Familial t(1;11) translocation is associated with disruption of white matter structural integrity and oligodendrocyte-myelin dysfunction

Although the underlying neurobiology of major mental illness (MMI) remains unknown, emerging evidence implicates a role for oligodendrocyte-myelin abnormalities. Here, we took advantage of a large family carrying a balanced t(1;11) translocation, which substantially increases risk of MMI, to undertake both diffusion tensor imaging and cellular studies to evaluate the consequences of the t(1;11) translocation on white matter structural integrity and oligodendrocyte-myelin biology. This translocation disrupts among others the DISC1 gene which plays a crucial role in brain development. We show that translocation-carrying patients display significant disruption of  white matter integrity compared with familial controls. At a cellular level, we observe dysregulation of key pathways controlling oligodendrocyte development and morphogenesis in induced pluripotent stem cell (iPSC) derived case oligodendrocytes. This is associated with reduced proliferation and a stunted morphology in vitro. Further, myelin internodes in a humanized mouse model that recapitulates the human translocation as well as after transplantation of t(1;11) oligodendrocyte progenitors were significantly reduced when  compared with controls. Thus we provide evidence that the t(1;11) translocation has biological effects at both the systems and cellular level that together suggest oligodendrocyte-myelin dysfunction.

DISC1 regulates N-methyl-D-aspartate receptor dynamics: abnormalities induced by a Disc1 mutation modelling a translocation linked to major mental illness

The neuromodulatory gene DISC1 is disrupted by a t(1;11) translocation that is highly penetrant for schizophrenia and affective disorders, but how this translocation affects DISC1 function is incompletely understood. N-methyl-D-aspartate receptors (NMDAR) play a central role in synaptic plasticity and cognition, and are implicated in the pathophysiology of schizophrenia through genetic and functional studies. We show that the NMDAR subunit GluN2B complexes with DISC1-associated trafficking factor TRAK1, while DISC1 interacts with the GluN1 subunit and regulates dendritic NMDAR motility in cultured mouse neurons. Moreover, in the first mutant mouse that models DISC1 disruption by the translocation, the pool of NMDAR transport vesicles and surface/synaptic NMDAR expression are increased. Since NMDAR cell surface/synaptic expression is tightly regulated to ensure correct function, these changes in the mutant mouse are likely to affect NMDAR signalling and synaptic plasticity. Consistent with these observations, RNASeq analysis of the translocation carrier-derived human neurons indicates abnormalities of excitatory synapses and vesicle dynamics. RNASeq analysis of the human neurons also identifies many differentially expressed genes previously highlighted as putative schizophrenia and/or depression risk factors through large-scale genome-wide association and copy number variant studies, indicating that the translocation triggers common disease pathways that are shared with unrelated psychiatric patients. Altogether, our findings suggest that translocation-induced disease mechanisms are likely to be relevant to mental illness in general, and that such disease mechanisms include altered NMDAR dynamics and excitatory synapse function. This could contribute to the cognitive disorders displayed by translocation carriers.

Rare disruptive variants in the DISC1 Interactome and Regulome: association with cognitive ability and schizophrenia

Schizophrenia (SCZ), bipolar disorder (BD) and recurrent major depressive disorder (rMDD) are common psychiatric illnesses. All have been associated with lower cognitive ability, and show evidence of genetic overlap and substantial evidence of pleiotropy with cognitive function and neuroticism. Disrupted in schizophrenia 1 (DISC1) protein directly interacts with a large set of proteins (DISC1 Interactome) that are involved in brain development and signaling. Modulation of DISC1 expression alters the expression of a circumscribed set of genes (DISC1 Regulome) that are also implicated in brain biology and disorder. Here we report targeted sequencing of 59 DISC1 Interactome genes and 154 Regulome genes in 654 psychiatric patients and 889 cognitively-phenotyped control subjects, on whom we previously reported evidence for trait association from complete sequencing of the DISC1 locus. Burden analyses of rare and singleton variants predicted to be damaging were performed for psychiatric disorders, cognitive variables and personality traits. The DISC1 Interactome and Regulome showed differential association across the phenotypes tested. After family-wise error correction across all traits (FWERacross), an increased burden of singleton disruptive variants in the Regulome was associated with SCZ (FWERacross P=0.0339). The burden of singleton disruptive variants in the DISC1 Interactome was associated with low cognitive ability at age 11 (FWERacross P=0.0043). These results identify altered regulation of schizophrenia candidate genes by DISC1 and its core Interactome as an alternate pathway for schizophrenia risk, consistent with the emerging effects of rare copy number variants associated with intellectual disability.

Altered DNA methylation associated with a translocation linked to major mental illness

Recent work has highlighted a possible role for altered epigenetic modifications, including differential DNA methylation, in susceptibility to psychiatric illness. Here, we investigate blood-based DNA methylation in a large family where a balanced translocation between chromosomes 1 and 11 shows genome-wide significant linkage to psychiatric illness. Genome-wide DNA methylation was profiled in whole-blood-derived DNA from 41 individuals using the Infinium HumanMethylation450 BeadChip (Illumina Inc., San Diego, CA). We found significant differences in DNA methylation when translocation carriers (n = 17) were compared to related non-carriers (n = 24) at 13 loci. All but one of the 13 significant differentially methylated positions (DMPs) mapped to the regions surrounding the translocation breakpoints. Methylation levels of five DMPs were associated with genotype at SNPs in linkage disequilibrium with the translocation. Two of the five genes harbouring significant DMPs, DISC1 and DUSP10, have been previously shown to be differentially methylated in schizophrenia. Gene Ontology analysis revealed enrichment for terms relating to neuronal function and neurodevelopment among the genes harbouring the most significant DMPs. Differentially methylated region (DMR) analysis highlighted a number of genes from the MHC region, which has been implicated in psychiatric illness previously through genetic studies. We show that inheritance of a translocation linked to major mental illness is associated with differential DNA methylation at loci implicated in neuronal development/function and in psychiatric illness. As genomic rearrangements are over-represented in individuals with psychiatric illness, such analyses may be valuable more widely in the study of these conditions.

Regulation of mitochondrial dynamics by DISC1, a putative risk factor for major mental illness

Mitochondria are dynamic organelles that are essential to power the process of neurotransmission. Neurons must therefore ensure that mitochondria maintain their functional integrity and are efficiently transported along the full extent of the axons and dendrites, from soma to synapses. Mitochondrial dynamics (trafficking, fission and fusion) co-ordinately regulate mitochondrial quality control and function. DISC1 is a component of the mitochondrial transport machinery and regulates mitochondrial dynamics. DISC1's role in this is adversely affected by sequence variants connected to brain structure/function and disease risk, and by mutant truncation. The DISC1 interactors NDE1 and GSK3β are also involved, indicating a convergence of putative risk factors for psychiatric illness upon mitochondrial dynamics.

Altered Disrupted-in-Schizophrenia-1 Function Affects the Development of Cortical Parvalbumin Interneurons by an Indirect Mechanism

Disrupted-in-Schizophrenia-1 (DISC1) gene has been linked to schizophrenia and related major mental illness. Mouse Disc1 has been implicated in brain development, mainly in the proliferation, differentiation, lamination, neurite outgrowth and synapse formation and maintenance of cortical excitatory neurons. Here, the effects of two loss-of-function point mutations in the mouse Disc1 sequence (Q31L and L100P) on cortical inhibitory interneurons were investigated. None of the mutations affected the overall number of interneurons. However, the 100P, but not the 31L, mutation resulted in a significant decrease in the numbers of interneurons expressing parvalbumin mRNA and protein across the sensory cortex. To investigate role of Disc1 in regulation of parvalbumin expression, mouse wild-type Disc-1 or the 100P mutant form were electroporated in utero into cortical excitatory neurons. Overexpression of wild-type Disc1 in these cells caused increased densities of parvalbumin-expressing interneurons in the electroporated area and in areas connected with it, whereas expression of Disc1-100P did not. We conclude that the 100P mutation prevents expression of parvalbumin by a normally sized cohort of interneurons and that altering Disc1 function in cortical excitatory neurons indirectly affects parvalbumin expression by cortical interneurons, perhaps as a result of altered functional input from the excitatory neurons.

NDE1 and GSK3β Associate with TRAK1 and Regulate Axonal Mitochondrial Motility: Identification of Cyclic AMP as a Novel Modulator of Axonal Mitochondrial Trafficking

Mitochondria are essential for neuronal function, providing the energy required to power neurotransmission, and fulfilling many important additional roles. In neurons, mitochondria must be efficiently transported to sites, including synapses, where their functions are required. Neurons, with their highly elongated morphology, are consequently extremely sensitive to defective mitochondrial trafficking which can lead to neuronal ill-health/death. We recently demonstrated that DISC1 associates with mitochondrial trafficking complexes where it associates with the core kinesin and dynein adaptor molecule TRAK1. We now show that the DISC1 interactors NDE1 and GSK3β also associate robustly with TRAK1 and demonstrate that NDE1 promotes retrograde axonal mitochondrial movement. GSK3β is known to modulate axonal mitochondrial motility, although reports of its actual effect are conflicting. We show that, in our system, GSK3β promotes anterograde mitochondrial transport. Finally, we investigated the influence of cAMP elevation upon mitochondrial motility, and found a striking increase in mitochondrial motility and retrograde movement. DISC1, NDE1, and GSK3β are implicated as risk factors for major mental illness. Our demonstration that they function together within mitochondrial trafficking complexes suggests that defective mitochondrial transport may be a contributory disease mechanism in some cases of psychiatric disorder.

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.

DISC1 complexes with TRAK1 and Miro1 to modulate anterograde axonal mitochondrial trafficking

Disrupted-In-Schizophrenia 1 (DISC1) is a candidate risk factor for schizophrenia, bipolar disorder and severe recurrent depression. Here, we demonstrate that DISC1 associates robustly with trafficking-protein-Kinesin-binding-1 which is, in turn, known to interact with the outer mitochondrial membrane proteins Miro1/2, linking mitochondria to the kinesin motor for microtubule-based subcellular trafficking. DISC1 also associates with Miro1 and is thus a component of functional mitochondrial transport complexes. Consistent with these observations, in neuronal axons DISC1 promotes specifically anterograde mitochondrial transport. DISC1 thus participates directly in mitochondrial trafficking, which is essential for neural development and neurotransmission. Any factor affecting mitochondrial DISC1 function is hence likely to have deleterious consequences for the brain, potentially contributing to increased risk of psychiatric illness. Intriguingly, therefore, a rare putatively causal human DISC1 sequence variant, 37W, impairs the ability of DISC1 to promote anterograde mitochondrial transport. This is likely related to a number of mitochondrial abnormalities induced by expression of DISC1-37W, which redistributes mitochondrial DISC1 and enhances kinesin mitochondrial association, while also altering protein interactions within the mitochondrial transport complex.

DISC1 genetics, biology and psychiatric illness

Psychiatric disorders are highly heritable, and in many individuals likely arise from the combined effects of genes and the environment. A substantial body of evidence points towards DISC1 being one of the genes that influence risk of schizophrenia, bipolar disorder and depression, and functional studies of DISC1 consequently have the potential to reveal much about the pathways that lead to major mental illness. Here, we review the evidence that DISC1 influences disease risk through effects upon multiple critical pathways in the developing and adult brain.

The mitosis and neurodevelopment proteins NDE1 and NDEL1 form dimers, tetramers, and polymers with a folded back structure in solution

Paralogs NDE1 (nuclear distribution element 1) and NDEL1 (NDE-like 1) are essential for mitosis and neurodevelopment. Both proteins are predicted to have similar structures, based upon high sequence similarity, and they co-complex in mammalian cells. X-ray diffraction studies and homology modeling suggest that their N-terminal regions (residues 8-167) adopt continuous, extended α-helical coiled-coil structures, but no experimentally derived information on the structure of their C-terminal regions or the architecture of the full-length proteins is available. In the case of NDE1, no biophysical data exists. Here we characterize the structural architecture of both full-length proteins utilizing negative stain electron microscopy along with our established paradigm of chemical cross-linking followed by tryptic digestion, mass spectrometry, and database searching, which we enhance using isotope labeling for mixed NDE1-NDEL1. We determined that full-length NDE1 forms needle-like dimers and tetramers in solution, similar to crystal structures of NDEL1, as well as chain-like end-to-end polymers. The C-terminal domain of each protein, required for interaction with key protein partners dynein and DISC1 (disrupted-in-schizophrenia 1), includes a predicted disordered region that allows a bent back structure. This facilitates interaction of the C-terminal region with the N-terminal coiled-coil domain and is in agreement with previous results showing N- and C-terminal regions of NDEL1 and NDE1 cooperating in dynein interaction. It sheds light on recently identified mutations in the NDE1 gene that cause truncation of the encoded protein. Additionally, analysis of mixed NDE1-NDEL1 complexes demonstrates that NDE1 and NDEL1 can interact directly.

A t(1;11) translocation linked to schizophrenia and affective disorders gives rise to aberrant chimeric DISC1 transcripts that encode structurally altered, deleterious mitochondrial proteins

Disrupted-In-Schizophrenia 1 (DISC1) was identified as a risk factor for psychiatric illness through its disruption by a balanced chromosomal translocation, t(1;11)(q42.1;q14.3), that co-segregates with schizophrenia, bipolar disorder and depression. We previously reported that the translocation reduces DISC1 expression, consistent with a haploinsufficiency disease model. Here we report that, in lymphoblastoid cell lines, the translocation additionally results in the production of abnormal transcripts due to the fusion of DISC1 with a disrupted gene on chromosome 11 (DISC1FP1/Boymaw). These chimeric transcripts encode abnormal proteins, designated CP1, CP60 and CP69, consisting of DISC1 amino acids 1-597 plus 1, 60 or 69 amino acids, respectively. The novel 69 amino acids in CP69 induce increased α-helical content and formation of large stable protein assemblies. The same is predicted for CP60. Both CP60 and CP69 exhibit profoundly altered functional properties within cell lines and neurons. Both are predominantly targeted to mitochondria, where they induce clustering and loss of membrane potential, indicative of severe mitochondrial dysfunction. There is currently no access to neural material from translocation carriers to confirm these findings, but there is no reason to suppose that these chimeric transcripts will not also be expressed in the brain. There is thus potential for the production of abnormal chimeric proteins in the brains of translocation carriers, although at substantially lower levels than for native DISC1. The mechanism by which inheritance of the translocation increases risk of psychiatric illness may therefore involve both DISC1 haploinsufficiency and mitochondrial deficiency due to the effects of abnormal chimeric protein expression. GenBank accession numbers: DISC1FP1 (EU302123), Boymaw (GU134617), der 11 chimeric transcript DISC1FP1 exon 2 to DISC1 exon 9 (JQ650115), der 1 chimeric transcript DISC1 exon 4 to DISC1FP1 exon 4 (JQ650116), der 1 chimeric transcript DISC1 exon 6 to DISC1FP1 exon 3a (JQ650117).

DISC1 variants 37W and 607F disrupt its nuclear targeting and regulatory role in ATF4-mediated transcription

Disrupted-In-Schizophrenia 1 (DISC1), a strong genetic candidate for psychiatric illness, encodes a multicompartmentalized molecular scaffold that regulates interacting proteins with key roles in neurodevelopment and plasticity. Missense DISC1 variants are associated with the risk of mental illness and with brain abnormalities in healthy carriers, but the underlying mechanisms are unclear. We examined the effect of rare and common DISC1 amino acid substitutions on subcellular targeting. We report that both the rare putatively causal variant 37W and the common variant 607F independently disrupt DISC1 nuclear targeting in a dominant-negative fashion, predicting that DISC1 nuclear expression is impaired in 37W and 607F carriers. In the nucleus, DISC1 interacts with the transcription factor Activating Transcription Factor 4 (ATF4), which is involved in the regulation of cellular stress responses, emotional behaviour and memory consolidation. At basal cAMP levels, wild-type DISC1 inhibits the transcriptional activity of ATF4, an effect that is weakened by both 37W and 607F independently, most likely as a consequence of their defective nuclear targeting. The common variant 607F additionally reduces DISC1/ATF4 interaction, which likely contributes to its weakened inhibitory effect. We also demonstrate that DISC1 modulates transcriptional responses to endoplasmic reticulum stress, and that this modulatory effect is ablated by 37W and 607F. By showing that DISC1 amino acid substitutions associated with psychiatric illness affect its regulatory function in ATF4-mediated transcription, our study highlights a potential mechanism by which these variants may impact on transcriptional events mediating cognition, emotional reactivity and stress responses, all processes of direct relevance to psychiatric illness.

DISC1 at 10: connecting psychiatric genetics and neuroscience

Psychiatric genetics research, as exemplified by the DISC1 gene, aspires to inform on mental health etiology and to suggest improved strategies for intervention. DISC1 was discovered in 2000 through the molecular cloning of a chromosomal translocation that segregated with a spectrum of major mental illnesses in a single large Scottish family. Through in vitro experiments and mouse models, DISC1 has been firmly established as a genetic risk factor for a spectrum of psychiatric illness. As a consequence of its protein scaffold function, the DISC1 protein impacts on many aspects of brain function, including neurosignaling and neurodevelopment. DISC1 is a pathfinder for understanding psychopathology, brain development, signaling and circuitry. Although much remains to be learnt and understood, potential targets for drug development are starting to emerge, and in this review, we will discuss the 10 years of research that has helped us understand key roles of DISC1 in psychiatric disease.

NDE1 and NDEL1: multimerisation, alternate splicing and DISC1 interaction

Nuclear Distribution Factor E Homolog 1 (NDE1) and NDE-Like 1 (NDEL1) are highly homologous mammalian proteins. However, whereas NDEL1 is well studied, there is remarkably little known about NDE1. We demonstrate the presence of multiple isoforms of both NDE1 and NDEL1 in the brain, showing that NDE1 binds directly to multiple isoforms of Disrupted in Schizophrenia 1 (DISC1), and to itself. We also show that NDE1 can complex with NDEL1. Together these results predict a high degree of complexity of DISC1-mediated regulation of neuronal activity.

DISC1, PDE4B, and NDE1 at the centrosome and synapse

Disrupted-In-Schizophrenia 1 (DISC1) is a risk factor for schizophrenia and other major mental illnesses. Its protein binding partners include the Nuclear Distribution Factor E Homologs (NDE1 and NDEL1), LIS1, and phosphodiesterases 4B and 4D (PDE4B and PDE4D). We demonstrate that NDE1, NDEL1 and LIS1, together with their binding partner dynein, associate with DISC1, PDE4B and PDE4D within the cell, and provide evidence that this complex is present at the centrosome. LIS1 and NDEL1 have been previously suggested to be synaptic, and we now demonstrate localisation of DISC1, NDE1, and PDE4B at synapses in cultured neurons. NDE1 is phosphorylated by cAMP-dependant Protein Kinase A (PKA), whose activity is, in turn, regulated by the cAMP hydrolysis activity of phosphodiesterases, including PDE4. We propose that DISC1 acts as an assembly scaffold for all of these proteins and that the NDE1/NDEL1/LIS1/dynein complex is modulated by cAMP levels via PKA and PDE4.

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.

Disrupted in schizophrenia 1 and phosphodiesterase 4B: towards an understanding of psychiatric illness

Disrupted in schizophrenia 1 (DISC1) is one of the most convincing genetic risk factors for major mental illness identified to date. DISC1 interacts directly with phosphodiesterase 4B (PDE4B), an independently identified risk factor for schizophrenia. DISC1-PDE4B complexes are therefore likely to be involved in molecular mechanisms underlying psychiatric illness. PDE4B hydrolyses cAMP and DISC1 may regulate cAMP signalling through modulating PDE4B activity. There is evidence that expression of both genes is altered in some psychiatric patients. Moreover, DISC1 missense mutations that give rise to phenotypes related to schizophrenia and depression in mice are located within binding sites for PDE4B. These mutations reduce the association between DISC1 and PDE4B, and one results in reduced brain PDE4B activity. Altered DISC1-PDE4B interaction may thus underlie the symptoms of some cases of schizophrenia and depression. Factors likely to influence this interaction include expression levels, binding site affinities and the DISC1 and PDE4 isoforms involved. DISC1 and PDE4 isoforms are targeted to specific subcellular locations which may contribute to the compartmentalization of cAMP signalling. Dysregulated cAMP signalling in specific cellular compartments may therefore be a predisposing factor for major mental illness.

Isoform-selective susceptibility of DISC1/phosphodiesterase-4 complexes to dissociation by elevated intracellular cAMP levels

Disrupted-in-schizophrenia 1 (DISC1) is a genetic susceptibility factor for schizophrenia and related severe psychiatric conditions. DISC1 is a multifunctional scaffold protein that is able to interact with several proteins, including the independently identified schizophrenia risk factor phosphodiesterase-4B (PDE4B). Here we report that the 100 kDa full-length DISC1 isoform (fl-DISC1) can bind members of each of the four gene, cAMP-specific PDE4 family. Elevation of intracellular cAMP levels, so as to activate protein kinase A, caused the release of PDE4D3 and PDE4C2 isoforms from fl-DISC1 while not affecting binding of PDE4B1 and PDE4A5 isoforms. Using a peptide array strategy, we show that PDE4D3 binds fl-DISC1 through two regions found in common with PDE4B isoforms, the interaction of which is supplemented because of the presence of additional PDE4B-specific binding sites. We propose that the additional binding sites found in PDE4B1 underpin its resistance to release during cAMP elevation. We identify, for the first time, a functional distinction between the 100 kDa long DISC1 isoform and the short 71 kDa isoform. Thus, changes in the expression pattern of DISC1 and PDE4 isoforms offers a means to reprogram their interaction and to determine whether the PDE4 sequestered by DISC1 is released after cAMP elevation. The PDE4B-specific binding sites encompass point mutations in mouse Disc1 that confer phenotypes related to schizophrenia and depression and that affect binding to PDE4B. Thus, genetic variation in DISC1 and PDE4 that influence either isoform expression or docking site functioning may directly affect psychopathology.

Behavioral phenotypes of Disc1 missense mutations in mice

To support the role of DISC1 in human psychiatric disorders, we identified and analyzed two independently derived ENU-induced mutations in Exon 2 of mouse Disc1. Mice with mutation Q31L showed depressive-like behavior with deficits in the forced swim test and other measures that were reversed by the antidepressant bupropion, but not by rolipram, a phosphodiesterase-4 (PDE4) inhibitor. In contrast, L100P mutant mice exhibited schizophrenic-like behavior, with profound deficits in prepulse inhibition and latent inhibition that were reversed by antipsychotic treatment. Both mutant DISC1 proteins exhibited reduced binding to the known DISC1 binding partner PDE4B. Q31L mutants had lower PDE4B activity, consistent with their resistance to rolipram, suggesting decreased PDE4 activity as a contributory factor in depression. This study demonstrates that Disc1 missense mutations in mice give rise to phenotypes related to depression and schizophrenia, thus supporting the role of DISC1 in major mental illness.

Role of DISC1 in neural development and schizophrenia

How can we hope to explain mechanistically the schizophrenic phenotype? Perhaps through the reductionist approach of genetics, which is beginning to yield biological clues. Growing evidence supports the view that the well-established genetic risk factor DISC1 plays an important role in schizophrenia biology by interacting with FEZ1 and NDEL1 during neurodevelopment and with the phosphodiesterase PDE4B in neuronal cell signalling. Thus, DISC1 and its pathways support the neurodevelopmental hypothesis of schizophrenia and provide a mechanistic explanation for the characteristic cognitive deficits. Genetic variants of DISC1 also predispose to related affective (mood) disorders. As a consequence, we can speculate on the mechanisms of DISC1 action and possible routes to treatment for these common, debilitating brain disorders.

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.

Disrupted in schizophrenia 1: building brains and memories

Schizophrenia and bipolar affective disorder are common, debilitating, and poorly understood and treated disorders. Both conditions are highly heritable. Recent genetic studies have suggested that the gene disrupted in schizophrenia 1 (DISC1) is an important risk factor. DISC1 seems to have a key role in building the brain and memories by interacting with other proteins, including nuclear distribution E-like protein and phosphodiesterase 4B. Here, we review the current knowledge, highlight some key unanswered questions and propose ways forward towards a better understanding of normal and abnormal brain development and function. In the long term, this might lead to the discovery of drugs that are more efficacious and safer than currently available ones.

Disrupted In Schizophrenia 1 (DISC1): Subcellular targeting and induction of ring mitochondria

Several independent studies have identified Disrupted In Schizophrenia 1 (DISC1) as a potential susceptibility factor in the pathogenesis of schizophrenia and severe recurrent major depression. To identify potential mechanisms by which DISC1 may influence development of psychiatric illness, we investigated the cellular consequences of recombinant DISC1 expression in COS-7 cells. We show that the N-terminal head domain is sufficient for DISC1 mitochondrial and nuclear targeting, while sequence from the C-terminus facilitates centrosomal association. Loss of C-terminal sequence alters DISC1 subcellular distribution, significantly increasing nuclear localization. DISC1 over-expression produces striking mitochondrial reorganization in some cells, with formation of mitochondrial ring-like structures, indicating a potential involvement of DISC1 in mitochondrial fusion and/or fission.

DISC1 and PDE4B are interacting genetic factors in schizophrenia that regulate cAMP signaling

The disrupted in schizophrenia 1 (DISC1) gene is a candidate susceptibility factor for schizophrenia, but its mechanistic role in the disorder is unknown. Here we report that the gene encoding phosphodiesterase 4B (PDE4B) is disrupted by a balanced translocation in a subject diagnosed with schizophrenia and a relative with chronic psychiatric illness. The PDEs inactivate adenosine 3',5'-monophosphate (cAMP), a second messenger implicated in learning, memory, and mood. We show that DISC1 interacts with the UCR2 domain of PDE4B and that elevation of cellular cAMP leads to dissociation of PDE4B from DISC1 and an increase in PDE4B activity. We propose a mechanistic model whereby DISC1 sequesters PDE4B in resting cells and releases it in an activated state in response to elevated cAMP.

Association between the TRAX/DISC locus and both bipolar disorder and schizophrenia in the Scottish population

The Translin-associated factor X/Disrupted in Schizophrenia 1 (TRAX/DISC) region was first implicated as a susceptibility locus for schizophrenia by analysis of a large Scottish family in which a t(1;11) translocation cosegregates with schizophrenia, bipolar disorder and recurrent major depression. We now report evidence for association between bipolar disorder and schizophrenia and this locus in the general Scottish population. A systematic study of linkage disequilibrium in a representative sample of the Scottish population was undertaken across the 510 kb of TRAX and DISC1. SNPs representing each haplotype block were selected for case-control association studies of both schizophrenia and bipolar disorder. Significant association with bipolar disorder in women P=0.00026 (P=0.0016 in men and women combined) was detected in a region of DISC1. This same region also showed nominally significant association with schizophrenia in both men and women combined, P=0.0056. Two further regions, one in TRAX and the second in DISC1, showed weaker evidence for sex-specific associations of individual haplotypes with bipolar disorder in men and women respectively, P<0.01. Only the association between bipolar women and DISC1 remained significant after correction for multiple testing. This result provides further supporting evidence for DISC1 as a susceptibility factor for both bipolar disorder and schizophrenia, consistent with the diagnoses in the original Scottish translocation family.

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

Disrupted in schizophrenia 1 (DISC1) has been identified as a putative risk factor for schizophrenia and affective disorders through study of a Scottish family with a balanced (1;11) (q42.1;q14.3) translocation, which results in the disruption of the DISC1 locus and cosegregates with major psychiatric disease. Several other reports of genetic linkage and association between DISC1 and schizophrenia in a range of patient populations have added credibility to the DISC1-schizophrenia theory, but the function of the DISC1 protein is still poorly understood. Recent studies have suggested that DISC1 plays a role in neuronal outgrowth, possibly through reported interactions with the molecules Nudel and FEZ1. Here we have analyzed the DISC1 protein sequence to identify previously unknown regions that are important for the correct targeting of the protein and conducted imaging studies to identify DISC1 subcellular location. We have identified a central coiled-coil region and show it is critical for the subcellular targeting of DISC1. This domain is independent from the C-terminal Nudel binding domain highlighting the multidomain nature/functionality of the DISC1 protein. Furthermore, we have been able to provide the first direct evidence that DISC1 is localized to mitochondria in cultured cortical neurons that are dependent on an intact cytoskeleton. Surprisingly, Nudel is seen to differentially associate with mitochondrial markers in comparison to DISC1. Disruption of the cytoskeleton results in colocalization of Nudel and mitochondrial markers-the first observation of such a direct relationship. Mitochondrial dysfunction has been implicated to play a role in schizophrenia so we speculate that mutations in DISC1 or Nudel may impair mitochondrial transport or function, initiating a cascade of events culminating in psychiatric illness.

Cytogenetics and gene discovery in psychiatric disorders

The disruption of genes by balanced translocations and other rare germline chromosomal abnormalities has played an important part in the discovery of many common Mendelian disorder genes, somatic oncogenes and tumour supressors. A search of published literature has identified 15 genes whose genomic sequences are directly disrupted by translocation breakpoints in individuals with neuropsychiatric illness. In these cases, it is reasonable to hypothesise that haploinsufficiency is a major factor contributing to illness. These findings suggest that the predicted polygenic nature of psychiatric illness may not represent the complete picture; genes of large individual effect appear to exist. Cytogenetic events may provide important insights into neurochemical pathways and cellular processes critical for the development of complex psychiatric phenotypes in the population at large.

A genome scan and follow-up study identify a bipolar disorder susceptibility locus on chromosome 1q42

In this study, we report a genome scan for psychiatric disease susceptibility loci in 13 Scottish families. We follow up one of the linkage peaks on chromosome 1q in a substantially larger sample of 22 families affected by schizophrenia (SCZ) or bipolar affective disorder (BPAD). To minimise the effect of genetic heterogeneity, we collected mainly large extended families (average family size >18). The families collected were Scottish, carried no chromosomal abnormalities and were unrelated to the large family previously reported as segregating a balanced (1:11) translocation with major psychiatric disease. In the genome scan, we found linkage peaks with logarithm of odds (LOD) scores >1.5 on chromosomes 1q (BPAD), 3p (SCZ), 8p (SCZ), 8q (BPAD), 9q (BPAD) and 19q (SCZ). In the follow-up sample, we obtained most evidence for linkage to 1q42 in bipolar families, with a maximum (parametric) LOD of 2.63 at D1S103. Multipoint variance components linkage gave a maximum LOD of 2.77 (overall maximum LOD 2.47 after correction for multiple tests), 12 cM from the previously identified SCZ susceptibility locus DISC1. Interestingly, there was negligible evidence for linkage to 1q42 in the SCZ families. These results, together with results from a number of other recent studies, stress the importance of the 1q42 region in susceptibility to both BPAD and SCZ.

Disrupted in Schizophrenia 1 (DISC1) is a multicompartmentalized protein that predominantly localizes to mitochondria

DISC1 is disrupted by a chromosomal translocation cosegregating with schizophrenia and recurrent major depression in a large Scottish family and has also been reported as a potential susceptibility locus in independent populations. We reveal a widespread and complex pattern of DISC1 expression, with at least five forms of Disrupted in Schizophrenia 1 DISC1 detectable. Mitochondria are the predominant site of DISC1 expression with additional nuclear, cytoplasmic, and actin-associated locations evident. Although the subcellular targeting of DISC1 is clearly complex, the association with mitochondria is of interest as many mitochondrial deficits have been reported in schizophrenia and other neuropsychiatric illnesses. Moreover, of the many cellular functions performed by mitochondria, their role in oxidative phosphorylation, calcium homeostasis, and apoptosis may hold particular relevance for the neuronal disturbances believed to be involved in the pathogenesis of schizophrenia.

Yeast two-hybrid screens implicate DISC1 in brain development and function

DISC1 is a candidate gene for involvement in the aetiology of major psychiatric illnesses including schizophrenia. We report here the results of DISC1 yeast two-hybrid screens using human foetal and adult brain libraries. Twenty-one proteins from a variety of subcellular locations were identified, consistent with observations that DISC1 occupies multiple subcellular compartments. The cellular roles of the proteins identified implicate DISC1 in several aspects of central nervous system development and function, including gene transcription, mitochondrial function, modulation of the actin cytoskeleton, neuronal migration, glutamate transmission, and signal transduction. Intriguingly, mutations in one of the proteins identified, WKL1, have been previously suggested to underlie the aetiology of catatonic schizophrenia.

DISC1 and DISC2: discovering and dissecting molecular mechanisms underlying psychiatric illness

A balanced (1;11)(q42;q14) translocation co-segregates with schizophrenia and major affective disorders in a large Scottish family. The translocation breakpoint on chromosome 1 is located within the Disrupted in Schizophrenia 1 and 2 genes (DISC1 and DISC2). Consequently loss of normal function of these genes is likely to underlie the susceptibility to developing psychiatric disorders that is conferred by inheritance of the translocation. Additionally, a number of independent genetic studies highlight the region of chromosome 1q containing DISC1 and DISC2 as a likely susceptibility locus for both schizophrenia and affective disorders. These genes are thus implicated in the aetiology of major psychiatric disorders in several populations. Although the function of DISC1 was initially unknown, several recent reports have made significant progress towards understanding its role in the central nervous system. Intriguingly, all data obtained to date point towards an involvement in processes critical to neurodevelopment and function. DISC2 has not been studied in detail, but is likely to modulate DISC1 expression. Overall, it is clear from the combination of genetic and functional data that DISC1 and/or DISC2 are emerging as important factors in the molecular genetics of psychiatric illness.

Evolutionary constraints on the Disrupted in Schizophrenia locus

The Disrupted in Schizophrenia (DISC) locus on human chromosome 1q42 has been strongly implicated by genetic studies as a susceptibility locus for major mental illnesses. In humans the locus is transcriptionally complex, with multiple alternate splicing events, antisense transcription, and intergenic splicing all evident. We have compared the genomic sequence and transcription maps of this locus between human, mouse, pufferfish (Fugu rubripes), and, in part, zebrafish (Danio rerio). The order and orientation of EGLN1, TSNAX, and DISC1 genes are conserved between mammals and F. rubripes. Intergenic splicing and short intergenic transcripts are not found to be conserved features. DISC2, a putative noncoding transcript partially antisense to DISC1, is not conserved in mouse or F. rubripes. Alternate splice forms of the protein-coding DISC1 gene are conserved even though the genomic structure is not. The amino acid sequence of DISC1 is diverging rapidly, although a putative nuclear localization signal and discrete blocks of coiled coil are specifically conserved features.

Identification of polymorphisms within Disrupted in Schizophrenia 1 and Disrupted in Schizophrenia 2, and an investigation of their association with schizophrenia and bipolar affective disorder

We have undertaken a search for polymorphic sequence variation within Disrupted in Schizophrenia 1 and Disrupted in Schizophrenia 2 (DISC1 and DISC2), which are both novel genes that span a translocation breakpoint strongly associated with schizophrenia and related psychoses in a large Scottish family. A scan of the coding sequence, intron/exon boundaries, and part of the 5' and 3' untranslated regions of DISC1, plus 2.7 kb at the 3' end of DISC2, has revealed a novel microsatellite and 15 novel single nucleotide polymorphisms (SNPs). We have tracked the inheritance of four of the SNPs through multiply affected families, and carried out case-control association studies using the microsatellite and four common SNPs on populations of patients with schizophrenia or bipolar affective disorder versus normal control subjects. Neither co-segregation with disease status nor significant association was detected; however, we could not detect linkage disequilibrium between all these markers in the control population, arguing that an even greater density of informative markers is required to test rigorously for association in this genomic region.

Genomic structure and localisation within a linkage hotspot of Disrupted In Schizophrenia 1, a gene disrupted by a translocation segregating with schizophrenia

Two overlapping and antiparallel genes on chromosome 1, Disrupted In Schizophrenia 1 and 2 (DISC1 and DISC2), are disrupted by a (1;11)(q42.1;q14.3) translocation which segregates with schizophrenia through at least four generations of a large Scottish family. Consequently, these genes are worthy of further investigation as candidate genes potentially involved in the aetiology of major psychiatric illness. We have constructed a contiguous clone map of PACs and cosmids extending across at least 400 kb of the chromosome 1 translocation breakpoint region and this has provided the basis for examination of the genomic structure of DISC1. The gene consists of thirteen exons, estimated to extend across at least 300 kb of DNA. The antisense gene DISC2 overlaps with exon 9. Exon 11 contains an alternative splice site that removes 66 nucleotides from the open reading frame. The final intron of DISC1 belongs to the rare AT-AC class of introns. We have also mapped marker DIS251 in close proximity to DISC1, localising the gene within a critical region identified by several independent studies. Information regarding the structure of the DISC1 gene will facilitate assessment of its involvement in the aetiology of major mental illness in psychotic individuals unrelated to carriers of the translocation.

Chromosomal location and genomic structure of the human translin-associated factor X gene (TRAX; TSNAX) revealed by intergenic splicing to DISC1, a gene disrupted by a translocation segregating with schizophrenia

Two candidate genes, DISC1 and DISC2 on chromosome 1, are disrupted by a translocation that segregates with major psychiatric illness. Several DISC1 transcripts contain TRAX (HGMW-approved symbol TSNAX) sequence at the 5' end. These transcripts initiate at the 5' end of TRAX and terminate at the final exon of DISC1. Five species of transcript resulting from intergenic splicing have been identified; one encodes a novel TRAX/DISC1 fusion protein. The remaining four transcripts are bicistronic and encode a series of novel truncated isoforms of TRAX and DISC1. Demonstration that the various TRAX/DISC1 transcripts are translated awaits further experimentation. As a consequence of the observation of intergenic splicing, the human TRAX gene has been mapped at least 35 kb proximal to DISC1 and within approximately 150-250 kb of the translocation breakpoint at 1q42.1. The TRAX gene consists of six exons with a putative CpG island at the 5' end. Four major transcripts are produced from this gene, of which the smallest, at 2.7 kb, had previously been identified.

Disruption of two novel genes by a translocation co-segregating with schizophrenia

A balanced (1;11)(q42.1;q14.3) translocation segregates with schizophrenia and related psychiatric disorders in a large Scottish family (maximum LOD = 6.0). We hypothesize that the translocation is the causative event and that it directly disrupts gene function. We previously reported a dearth of genes in the breakpoint region of chromosome 11 and it is therefore unlikely that the expression of any genes on this chromosome has been affected by the translocation. By contrast, the corresponding region on chromosome 1 is gene dense and, not one, but two novel genes are directly disrupted by the translocation. These genes have been provisionally named Disrupted-In-Schizophrenia 1 and 2 ( DISC1 and DISC2 ). DISC1 encodes a large protein with no significant sequence homology to other known proteins. It is predicted to consist of a globular N-terminal domain(s) and helical C-terminal domain which has the potential to form a coiled-coil by interaction with another, as yet, unidentified protein(s). Similar structures are thought to be present in a variety of unrelated proteins that are known to function in the nervous system. The putative structure of the protein encoded by DISC1 is therefore compatible with a role in the nervous system. DISC2 apparently specifies a non-coding RNA molecule that is antisense to DISC1, an arrangement that has been observed at other loci where it is thought that the antisense RNA is involved in regulating expression of the sense gene. Altogether, these observations indicate that DISC1 and DISC2 should be considered formal candidate genes for susceptibility to psychiatric illness.

A long-range restriction map across 3 Mb of the chromosome 11 breakpoint region of a translocation linked to schizophrenia: localization of the breakpoint and the search for neighbouring genes

A balanced t(1;11)(q42.1;q14.3) translocation segregates with schizophrenia and related mental illness in a single large Scottish pedigree. We have constructed a long-range restriction map covering at least 3 Mb of the chromosome 11 breakpoint region and conducted searches for genes whose expression could be altered by the translocation, resulting in schizophrenia. Novel transcribed sequences of unknown function clustered around putative CpG islands, located approximately 500 kb and 700 kb above the breakpoint, represent the only evidence to date for expressed genes within the mapped region.

An allelic association study of two polymorphic markers in close proximity to a balanced translocation t(1:11) that co-segregates with mental illness

We report a case control association study using polymorphic markers D1S1621 and D11S931 in unrelated individuals with schizophrenia, unipolar depression and a matched control group. The two polymorphic markers were identified during the positional cloning of the translocation breakpoint t(1:11)(q43:q14.3) that cosegregates with schizophrenia and affective disorders. These markers provided an opportunity to investigate linkage disequilibrium with a postulated schizophrenia susceptibility gene close to the translocation breakpoint in random populations of schizophrenia and unipolar depression individuals compared with a normal control population. No significant differences between allele frequencies for either of the markers in the affected populations were observed in comparison with the control group, which provides evidence against a nearby gene of major effect in the populations studied.

DNA ligase I is required for fetal liver erythropoiesis but is not essential for mammalian cell viability

Four distinct DNA ligase activities (I-IV) have been identified within mammalian cells. Evidence has indicated that DNA ligase I is central to DNA replication, as well as being involved in DNA repair processes. A patient with altered DNA ligase I displayed a phenotype similar to Bloom's syndrome, being immunodeficient, growth retarded and predisposed to cancer. Fibroblasts isolated from this patient (46BR) exhibited abnormal lagging strand synthesis and repair deficiency. It has been reported that DNA ligase I is essential for cell viability, but here we show that cells lacking DNA ligase I are in fact viable. Using gene targeting in embryonic stem (ES) cells, we have produced DNA ligase I-deficient mice. Embryos develop normally to mid-term when haematopoiesis usually switches to the fetal liver. Thereupon acute anaemia develops, despite the presence of erythroid-committed progenitor cells in the liver. Thus DNA ligase I is required for normal development, but is not essential for replication. Hence a previously unsuspected redundancy must exist between mammalian DNA ligases.

Dental pantomography. The orthopantomograph: a method of patient positioning

The shape of the "in-focus" zone or focal trough given by the Orthopantomograph machine is shown. The anterior part of this zone is only 6 mm in thickness. The roots of the incisor teeth should, if possible, be placed accurately in this zone and a method of achieving this is suggested.

The chest film findings in 'Q' fever--a series of 35 cases

Thirty-five cases of 'Q' fever have been admitted and confirmed serologically over the past 20 years. Thirty-two of these cases had chest films on admission, and lung changes were present in 87%. The lung changes were: 1. Multiple round segmental consolidations, 5--10 cm in diameter, of ground glass density and usually situated in the lower lobes. 2. Linear atelectasis. 3. Lobar or partial lobar consolidation, with some loss of volume in the affected lobe. 4. A slight pleural reaction in a few cases. 5. Some cases had background emphysema of the lungs. All the lesions tended to be slow to clear. The resolution time was from 10 to 70 days, with an average time fo 30 days. Some of the segmental lesions became small, round and dense during resolution. The 35 cases were almost exclusively in males. The finding of a single or multiple round segmental opacities of ground glass density, as described, especially with linear atelectasis, was found to be good evidence that the patient had 'Q' fever. The point is made that the admission chest film is in some cases a very useful early pointer to the diagnosis. This allows specific chemotherapy to be started before the serological results have come back. Plate atelectasis was helpful as a distinguishing feature from primary atypical pneumonia.