Subcellular targeting of DISC1 is dependent on a domain independent from the Nudel binding site

Aggregation of Disrupted in Schizophrenia 1 arises from a central region of the protein

An emerging approach to studying major mental illness is through proteostasis, with the identification of several proteins that form insoluble aggregates in the brains of patients. One of these is Disrupted in Schizophrenia 1 (DISC1), a neurodevelopmentally-important scaffold protein, and product of a classic schizophrenia risk gene. DISC1 aggregates have been detected in post mortem brain tissue from patients with schizophrenia, bipolar disorder and major depressive disorder, as well as various model systems, although the mechanism by which it aggregates is still unclear. Aggregation of two other proteins implicated in mental illness, TRIOBP-1 and NPAS3, was shown to be dependent on very specific structural regions of the protein. We therefore looked at the domain structure of DISC1, and investigated which structural elements are key for its aggregation. While none of the known structured DISC1 regions (named D, I, S and C respectively) formed aggregates individually when expressed in neuroblastoma cells, the combination of the D and I regions, plus the linker region between them, formed visible aggregates. Further refinement revealed that a region of approximately 30 amino acids between these two regions is critical for aggregation, and deletion of this region is sufficient to abolish the aggregation propensity of DISC1. This finding from mammalian cell culture contrasts with the recent determination that the C-region of DISC1 can aggregate in vitro, although some variations of the C-terminal of DISC1 could aggregate in our system. It therefore appears likely that DISC1 aggregation, implicated in mental illness, can occur through at least two distinct mechanisms.

Dysregulated Signaling at Postsynaptic Density: A Systematic Review and Translational Appraisal for the Pathophysiology, Clinics, and Antipsychotics' Treatment of Schizophrenia

Emerging evidence from genomics, post-mortem, and preclinical studies point to a potential dysregulation of molecular signaling at postsynaptic density (PSD) in schizophrenia pathophysiology. The PSD that identifies the archetypal asymmetric synapse is a structure of approximately 300 nm in diameter, localized behind the neuronal membrane in the glutamatergic synapse, and constituted by more than 1000 proteins, including receptors, adaptors, kinases, and scaffold proteins. Furthermore, using FASS (fluorescence-activated synaptosome sorting) techniques, glutamatergic synaptosomes were isolated at around 70 nm, where the receptors anchored to the PSD proteins can diffuse laterally along the PSD and were stabilized by scaffold proteins in nanodomains of 50-80 nm at a distance of 20-40 nm creating "nanocolumns" within the synaptic button. In this context, PSD was envisioned as a multimodal hub integrating multiple signaling-related intracellular functions. Dysfunctions of glutamate signaling have been postulated in schizophrenia, starting from the glutamate receptor's interaction with scaffolding proteins involved in the N-methyl-D-aspartate receptor (NMDAR). Despite the emerging role of PSD proteins in behavioral disorders, there is currently no systematic review that integrates preclinical and clinical findings addressing dysregulated PSD signaling and translational implications for antipsychotic treatment in the aberrant postsynaptic function context. Here we reviewed a critical appraisal of the role of dysregulated PSD proteins signaling in the pathophysiology of schizophrenia, discussing how antipsychotics may affect PSD structures and synaptic plasticity in brain regions relevant to psychosis.

Mutations in DISC1 alter IP3R and voltage-gated Ca2+ channel functioning, implications for major mental illness

Disrupted in Schizophrenia 1 (DISC1) participates in a wide variety of developmental processes of central neurons. It also serves critical roles that underlie cognitive functioning in adult central neurons. Here we summarize DISC1’s general properties and discuss its use as a model system for understanding major mental illnesses (MMIs). We then discuss the cellular actions of DISC1 that involve or regulate Ca²⁺ signaling in adult central neurons. In particular, we focus on the tethering role DISC1 plays in transporting RNA particles containing Ca²⁺ channel subunit RNAs, including IP3R1, CACNA1C and CACNA2D1, and in transporting mitochondria into dendritic and axonal processes. We also review DISC1’s role in modulating IP₃R1 activity within mitochondria-associated ER membrane (MAM). Finally, we discuss DISC1-glycogen synthase kinase 3β (GSK3β) signaling that regulates functional expression of voltage-gated Ca²⁺ channels (VGCCs) at central synapses. In each case, DISC1 regulates the movement of molecules that impact Ca²⁺ signaling in neurons.

Estradiol reverses excitatory synapse loss in a cellular model of neuropsychiatric disorders

Loss of glutamatergic synapses is thought to be a key cellular pathology associated with neuropsychiatric disorders including schizophrenia (SCZ) and major depressive disorder (MDD). Genetic and cellular studies of SCZ and MDD using in vivo and in vitro systems have supported a key role for dysfunction of excitatory synapses in the pathophysiology of these disorders. Recent clinical studies have demonstrated that the estrogen, 17β-estradiol can ameliorate many of the symptoms experienced by patients. Yet, to date, our understanding of how 17β-estradiol exerted these beneficial effects is limited. In this study, we have tested the hypothesis that 17β-estradiol can restore dendritic spine number in a cellular model that recapitulates the loss of synapses associated with SCZ and MDD. Ectopic expression of wildtype, mutant or shRNA-mediated knockdown of Disrupted in Schizophrenia 1 (DISC1) reduced dendritic spine density in primary cortical neurons. Acute or chronic treatment with 17β-estradiol increased spine density to control levels in neurons with altered DISC1 levels. In addition, 17β-estradiol reduced the extent to which ectopic wildtype and mutant DISC1 aggregated. Furthermore, 17β-estradiol also caused the enrichment of synaptic proteins at synapses and increased the number of dendritic spines containing PSD-95 or that overlapped with the pre-synaptic marker bassoon. Taken together, our data indicates that estrogens can restore lost excitatory synapses caused by altered DISC1 expression, potentially through the trafficking of DISC1 and its interacting partners. These data highlight the possibility that estrogens exert their beneficial effects in SCZ and MDD in part by modulating dendritic spine number.

Protein misassembly and aggregation as potential convergence points for non-genetic causes of chronic mental illness

Chronic mental illnesses (CMI), such as schizophrenia or recurrent affective disorders, are complex conditions with both genetic and non-genetic elements. In many other chronic brain conditions, including Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis and frontotemporal dementia, sporadic instances of the disease are more common than gene-driven familial cases. Yet, the pathology of these conditions can be characterized by the presence of aberrant protein homeostasis, proteostasis, resulting in misfolded or aggregated proteins in the brains of patients that predominantly do not derive from genetic mutations. While visible deposits of aggregated protein have not yet been detected in CMI patients, we propose the existence of more subtle protein misassembly in these conditions, which form a continuum with the psychiatric phenotypes found in the early stages of many neurodegenerative conditions. Such proteinopathies need not rely on genetic variation. In a similar manner to the established aberrant neurotransmitter homeostasis in CMI, aberrant homeostasis of proteins is a functional statement that can only partially be explained by, but is certainly complementary to, genetic approaches. Here, we review evidence for aberrant proteostasis signatures from post mortem human cases, in vivo animal work, and in vitro analysis of candidate proteins misassembled in CMI. The five best-characterized proteins in this respect are currently DISC1, dysbindin-1, CRMP1, TRIOBP-1, and NPAS3. Misassembly of these proteins with inherently unstructured domains is triggered by extracellular stressors and thus provides a converging point for non-genetic causes of CMI.

Endogenous Cell Type-Specific Disrupted in Schizophrenia 1 Interactomes Reveal Protein Networks Associated With Neurodevelopmental Disorders

BACKGROUND

Disrupted in schizophrenia 1 (DISC1) has been implicated in a number of psychiatric diseases along with neurodevelopmental phenotypes such as the proliferation and differentiation of neural progenitor cells. While there has been significant effort directed toward understanding the function of DISC1 through the determination of its protein-protein interactions within an in vitro setting, endogenous interactions involving DISC1 within a cell type-specific setting relevant to neural development remain unclear.

METHODS

Using CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9) genome engineering technology, we inserted an endogenous 3X-FLAG tag at the C-terminus of the canonical DISC1 gene in human induced pluripotent stem cells (iPSCs). We further differentiated these cells and used affinity purification to determine protein-protein interactions involving DISC1 in iPSC-derived neural progenitor cells and astrocytes.

RESULTS

We were able to determine 151 novel cell type-specific proteins present in DISC1 endogenous interactomes. The DISC1 interactomes can be clustered into several subcomplexes that suggest novel DISC1 cell-specific functions. In addition, the DISC1 interactome in iPSC-derived neural progenitor cells associates in a connected network containing proteins found to harbor de novo mutations in patients affected by schizophrenia and contains a subset of novel interactions that are known to harbor syndromic mutations in neurodevelopmental disorders.

CONCLUSIONS

Endogenous DISC1 interactomes within iPSC-derived human neural progenitor cells and astrocytes are able to provide context to DISC1 function in a cell type-specific setting relevant to neural development and enables the integration of psychiatric disease risk factors within a set of defined molecular functions.

Mechanisms underlying the role of DISC1 in synaptic plasticity

Disrupted in schizophrenia 1 (DISC1) is an important hub protein, forming multimeric complexes by self-association and interacting with a large number of synaptic and cytoskeletal molecules. The synaptic location of DISC1 in the adult brain suggests a role in synaptic plasticity, and indeed, a number of studies have discovered synaptic plasticity impairments in a variety of different DISC1 mutants. This review explores the possibility that DISC1 is an important molecule for organizing proteins involved in synaptic plasticity and examines why mutations in DISC1 impair plasticity. It concentrates on DISC1's role in interacting with synaptic proteins, controlling dendritic structure and cellular trafficking of mRNA, synaptic vesicles and mitochondria. N-terminal directed mutations appear to impair synaptic plasticity through interactions with phosphodiesterase 4B (PDE4B) and hence protein kinase A (PKA)/GluA1 and PKA/cAMP response element-binding protein (CREB) signalling pathways, and affect spine structure through interactions with kalirin 7 (Kal-7) and Rac1. C-terminal directed mutations also impair plasticity possibly through altered interactions with lissencephaly protein 1 (LIS1) and nuclear distribution protein nudE-like 1 (NDEL1), thereby affecting developmental processes such as dendritic structure and spine maturation. Many of the same molecules involved in DISC1's cytoskeletal interactions are also involved in intracellular trafficking, raising the possibility that impairments in intracellular trafficking affect cytoskeletal development and vice versa. While the multiplicity of DISC1 protein interactions makes it difficult to pinpoint a single causal signalling pathway, we suggest that the immediate-term effects of N-terminal influences on GluA1, Rac1 and CREB, coupled with the developmental effects of C-terminal influences on trafficking and the cytoskeleton make up the two main branches of DISC1's effect on synaptic plasticity and dendritic spine stability.

Disrupted in schizophrenia 1 (DISC1) inhibits glioblastoma development by regulating mitochondria dynamics

Glioblastoma(GBM) is one of the most common and aggressive malignant primary tumors of the central nervous system and mitochondria have been proposed to participate in GBM tumorigenesis. Previous studies have identified a potential role of Disrupted in Schizophrenia 1 (DISC1), a multi-compartmentalized protein, in mitochondria. But whether DISC1 could regulate GBM tumorigenesis via mitochondria is still unknown. We determined the expression level of DISC1 by both bioinformatics analysis and tissue analysis, and found that DISC1 was highly expressed in GBM. Knocking down of DISC1 by shRNA in GBM cells significantly inhibited cell proliferation both in vitro and in vivo. In addition, down-regulation of DISC1 decreased cell migration and invasion of GBM and self renewal capacity of glioblastoma stem-like cells. Furthermore, multiple independent rings or spheres could be observed in mitochondria in GBM depleted of DISC1, while normal filamentous morphology was observed in control cells, demonstrating that DISC1 affected the mitochondrial dynamic. Dynamin-related protein 1 (Drp1) was reported to contribute to mitochondrial dynamic regulation and influence glioma cells proliferation and invasion by RHOA/ ROCK1 pathway. Our data showed a significant decrease of Drp1 both in mRNA and protein level in GBM lack of DISC1, indicating that DISC1 maybe affect the mitochondrial dynamic by regulating Drp1. Taken together, our findings reveal that DISC1 affects glioblastoma cell development via mitochondria dynamics partly by down regulation of Drp1.

Mitochondrial roles of the psychiatric disease risk factor DISC1

Ion transport during neuronal signalling utilizes the majority of the brain's energy supply. Mitochondria are key sites for energy provision through ATP synthesis and play other important roles including calcium buffering. Thus, tightly regulated distribution and function of these organelles throughout the intricate architecture of the neuron is essential for normal synaptic communication. Therefore, delineating mechanisms coordinating mitochondrial transport and function is essential for understanding nervous system physiology and pathology. While aberrant mitochondrial transport and dynamics have long been associated with neurodegenerative disease, they have also more recently been linked to major mental illness including schizophrenia, autism and depression. However, the underlying mechanisms have yet to be elucidated, due to an incomplete understanding of the combinations of genetic and environmental factors contributing to these conditions. Consequently, the DISC1 gene has undergone intense study since its discovery at the site of a balanced chromosomal translocation, segregating with mental illness in a Scottish pedigree. The precise molecular functions of DISC1 remain elusive. Reported functions of DISC1 include regulation of intracellular signalling pathways, neuronal migration and dendritic development. Intriguingly, a role for DISC1 in mitochondrial homeostasis and transport is fast emerging. Therefore, a major function of DISC1 in regulating mitochondrial distribution, ATP synthesis and calcium buffering may be disrupted in psychiatric disease. In this review, we discuss the links between DISC1 and mitochondria, considering both trafficking of these organelles and their function, and how, via these processes, DISC1 may contribute to the regulation of neuronal behavior in normal and psychiatric disease states.

An unpredicted aggregation-critical region of the actin-polymerizing protein TRIOBP-1/Tara, determined by elucidation of its domain structure

Aggregation of specific proteins in the brains of patients with chronic mental illness as a result of disruptions in proteostasis is an emerging theme in the study of schizophrenia in particular. Proteins including DISC1 (disrupted in schizophrenia 1) and dysbindin-1B are found in insoluble forms within brain homogenates from such patients. We recently identified TRIOBP-1 (Trio-binding protein 1, also known as Tara) to be another such protein through an epitope discovery and proteomics approach by comparing post-mortem brain material from schizophrenia patients and control individuals. We hypothesized that this was likely to occur as a result of a specific subcellular process and that it, therefore, should be possible to identify a region of the TRIOBP-1 protein that is essential for its aggregation to occur. Here, we probe the domain organization of TRIOBP-1, finding it to possess two distinct coiled-coil domains: the central and C-terminal domains. The central domain inhibits the depolymerization of F-actin and is also responsible for oligomerization of TRIOBP-1. Along with an N-terminal pleckstrin homology domain, the central domain affects neurite outgrowth. In neuroblastoma cells it was found that the aggregation propensity of TRIOBP-1 arises from its central domain, with a short "linker" region narrowed to within amino acids 324-348, between its first two coiled coils, as essential for the formation of TRIOBP-1 aggregates. TRIOBP-1 aggregation, therefore, appears to occur through one or more specific cellular mechanisms, which therefore have the potential to be of physiological relevance for the biological process underlying the development of chronic mental illness.

DISC1 causes associative memory and neurodevelopmental defects in fruit flies

Originally found in a Scottish family with diverse mental disorders, the DISC1 protein has been characterized as an intracellular scaffold protein that associates with diverse binding partners in neural development. To explore its functions in a genetically tractable system, we expressed the human DISC1 in fruit flies (Drosophila melanogaster). As in mammalian neurons, DISC1 is localized to diverse subcellular domains of developing fly neurons including the nuclei, axons and dendrites. Overexpression of DISC1 impairs associative memory. Experiments with deletion/mutation constructs have revealed the importance of amino-terminal domain (46-290) for memory suppression whereas carboxyl domain (598-854) and the amino-terminal residues (1-45) including the nuclear localization signal (NLS1) are dispensable. DISC1 overexpression also causes suppression of axonal and dendritic branching of mushroom body neurons, which mediate a variety of cognitive functions in the fly brain. Analyses with deletion/mutation constructs reveal that protein domains 598-854 and 349-402 are both required for the suppression of axonal branching, while amino-terminal domains including NLS1 are dispensable. In contrast, NLS1 was required for the suppression of dendritic branching, suggesting a mechanism involving gene expression. Moreover, domain 403-596 is also required for the suppression of dendritic branching. We also show that overexpression of DISC1 suppresses glutamatergic synaptogenesis in developing neuromuscular junctions. Deletion/mutation experiments have revealed the importance of protein domains 403-596 and 349-402 for synaptic suppression, while amino-terminal domains including NLS1 are dispensable. Finally, we show that DISC1 functionally interacts with the fly homolog of Dysbindin (DTNBP1) via direct protein-protein interaction in developing synapses.

DISC1 is a coordinator of intracellular trafficking to shape neuronal development and connectivity

The long, asymmetric and specialised architecture of neuronal processes necessitates a properly regulated transport network of molecular motors and cytoskeletal tracks. This allows appropriate distribution of cargo for correct formation and activity of the synapse, and thus normal neuronal communication. This communication is impaired in psychiatric disease, and ongoing studies have proposed that Disrupted in schizophrenia 1 (DISC1) is an important genetic risk factor for these disorders. The mechanisms by which DISC1 dysfunction might increase propensity to psychiatric disease are not completely understood; however, an emerging theme is that DISC1 can function as a key regulator of neuronal intracellular trafficking. Transport of a wide range of potential cargoes - including mRNAs, neurotransmitter receptors, vesicles and mitochondria - can be modulated by DISC1, and therefore is susceptible to DISC1 dysfunction. This theme highlights the importance of understanding precisely how DISC1 can regulate intracellular trafficking, and suggests that a novel approach to the treatment of psychiatric disorders could be provided by targeting this protein and the trafficking machinery with which it interacts.

DISC1-dependent Regulation of Mitochondrial Dynamics Controls the Morphogenesis of Complex Neuronal Dendrites

The DISC1 protein is implicated in major mental illnesses including schizophrenia, depression, bipolar disorder, and autism. Aberrant mitochondrial dynamics are also associated with major mental illness. DISC1 plays a role in mitochondrial transport in neuronal axons, but its effects in dendrites have yet to be studied. Further, the mechanisms of this regulation and its role in neuronal development and brain function are poorly understood. Here we have demonstrated that DISC1 couples to the mitochondrial transport and fusion machinery via interaction with the outer mitochondrial membrane GTPase proteins Miro1 and Miro2, the TRAK1 and TRAK2 mitochondrial trafficking adaptors, and the mitochondrial fusion proteins (mitofusins). Using live cell imaging, we show that disruption of the DISC1-Miro-TRAK complex inhibits mitochondrial transport in neurons. We also show that the fusion protein generated from the originally described DISC1 translocation (DISC1-Boymaw) localizes to the mitochondria, where it similarly disrupts mitochondrial dynamics. We also show by super resolution microscopy that DISC1 is localized to endoplasmic reticulum contact sites and that the DISC1-Boymaw fusion protein decreases the endoplasmic reticulum-mitochondria contact area. Moreover, disruption of mitochondrial dynamics by targeting the DISC1-Miro-TRAK complex or upon expression of the DISC1-Boymaw fusion protein impairs the correct development of neuronal dendrites. Thus, DISC1 acts as an important regulator of mitochondrial dynamics in both axons and dendrites to mediate the transport, fusion, and cross-talk of these organelles, and pathological DISC1 isoforms disrupt this critical function leading to abnormal neuronal development.

The CCDC55 couples cannabinoid receptor CNR1 to a putative DISC1 schizophrenia pathway

PURPOSE

Our previous study suggested that the coiled coil domain-containing 55 gene (CCDC55), also named as NSRP1 (nuclear speckle splicing regulatory protein 1 (NSRP1)), was encompassed in a haplotype block spanning over the serotonin transporter (5-HTT) gene in patients with schizophrenia (SCZ). However, the neurobiological function of CCDC55 gene remains unknown. This study aims to uncover the potential role of CCDC55 in SCZ-associated molecular pathways.

EXPERIMENTAL DESIGN

Using molecular cloning, sequencing and immune blotting to identify basic properties, yeast two-hybrid screening and glutathione S-transferase (GST) pull-down assay to test protein-protein interaction, and confocal laser scanning microscopy (CSLM) to show intracellular interaction of proteins.

PRINCIPAL FINDINGS

(i) CCDC55 is expressed as a nuclear protein in human neuronal cells; (ii) Protein-protein interaction analyses showed CCDC55 physically interacted with Ran binding protein 9 (RanBP9) and disrupted in schizophrenia 1 (DISC1); (iii) CCDC55 and RanBP9 co-localized in the nucleus of human neuronal cells; (iv) CCDC55 also interacted with the cannabinoid receptor 1 (CNR1), and with the brain cannabinoid receptor-interacting protein 1a (CNRIP1a); (v) CNR1 activation in differentiated human neuronal cells resulted in an altered RanBP9 localization.

CONCLUSION

CCDC55 may be involved in a functional bridging between the CNR1 activation and the DISC1/RanBP9-associated pathways.

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 Disc1 mutation differentially affects neurites and spines in hippocampal and cortical neurons

A balanced chromosomal translocation segregating with schizophrenia and affective disorders in a large Scottish family disrupting DISC1 implicated this gene as a susceptibility gene for major mental illness. Here we study neurons derived from a genetically engineered mouse strain with a truncating lesion disrupting the endogenous Disc1 ortholog. We provide a detailed account of the consequences of this mutation on axonal and dendritic morphogenesis as well as dendritic spine development in cultured hippocampal and cortical neurons. We show that the mutation has distinct effects on these two types of neurons, supporting a cell-type specific role of Disc1 in establishing structural connections among neurons. Moreover, using a validated antibody we provide evidence indicating that Disc1 localizes primarily to Golgi apparatus-related vesicles. Our results support the notion that in vitro cultures derived from Disc1(Tm1Kara) mice provide a valuable model for future mechanistic analysis of the cellular and biochemical effects of this mutation, and can thus serve as a platform for drug discovery efforts.

Molecular links between mitochondrial dysfunctions and schizophrenia

Schizophrenia is a complex neuropsychiatric disorder with both neurochemical and neurodevelopmental components in the pathogenesis. Growing pieces of evidence indicate that schizophrenia has pathological components that can be attributable to the abnormalities of mitochondrial function, which is supported by the recent finding suggesting mitochondrial roles for Disrupted-in-Schizophrenia 1 (DISC1). In this minireview, we briefly summarize the current understanding of the molecular links between mitochondrial dysfunctions and the pathogenesis of schizophrenia, covering recent findings from human genetics, functional genomics, proteomics, and molecular and cell biological approaches.

Molecular characterization of disrupted in schizophrenia-1 risk variant S704C reveals the formation of altered oligomeric assembly

DISC1 (Disrupted in schizophrenia-1) plays essential roles in neuronal proliferation, neuronal migration and axon guidance and has been implicated in schizophrenia and related psychiatric disorders. DISC1 forms a functional complex with nuclear distribution element-like protein-1 (NDEL1), a key component that regulates microtubule organization during cell division and neuronal migration. DISC1 polymorphisms at the binding interface of DISC1-NDEL1 complex have been implicated in schizophrenia. However, it is unknown how schizophrenia risk polymorphisms perturb its interaction with NDEL1 and how they change the inherent biochemical properties of DISC1. Here, we characterize the oligomerization and binding property of DISC1 and its natural schizophrenia risk variant, S704C. Our results show that DISC1 forms octamers via dimers as building blocks and directly interacts with tetramers of NDEL1. The schizophrenia risk variant S704C affects the formation of octamers of DISC1 and exhibits higher-order self-oligomerization. However, the observed formation of new oligomeric species did not influence its binding with NDEL1. These results suggest that the improper oligomeric assembly of DISC1-S704C may underlie the observed phenotypic variation due to the polymorphism.

Linking neurodevelopmental and synaptic theories of mental illness through DISC1

Recent advances in our understanding of the underlying genetic architecture of psychiatric disorders has blown away the diagnostic boundaries that are defined by currently used diagnostic manuals. The disrupted in schizophrenia 1 (DISC1) gene was originally discovered at the breakpoint of an inherited chromosomal translocation, which segregates with major mental illnesses. In addition, many biological studies have indicated a role for DISC1 in early neurodevelopment and synaptic regulation. Given that DISC1 is thought to drive a range of endophenotypes that underlie major mental conditions, elucidating the biology of DISC1 may enable the construction of new diagnostic categories for mental illnesses with a more meaningful biological foundation.

DISC1: Structure, Function, and Therapeutic Potential for Major Mental Illness

Disrupted in schizophrenia 1 (DISC1) is well established as a genetic risk factor across a spectrum of psychiatric disorders, a role supported by a growing body of biological studies, making the DISC1 protein interaction network an attractive therapeutic target. By contrast, there is a relative deficit of structural information to relate to the myriad biological functions of DISC1. Here, we critically appraise the available bioinformatics and biochemical analyses on DISC1 and key interacting proteins, and integrate this with the genetic and biological data. We review, analyze, and make predictions regarding the secondary structure and propensity for disordered regions within DISC1, its protein-interaction domains, subcellular localization motifs, and the structural and functional implications of common and ultrarare DISC1 variants associated with major mental illness. We discuss signaling pathways of high pharmacological potential wherein DISC1 participates, including those involving phosphodiesterase 4 (PDE4) and glycogen synthase kinase 3 (GSK3). These predictions and priority areas can inform future research in the translational and potentially guide the therapeutic processes.

Convergence of two independent mental disease genes on the protein level: recruitment of dysbindin to cell-invasive disrupted-in-schizophrenia 1 aggresomes

BACKGROUND

Both disrupted-in-schizophrenia 1 (DISC1) and dysbindin have been identified as schizophrenia candidate genes in independent genetic linkage studies. The proteins have been assigned distinct subcellular locations and functions. We investigated whether both proteins converge into a common pathway specific for schizophrenia or mental diseases.

METHODS

DISC1 and dysbindin were expressed as recombinant proteins with or without a fluorescent protein-tag in human or mouse neuroblastoma cells and as recombinant proteins in E. coli. Postmortem brains of patients with mental diseases from the Stanley Research Medical Institute's Consortium Collection were used to demonstrate molecular interactions in biochemically purified protein fractions.

RESULTS

First, upon overexpression in neuroblastoma cells, DISC1 formed aggresomes that recruited homologous soluble C-terminal DISC1 fragment or heterologous dysbindin. Domains involved in binding could be mapped to DISC1 (316-597) and dysbindin (82-173), indicating a specific interaction. In addition, recruitment was demonstrated when externally added, purified DISC1 aggresomes penetrated recipient cells after coincubation. Second, a direct interaction between soluble DISC1 protein and dysbindin was demonstrated in a cell free system using E. coli-expressed proteins. Third, co-aggregation of DISC1 and dysbindin was demonstrated in postmortem brains for a subgroup of cases with chronic mental disease but not healthy control subjects.

CONCLUSIONS

A direct interaction of soluble and insoluble DISC1 protein with dysbindin protein demonstrates convergence of so far considered independent mental disease genes by direct molecular interaction. Our findings highlight protein aggregation and recruitment as a biological mechanism in mental disease.

The psychiatric disease risk factors DISC1 and TNIK interact to regulate synapse composition and function

Disrupted in schizophrenia 1 (DISC1), a genetic risk factor for multiple serious psychiatric diseases including schizophrenia, bipolar disorder and autism, is a key regulator of multiple neuronal functions linked to both normal development and disease processes. As these diseases are thought to share a common deficit in synaptic function and architecture, we have analyzed the role of DISC1 using an approach that focuses on understanding the protein-protein interactions of DISC1 specifically at synapses. We identify the Traf2 and Nck-interacting kinase (TNIK), an emerging risk factor itself for disease, as a key synaptic partner for DISC1, and provide evidence that the DISC1-TNIK interaction regulates synaptic composition and activity by stabilizing the levels of key postsynaptic density proteins. Understanding the novel DISC1-TNIK interaction is likely to provide insights into the etiology and underlying synaptic deficits found in major psychiatric diseases.

Regulation of the cytoskeleton by Disrupted-in-schizophrenia 1 (DISC1)

Disrupted in schizophrenia 1 (DISC1) is one of the strongest supported risk genes for psychiatric disorders, such as schizophrenia, major depression, bipolar disorder, and autism. Intensive study over the past 11 years, since the gene was cloned, has tried to understand at the molecular and cellular levels how mutations in DISC1 contribute to these diseases. The DISC1 protein has been reported to be localized to cytoskeleton-rich regions in cells, including the centrosome, base of primary cilia, axon and dendritic shafts and spines. Here we review the functions of DISC1 which are relevant for cytoskeletal regulation and its crucial roles during normal brain development and in adult brain function. This article is part of a Special Issue entitled Neuronal Function.

Disrupted-in-schizophrenia 1 (DISC1) plays essential roles in mitochondria in collaboration with Mitofilin

Disrupted-in-schizophrenia 1 (DISC1) has emerged as a schizophrenia-susceptibility gene affecting various neuronal functions. In this study, we characterized Mitofilin, a mitochondrial inner membrane protein, as a mediator of the mitochondrial function of DISC1. A fraction of DISC1 was localized to the inside of mitochondria and directly interacts with Mitofilin. A reduction in DISC1 function induced mitochondrial dysfunction, evidenced by decreased mitochondrial NADH dehydrogenase activities, reduced cellular ATP contents, and perturbed mitochondrial Ca(2+) dynamics. In addition, deficiencies in DISC1 and Mitofilin induced a reduction in mitochondrial monoamine oxidase-A activity. The mitochondrial dysfunctions evoked by the deficiency of DISC1 were partially phenocopied by an overexpression of truncated DISC1 that is associated with schizophrenia in human. DISC1 deficiencies induced the ubiquitination of Mitofilin, suggesting that DISC1 is critical for the stability of Mitofilin. Finally, the mitochondrial dysfunction induced by DISC1 deficiency was partially reversed by coexpression of Mitofilin, confirming a functional link between DISC1 and Mitofilin for the normal mitochondrial function. According to these results, we propose that DISC1 plays essential roles for mitochondrial function in collaboration with a mitochondrial interacting partner, Mitofilin.

Mitochondrial dysfunction and pathology in bipolar disorder and schizophrenia

Bipolar disorder (BPD) and schizophrenia (SZ) are severe psychiatric illnesses with a combined prevalence of 4%. A disturbance of energy metabolism is frequently observed in these disorders. Several pieces of evidence point to an underlying dysfunction of mitochondria: (i) decreased mitochondrial respiration; (ii) changes in mitochondrial morphology; (iii) increases in mitochondrial DNA (mtDNA) polymorphisms and in levels of mtDNA mutations; (iv) downregulation of nuclear mRNA molecules and proteins involved in mitochondrial respiration; (v) decreased high-energy phosphates and decreased pH in the brain; and (vi) psychotic and affective symptoms, and cognitive decline in mitochondrial disorders. Furthermore, transgenic mice with mutated mitochondrial DNA polymerase show mood disorder-like phenotypes. In this review, we will discuss the genetic and physiological components of mitochondria and the evidence for mitochondrial abnormalities in BPD and SZ. We will furthermore describe the role of mitochondria during brain development and the effect of current drugs for mental illness on mitochondrial function. Understanding the role of mitochondria, both developmentally as well as in the ailing brain, is of critical importance to elucidate pathophysiological mechanisms in psychiatric disorders.

Additive effect of NRG1 and DISC1 genes on lateral ventricle enlargement in first episode schizophrenia

Neuregulin 1 (NRG1) and Disrupted-in-schizophrenia (DISC1) genes, which are candidate genes for schizophrenia, are implicated in brain development. We have previously reported an association between the T allele of the rs6994992 SNP within NRG1 gene and lateral ventricle (LV) enlargement in first-episode schizophrenia patients. Moreover, transgenic mice with mutant DISC1 have also been reported as showing LV enlargement. In this study, we examined the possible interactive effects of NRG1 and DISC1 on brain volumes in a sample of first-episode schizophrenia patients. Ninety-one patients experiencing their first episode of schizophrenia underwent genotyping of three SNPs within DISC1 and structural brain MRI. These results were combined with our previously reported genotypes on three SNPs within NRG1. The T/T genotype of rs2793092 SNP in DISC1 was significantly associated with increased LV volume. However, taking into account the rs6994992 SNP in the NRG1 gene, which was also associated with LV volume in a previous study, the DISC1 SNP only predicted LV enlargement among those patients carrying the T allele in the NRG1 SNP. Those patients with the "at risk" allelic combinations in both genes had LV volumes which were 48% greater than those with none of the allelic combinations. Our findings suggest that NRG1 and DISC1 genes may be associated with brain abnormalities in schizophrenia through their influence on related pathways of brain development.

Disc1 regulates foxd3 and sox10 expression, affecting neural crest migration and differentiation

This work reports the characterization and functional analysis of disrupted in schizophrenia 1 (disc1), a well-documented schizophrenia-susceptibility gene, in zebrafish cranial neural crest (CNC). Our data demonstrated that disc1 was expressed in zebrafish CNC cells. Loss of Disc1 resulted in persistent CNC cell medial migration, dorsal to the developing neural epithelium, and hindered migration away from the region dorsal to the neural rod. General CNC cell motility was not affected by Disc1 knockdown, however, as the speed of CNC cells was indistinguishable from that of wild-type counterparts. We determined that the failure of CNC cells to migrate away from the neural rod correlated with the enhanced expression of two transcription factors, foxd3 and sox10. These transcription factors have many functions in CNC cells, including the maintenance of precursor pools, timing of migration onset, and the induction of cell differentiation. Our work, in conjunction with previous studies, suggests that the perpetuation of expression of these factors affects several aspects of CNC cell development, leading to a loss of craniofacial cartilage and an expansion of peripheral cranial glia. Based on our data, we propose a model in which Disc1 functions in the transcriptional repression of foxd3 and sox10, thus mediating CNC cell migration and differentiation.

Association of the SerCys DISC1 polymorphism with human hippocampal formation gray matter and function during memory encoding

A common nonsynonymous single nucleotide polymorphism leading to a serine-to-cysteine substitution at amino acid 704 (Ser(704)Cys) in the DISC1 protein sequence has been recently associated with schizophrenia and with specific hippocampal abnormalities. Here, we used multimodal neuroimaging to investigate in a large sample of healthy subjects the putative association of the Ser(704)Cys DISC1 polymorphism with in vivo brain phenotypes including hippocampal formation (HF) gray matter volume and function (as assessed with functional MRI) as well as HF functional coupling with the neural network engaged during encoding of recognition memory. Individuals homozygous for DISC1 Ser allele relative to carriers of the Cys allele showed greater gray matter volume in the HF. Further, Ser/Ser subjects exhibited greater engagement of the HF together with greater HF-dorsolateral prefrontal cortex functional coupling during memory encoding, in spite of similar behavioral performance. These findings consistently support the notion that Ser(704)Cys DISC1 polymorphism is physiologically relevant. Moreover, they support the hypothesis that genetic variation in DISC1 may affect the risk for schizophrenia by modifying hippocampal gray matter and function.

Nuclear DISC1 regulates CRE-mediated gene transcription and sleep homeostasis in the fruit fly

Disrupted-in-schizophrenia-1 (DISC1) is one of major susceptibility factors for a wide range of mental illnesses, including schizophrenia, bipolar disorder, major depression and autism spectrum conditions. DISC1 is located in several subcellular domains, such as the centrosome and the nucleus, and interacts with various proteins, including NudE-like (NUDEL/NDEL1) and activating transcription factor 4 (ATF4)/CREB2. Nevertheless, a role for DISC1 in vivo remains to be elucidated. Therefore, we have generated a Drosophila model for examining normal functions of DISC1 in living organisms. DISC1 transgenic flies with preferential accumulation of exogenous human DISC1 in the nucleus display disturbance in sleep homeostasis, which has been reportedly associated with CREB signaling/CRE-mediated gene transcription. Thus, in mammalian cells, we characterized nuclear DISC1, and identified a subset of nuclear DISC1 that colocalizes with the promyelocytic leukemia (PML) bodies, a nuclear compartment for gene transcription. Furthermore, we identified three functional cis-elements that regulate the nuclear localization of DISC1. We also report that DISC1 interacts with ATF4/CREB2 and a corepressor N-CoR, modulating CRE-mediated gene transcription.

Mitochondrial disorders in the nervous system

Mitochondrial diseases (encephalomyopathies) have traditionally been ascribed to defects of the respiratory chain, which has helped researchers explain their genetic and clinical complexity. However, other mitochondrial functions are greatly important for the nervous system, including protein importation, organellar dynamics, and programmed cell death. Defects in genes controlling these functions are attracting increasing attention as causes not only of neurological (and psychiatric) diseases but also of age-related neurodegenerative disorders. After discussing some pathogenic conundrums regarding the neurological manifestations of the respiratory chain defects, we review altered mitochondrial dynamics in the etiology of specific neurological diseases and in the physiopathology of more common neurodegenerative disorders.

Dual constraints on synapse formation and regression in schizophrenia: neuregulin, neuroligin, dysbindin, DISC1, MuSK and agrin

During adolescence there is a loss of approximately 30% of the synapses formed in the cortex during childhood. Comprehensive studies of the visual cortex show that this loss of synapses does not occur as a consequence of less appropriate projections being eliminated in favour of more appropriate ones. Rather it seems that synapses with low efficacy for transmission are eliminated in favour of those with higher efficacy. The loss of low-efficacy synapses is known, on theoretical grounds, to enhance the function of neural networks, but large synapse losses lead to failure of network function. In the dorsolateral prefrontal cortex (DLPC) of those suffering from schizophrenia the number of synapses is relatively very low, approximately 60% lower than that observed in normal childhood. It is not known if this is due to an additional loss over that during normal adolescence or whether it results from a failure to form a normal complement of synapses during childhood. The first study of synapse loss in the mammalian nervous system was made on the neuromuscular junction at Sydney University in 1974. Since then this junction has provided principal insights into the molecular basis of synapse formation and regression, so providing a paradigm for investigations of these phenomena in the DLPC. For example the molecules muscle-specific receptor tyrosine kinase (MuSK), agrin and neuregulin have been identified and their critical roles in the formation and maintenance of synapses elucidated. Loss of function of MuSK or agrin leads to failure of neuromuscular synapse formation as well as a loss of approximately 30% of excitatory synapses in the cortex. Similar synapse loss occurs on failure of neuregulin in vitro and of neuroligin in vivo. It is suggested that three important questions need to be answered: first, over what development period are the synapse numbers in DLPC of subjects with schizophrenia lower than normal; second, what are the relative importance of MuSK/agrin, neuregulin/ErB and neurexin/neuroligin in synapse formation and regression in the DLPC; and third, to what extent have these molecules gone awry in schizophrenia.

Inducible expression of mutant human DISC1 in mice is associated with brain and behavioral abnormalities reminiscent of schizophrenia

A strong candidate gene for schizophrenia and major mental disorders, disrupted-in-schizophrenia 1 (DISC1) was first described in a large Scottish family in which a balanced chromosomal translocation segregates with schizophrenia and other psychiatric illnesses. The translocation mutation may result in loss of DISC1 function via haploinsufficiency or dominant-negative effects of a predicted mutant DISC1 truncated protein product. DISC1 has been implicated in neurodevelopment, including maturation of the cerebral cortex. To evaluate the neuronal and behavioral effects of mutant DISC1, the Tet-off system under the regulation of the CAMKII promoter was used to generate transgenic mice with inducible expression of mutant human DISC1 (hDISC1) limited to forebrain regions, including cerebral cortex, hippocampus and striatum. Expression of mutant hDISC1 was not associated with gross neurodevelopmental abnormalities, but led to a mild enlargement of the lateral ventricles and attenuation of neurite outgrowth in primary cortical neurons. These morphological changes were associated with decreased protein levels of endogenous mouse DISC1, LIS1 and SNAP-25. Compared to their sex-matched littermate controls, mutant hDISC1 transgenic male mice exhibited spontaneous hyperactivity in the open field and alterations in social interaction, and transgenic female mice showed deficient spatial memory. The results show that the neuronal and behavioral effects of mutant hDISC1 are consistent with a dominant-negative mechanism, and are similar to some features of schizophrenia. The present mouse model may facilitate the study of aspects of the pathogenesis of schizophrenia.

The DISC locus in psychiatric illness

The DISC locus is located at the breakpoint of a balanced t(1;11) chromosomal translocation in a large and unique Scottish family. This translocation segregates in a highly statistically significant manner with a broad diagnosis of psychiatric illness, including schizophrenia, bipolar disorder and major depression, as well as with a narrow diagnosis of schizophrenia alone. Two novel genes were identified at this locus and due to the high prevalence of schizophrenia in this family, they were named Disrupted-in-Schizophrenia-1 (DISC1) and Disrupted-in-Schizophrenia-2 (DISC2). DISC1 encodes a novel multifunctional scaffold protein, whereas DISC2 is a putative noncoding RNA gene antisense to DISC1. A number of independent genetic linkage and association studies in diverse populations support the original linkage findings in the Scottish family and genetic evidence now implicates the DISC locus in susceptibility to schizophrenia, schizoaffective disorder, bipolar disorder and major depression as well as various cognitive traits. Despite this, with the exception of the t(1;11) translocation, robust evidence for a functional variant(s) is still lacking and genetic heterogeneity is likely. Of the two genes identified at this locus, DISC1 has been prioritized as the most probable candidate susceptibility gene for psychiatric illness, as its protein sequence is directly disrupted by the translocation. Much research has been undertaken in recent years to elucidate the biological functions of the DISC1 protein and to further our understanding of how it contributes to the pathogenesis of schizophrenia. These data are the main subject of this review; however, the potential involvement of DISC2 in the pathogenesis of psychiatric illness is also discussed. A detailed picture of DISC1 function is now emerging, which encompasses roles in neurodevelopment, cytoskeletal function and cAMP signalling, and several DISC1 interactors have also been defined as independent genetic susceptibility factors for psychiatric illness. DISC1 is a hub protein in a multidimensional risk pathway for major mental illness, and studies of this pathway are opening up opportunities for a better understanding of causality and possible mechanisms of intervention.

Association of distinct allelic haplotypes of DISC1 with psychotic and bipolar spectrum disorders and with underlying cognitive impairments

Bipolar disorder (BPD) and schizophrenia (SCZ) have at least a partially convergent aetiology and thus may share genetic susceptibility loci. Multiple lines of evidence emphasize the role of disrupted-in-schizophrenia-1 (DISC1) gene in psychotic disorders such as SCZ. We monitored the association of allelic variants of translin-associated factor X (TSNAX)/DISC1 gene cluster using 13 single-nucleotide polymorphisms (SNPs) in 723 members of 179 Finnish BPD families. Consistent with an earlier finding in Finnish SCZ families, the haplotype T-A of rs751229 and rs3738401 at the 5' end of DISC1 was over-transmitted to males with psychotic disorder (P = 0.008; for an extended haplotype P = 0.0007 with both genders). Haplotypes at the 3' end of DISC1 associated with bipolar spectrum disorder (P = 0.0002 for an under-transmitted haplotype T-T of rs821616 and rs1411771, for an extended haplotype P = 0.0001), as did a two-SNP risk haplotype at the 5' end of TSNAX (P = 0.007). The risk haplotype for psychotic disorder also associated to perseverations (P = 0.035; for rs751229 alone P = 0.0012), and a protective haplotype G-T-G with rs1655285 in addition to auditory attention (P = 0.0059). The 3' end variants associated with several cognitive traits, with the most robust signal for rs821616 and verbal fluency and rs980989 and psychomotor processing speed (P = 0.011 for both). These results support involvement of DISC1 in the genetic aetiology of BPD and suggest that its distinct variants contribute to variation in the dimensional features of psychotic and bipolar spectrum disorders. Finding of alternative associating haplotypes in the same set of BPD families gives evidence for allelic heterogeneity within DISC1, eventually leading to heterogeneity in the clinical outcome as well.

PC12 cell model of inducible expression of mutant DISC1: new evidence for a dominant-negative mechanism of abnormal neuronal differentiation

A balanced chromosomal translocation, segregating with mental illnesses in a large Scottish family, interrupts the disrupted-in-schizophrenia 1 (DISC1) gene, which would result in loss of DISC1 function via haploinsufficiency or dominant-negative effects (or possibly could cause gain-of-function effects) if a truncated protein is present. To evaluate the effects of a predicted protein, mutant DISC1, we generated stable PC12 cell clones with inducible expression of mutant or full-length human DISC1 (hDISC1). Our study presents new observations that the inhibitory effects of mutant hDISC1 on NGF-induced neurite outgrowth are dependent on the level and timing of expression of mutant DISC1 and the concentrations of NGF, and are associated with altered sub-cellular distribution of endogenous DISC1 and ATF4, and decreased protein levels of LIS1. Thus, inducible expression of DISC1 in PC12 cell clones is a valuable in vitro model for further studying the molecular mechanisms likely due to loss of function of DISC1 relevant to the pathogenesis of major mental illnesses.

Disrupted in Schizophrenia 1 Interactome: evidence for the close connectivity of risk genes and a potential synaptic basis for schizophrenia

Disrupted in Schizophrenia 1 (DISC1) is a schizophrenia risk gene associated with cognitive deficits in both schizophrenics and the normal ageing population. In this study, we have generated a network of protein-protein interactions (PPIs) around DISC1. This has been achieved by utilising iterative yeast-two hybrid (Y2H) screens, combined with detailed pathway and functional analysis. This so-called 'DISC1 interactome' contains many novel PPIs and provides a molecular framework to explore the function of DISC1. The network implicates DISC1 in processes of cytoskeletal stability and organisation, intracellular transport and cell-cycle/division. In particular, DISC1 looks to have a PPI profile consistent with that of an essential synaptic protein, which fits well with the underlying molecular pathology observed at the synaptic level and the cognitive deficits seen behaviourally in schizophrenics. Utilising a similar approach with dysbindin (DTNBP1), a second schizophrenia risk gene, we show that dysbindin and DISC1 share common PPIs suggesting they may affect common biological processes and that the function of schizophrenia risk genes may converge.

Schizophrenia in translation: disrupted in schizophrenia (DISC1): integrating clinical and basic findings

The disrupted in schizophrenia 1 (DISC1) gene has been linked to schizophrenia and other serious mental illnesses in multiple pedigrees. This article will review the neurobiology of DISC1 in normal developing and adult brain and the putative role of the mutant form in major mental illness, particularly schizophrenia. The initial genetic finding of an association between DISC1 and schizophrenia in a Scottish population has now been replicated in Finnish, American, Japanese, and Taiwanese populations. DISC1 is present throughout the brain of a variety of species during development and adulthood, including many of the brain regions known to be abnormal in schizophrenia, such as the prefrontal cortex, hippocampus, and thalamus. The functions of DISC1 in the developing brain include neuronal migration, neurite outgrowth, and neurite extension. In the adult, DISC1 has been identified in multiple populations of neurons and in structures associated with synaptic function, suggesting that one of its adult functions may be synaptic plasticity. DISC1 is associated with numerous cognitive functions that are abnormal in schizophrenia. Converging evidence from cell culture, mice mutants, postmortem brain, and genetics implicates mutant DISC1 in the pathophysiology of schizophrenia and other mental illnesses.

Functional genomics in postmortem human brain: abnormalities in a DISC1 molecular pathway in schizophrenia

The disrupted in schizophrenia 1 (DISC1) gene has been identified as a schizophrenia susceptibility gene based on linkage and single nucleotide polymorphism (SNP) association studies and clinical data, suggesting that risk SNPs impact on hippocampal structure and function. We hypothesized that altered expression of DISC1 andlor its molecular partners (nuclear distribution element-like [NUDEL], fasciculation and elongation protein zeta-1 [FEZ1], and lissencephaly 1 [L1S1 ]) may underlie its pathogenic role in schizophrenia and explain its genetic association. We examined the expression of DISC1 and its binding partners in the hippocampus and dorsolateral prefrontal cortex of postmortem human brains of schizophrenic patients and controls. We found no difference in the expression of DISC1 mRNA in schizophrenia, and no association with previously identified risk SNPs, However, the expression of NUDEL, FEZ1, and LIS1 vas significantly reduced in tissue from schizophrenic subjects, and the expression of each showed association with high-risk DISC1 polymorphisms. These data suggest involvement of genetically linked abnormalities in the DISC1 molecular pathway in the pathophysiology of schizophrenia.

The genetics and biology of DISC1--an emerging role in psychosis and cognition

In the developing field of biological psychiatry, DISC1 stands out by virtue of there being credible evidence, both genetic and biological, for a role in determining susceptibility to schizophrenia and related disorders. We highlight the methodologic paradigm that led to identification of DISC1 and review the supporting genetic and biological evidence. The original finding of DISC1 as a gene disrupted by a balanced translocation on chromosome 1q42 that segregates with schizophrenia, bipolar disorder, and recurrent major depression has sparked a number of confirmatory linkage and association studies. These indicate that DISC1 is a generalizable genetic risk factor for psychiatric illness that also influences cognition in healthy subjects. DISC1 has also been shown to interact with a number of proteins with neurobiological pedigrees, including Ndel1 (NUDEL), a key regulator of neuronal migration with endo-oligopeptidase activity, and PDE4B, a phosphodiesterase that is critical for cyclic adenosine monophosphate signaling and that is directly linked to learning, memory, and mood. Both are potential "drug" targets. DISC1 has thus emerged as a key molecular player in the etiology of major mental illness and in normal brain processes.

Genes and schizophrenia: beyond schizophrenia: the role of DISC1 in major mental illness

Schizophrenia and related disorders have a major genetic component, but despite much effort and many claims, few genes have been consistently replicated and fewer have biological support. One recent exception is "Disrupted in Schizophrenia 1" (DISC1), which was identified at the breakpoint on chromosome 1 of the balanced translocation (1;11)(q42.1;q14.3) that co-segregated in a large Scottish family with a wide spectrum of major mental illnesses. Since then, genetic analysis has implicated DISC1 in schizophrenia, schizoaffective disorder, bipolar affective disorder, and major depression. Importantly, evidence is emerging from genetic studies for a causal relationship between DISC1 and directly measurable trait variables such as working memory, cognitive aging, and decreased gray matter volume in the prefrontal cortex, abnormalities in hippocampal structure and function, and reduction in the amplitude of the P300 event-related potential. Further, DISC1 binds a number of proteins known to be involved in essential processes of neuronal function, including neuronal migration, neurite outgrowth, cytoskeletal modulation, and signal transduction. Thus, both genetic and functional data provide evidence for a critical role for DISC1 in schizophrenia and related disorders, supporting the neurodevelopmental hypothesis for the molecular pathogenesis of these devastating illnesses.

A review of Disrupted-In-Schizophrenia-1 (DISC1): neurodevelopment, cognition, and mental conditions

Disrupted-In-Schizophrenia-1 (DISC1) is a promising candidate gene for schizophrenia (SZ) and bipolar disorder (BP), but its basic biology remains to be elucidated. Accumulating genetic evidence supports that DISC1 is associated with some aspects of cognitive functions relevant to SZ and BP. Here, we provide a summary of the current updates in biological studies of DISC1. Disrupted-In-Schizophrenia-1, preferentially expressed in the forebrain, has multiple isoforms with potential posttranslational modifications. Disrupted-In-Schizophrenia-1 protein occurs in multiple subcellular compartments, which include the centrosome, microtubule fractions, postsynaptic densities, actin cytoskeletal fractions, the mitochondria, and the nucleus. Recent studies have clarified that DISC1 mediates at least centrosome-dynein cascade and cyclic adenosine monophosphate (cAMP) signaling. Furthermore, both cytogenetic and cell biological studies consistently suggest that an overall loss of DISC1 function (either haploinsufficiency or dominant-negative, or both) may be associated with SZ and BP. On the basis of these findings, production of DISC1 genetically engineered mice is proposed as a promising animal model for SZ and BP. Several groups are currently generating DISC1 mice and starting to characterize them. In this review, the advantages and disadvantages of each animal model are discussed.

Genetic mouse models of schizophrenia: from hypothesis-based to susceptibility gene-based models

Translation of human genetic mutations into genetic mouse models is an important strategy to study the pathogenesis of schizophrenia, identify potential drug targets, and test new drugs for new antipsychotic treatments. Although it is impossible to recapitulate the full spectrum of schizophrenia symptoms in animal models, hypothesis-driven genetic mouse models have been successful in reproducing several schizophrenia-like behaviors and uncovering the roles of specific genes in dopamine and glutamine neurotransmission systems in mediating schizophrenia-like behaviors. Recent discoveries of susceptibility genes for schizophrenia and recognition of cognitive dysfunction as a core feature of schizophrenia and a phenotype of susceptibility for schizophrenia offer opportunities to develop newer genetic mouse models based on susceptibility. This new generation of genetic mouse models could shed light on the etiology of schizophrenia and lead us to new hypotheses, novel diagnostic tools, and more effective therapy.

Expression of DISC1 binding partners is reduced in schizophrenia and associated with DISC1 SNPs

DISC1 has been identified as a schizophrenia susceptibility gene based on linkage and SNP association studies and clinical data suggesting that risk SNPs impact on hippocampal structure and function. In cell and animal models, C-terminus-truncated DISC1 disrupts intracellular transport, neural architecture and migration, perhaps because it fails to interact with binding partners involved in neuronal differentiation such as fasciculation and elongation protein zeta-1 (FEZ1), platelet-activating factor acetylhydrolase, isoform Ib, PAFAH1B1 or lissencephaly 1 protein (LIS1) and nuclear distribution element-like (NUDEL). We hypothesized that altered expression of DISC1 and/or its molecular partners may underlie its pathogenic role in schizophrenia and explain its genetic association. We examined the expression of DISC1 and these selected binding partners as well as reelin, a protein in a related signaling pathway, in the hippocampus and dorsolateral prefrontal cortex of postmortem human brain patients with schizophrenia and controls. We found no difference in the expression of DISC1 or reelin mRNA in schizophrenia and no association with previously identified risk DISC1 SNPs. However, the expression of NUDEL, FEZ1 and LIS1 was each significantly reduced in the brain tissue from patients with schizophrenia and expression of each showed association with high-risk DISC1 polymorphisms. Although, many other DISC1 binding partners still need to be investigated, these data implicate genetically linked abnormalities in the DISC1 molecular pathway in the pathophysiology of schizophrenia.

DISC1 immunoreactivity at the light and ultrastructural level in the human neocortex

Disrupted-In-Schizophrenia 1 (DISC1) is one of two genes that straddle the chromosome 1 breakpoint of a translocation associated with an increased risk of schizophrenia. DISC1 has been identified in the brain of various mammalian species, but no previous immunocytochemical studies have been conducted in human neocortex. We examined DISC1 immunoreactivity in frontal and parietal cortex (BA 4, 9, 39, and 46) in normal human brain. At the light microscopic level, immunolabeling was prominent in the neuropil, in multiple populations of cells, and in the white matter. At the ultrastructural level, staining was prominent in structures associated with synaptic function. Immunolabeled axon terminals comprised 8% of all terminals and formed both asymmetric and symmetric synapses. Labeled axon terminals formed synapses with labeled spines and dendrites; in some, only the postsynaptic density (PSD) of the postsynaptic structure was labeled. The most common configuration, however, was an unlabeled axon terminal forming an asymmetric synapse with a spine that had immunoreactivity deposited on the PSD and throughout the spine. The presence of DISC1 in multiple types of synapses suggests the involvement of DISC1 in corticocortical as well as thalamocortical connections. Staining was also present in ribosomes, parts of the chromatin, in dendritic shafts, and on some microtubules. Labeling was absent from the Golgi apparatus and multivesicular bodies, which are associated with protein excretion. These anatomical localization data suggest that DISC1 participates in synaptic activity and microtubule function, and are consistent with the limited data on its adult function.

A functional link between Disrupted-In-Schizophrenia 1 and the eukaryotic translation initiation factor 3

Disrupted-In-Schizophrenia 1 (DISC1) was identified as a candidate gene for schizophrenia. DISC1 is disrupted by a balanced t(1;11)(q42.1;q14.3) translocation segregating with schizophrenia and related psychiatric illness in a large Scottish family. Here, we show that DISC1 interacts via its globular domain with the p40 subunit of the eukaryotic translation initiation factor 3. Furthermore, we found that overexpression of DISC1 in SH-SY5Y cells induces the assembly of eIF3- and TIA-1-positive stress granules (SGs), discrete cytoplasmic granules formed in response to environmental stresses. Our findings suggest that DISC1 may function as a translational regulator and may be involved in stress response.