DISC1 interacting proteins would contribute to a better resolution of neurobiological mechanisms of mental disorders associated with the impaired DISC1 interactome and lead to a development of network medicine. This review also makes specific recommendations of how to assess DISC1 associated mental disorders in mouse models and discuss future directions.

Can we safely target the WNT pathway?

WNT-β-catenin signalling is involved in a multitude of developmental processes and the maintenance of adult tissue homeostasis by regulating cell proliferation, differentiation, migration, genetic stability and apoptosis, as well as by maintaining adult stem cells in a pluripotent state. Not surprisingly, aberrant regulation of this pathway is therefore associated with a variety of diseases, including cancer, fibrosis and neurodegeneration. Despite this knowledge, therapeutic agents specifically targeting the WNT pathway have only recently entered clinical trials and none has yet been approved. This Review examines the problems and potential solutions to this vexing situation and attempts to bring them into perspective.

Alterations of GABAergic and dopaminergic systems in mutant mice with disruption of exons 2 and 3 of the Disc1 gene

Disrupted-in-schizophrenia-1 (DISC1) has been widely associated with several psychiatric disorders, including schizophrenia, mood disorders and autism. We previously reported that a deficiency of DISC1 may induce low anxiety and/or high impulsivity in mice with disruption of exons 2 and 3 of the Disc1 gene (Disc1(Δ2-3/Δ2-3)). It remains unclear, however, if deficiency of DISC1 leads to specific alterations in distinct neuronal systems. In the present study, to understand the role of DISC1 in γ-aminobutyric acid (GABA) interneurons and mesocorticolimbic dopaminergic (DAergic) neurons, we investigated the number of parvalbumin (PV)-positive interneurons, methamphetamine (METH)-induced DA release and the expression levels of GABAA, DA transporter (DAT) and DA receptors in wild-type (Disc1(+/+)) and Disc1(Δ2-3/Δ2-3) mice. Female Disc1(Δ2-3/Δ2-3) mice showed a significant reduction of PV-positive interneurons in the hippocampus, while no apparent changes were observed in mRNA expression levels of GABAA receptor subunits. METH-induced DA release was significantly potentiated in the nucleus accumbens (NAc) of female Disc1(Δ2-3/Δ2-3) mice, although there were no significant differences in the expression levels of DAT. Furthermore, the expression levels of DA receptor mRNA were upregulated in the NAc of female Disc1(Δ2-3/Δ2-3) mice. Male Disc1(Δ2-3/Δ2-3) mice showed no apparent differences in all experiments. DISC1 may play a critical role in gender-specific developmental alteration in GABAergic inhibitory interneurons and DAergic neurons.

Inhibition of protein translation by the DISC1-Boymaw fusion gene from a Scottish family with major psychiatric disorders

The t(1; 11) translocation appears to be the causal genetic lesion with 70% penetrance for schizophrenia, major depression and other psychiatric disorders in a Scottish family. Molecular studies identified the disruption of the disrupted-in-schizophrenia 1 (DISC1) gene by chromosome translocation at chromosome 1q42. Our previous studies, however, revealed that the translocation also disrupted another gene, Boymaw (also termed DISC1FP1), on chromosome 11. After translocation, two fusion genes [the DISC1-Boymaw (DB7) and the Boymaw-DISC1 (BD13)] are generated between the DISC1 and Boymaw genes. In the present study, we report that expression of the DB7 fusion gene inhibits both intracellular NADH oxidoreductase activities and protein translation. We generated humanized DISC1-Boymaw mice with gene targeting to examine the in vivo functions of the fusion genes. Consistent with the in vitro studies on the DB7 fusion gene, protein translation activity is decreased in the hippocampus and in cultured primary neurons from the brains of the humanized mice. Expression of Gad67, Nmdar1 and Psd95 proteins are also reduced. The humanized mice display prolonged and increased responses to the NMDA receptor antagonist, ketamine, on various mouse genetic backgrounds. Abnormal information processing of acoustic startle and depressive-like behaviors are also observed. In addition, the humanized mice display abnormal erythropoiesis, which was reported to associate with depression in humans. Expression of the DB7 fusion gene may reduce protein translation to impair brain functions and thereby contribute to the pathogenesis of major psychiatric disorders.

708 Common and 2010 rare DISC1 locus variants identified in 1542 subjects: analysis for association with psychiatric disorder and cognitive traits

A balanced t(1;11) translocation that transects the Disrupted in schizophrenia 1 (DISC1) gene shows genome-wide significant linkage for schizophrenia and recurrent major depressive disorder (rMDD) in a single large Scottish family, but genome-wide and exome sequencing-based association studies have not supported a role for DISC1 in psychiatric illness. To explore DISC1 in more detail, we sequenced 528 kb of the DISC1 locus in 653 cases and 889 controls. We report 2718 validated single-nucleotide polymorphisms (SNPs) of which 2010 have a minor allele frequency of <1%. Only 38% of these variants are reported in the 1000 Genomes Project European subset. This suggests that many DISC1 SNPs remain undiscovered and are essentially private. Rare coding variants identified exclusively in patients were found in likely functional protein domains. Significant region-wide association was observed between rs16856199 and rMDD (P=0.026, unadjusted P=6.3 × 10(-5), OR=3.48). This was not replicated in additional recurrent major depression samples (replication P=0.11). Combined analysis of both the original and replication set supported the original association (P=0.0058, OR=1.46). Evidence for segregation of this variant with disease in families was limited to those of rMDD individuals referred from primary care. Burden analysis for coding and non-coding variants gave nominal associations with diagnosis and measures of mood and cognition. Together, these observations are likely to generalise to other candidate genes for major mental illness and may thus provide guidelines for the design of future studies.