Following the discovery of the DISC1 gene in 2000, subsequent research has led to DISC1 becoming one of the most promising candidate genes for psychiatric disorders. Acting as a scaffold protein, DISC1 has a large number of interacting proteins and is involved in a series of intracellular signalling pathways. Amongst these binding proteins are two enzymes, PDE4 and GSK3β, that were originally implicated in psychiatric disease by virtue of their inhibition by psychoactive drugs. PDE4 enzymes are inhibited by rolipram, which possesses anti-depressant and anti-psychotic activity, while GSK3β is one of the major targets of lithium, a potent mood stabiliser. Both these enzymes are intricately involved in the PI3K/AKT, cAMP, and MAPK signalling pathways, all of which have a number of downstream outcomes with potential relevance to psychiatric disorders. The Millar and Porteous laboratory had established that DISC1 modulates PDE4 activity, but this predated awareness of GSK3 as another DISC1 interactor whose binding site overlapped with that of PDE4. Since cAMP is a key regulator of signalling pathways in the brain, I hypothesised that not only DISC1, but also GSK3β may be involved in the regulation of PDE4 activity to control local cAMP levels and gradients. To investigate this hypothesis, I characterised SHSY5Y cells as a model for measuring PDE4 activity, and performed a series of genetic and pharmacological manipulations on this system. Inhibition of GSK3β resulted in a decrease of basal PDE4 activity that was amplified by DISC1 overexpression. Wild type cells that were treated with forskolin exhibited a significant increase in PDE4 activity, which was suppressed by GSK3β inhibition and both overexpression and knockdown of DISC1. Further experiments confirmed that none of these changes were a result of differences in PDE4 mRNA or protein expression. Thus I have provided evidence that suggests tonic activation of PDE4 by GSK3β and evidence for modulation of PDE4 activity by DISC1. I provide evidence for the localisation of PDE4B & PDE4D with key psychiatric associated receptors in structures resembling developing dendritic spines; furthermore, agonism of NMDA receptors results in a significant increase in PDE4 activity in primary neurons. These results are a simple demonstration of an emerging principle in psychiatric research: that none of the signalling pathways implicated in psychiatric disease are acting in isolation. There are likely to be multiple points of integration between these pathways, with the demonstrated DISC1-GSK3β-PDE4 interaction forming one of these points. My results add an important new element to the understanding of how the DISC1 complex may regulate intracellular signalling in response to extracellular cues.

1H-Magnetic Resonance Spectroscopy (MRS) is a MRI paradigm that allows the levels of specific metabolites to be estimated in vivo [1]. This means that insights into the biochemical changes associated with a rare genetic change that raises the risk of mental disorders, and the impact of having a mental disorder, can potentially be made. In this study the levels of glutamate and N-acetyl-aspartate (NAA) were measured at 3T field strength in three separate voxels: right dorsolateral prefrontal cortex (DLPFC), left DLPFC and the anterior cingulate cortex (ACC). This thesis reports that members of a family that carry a unique t(1;11)(q42.2;q14) translocation that affects DISC1 have a substantially raised risk of developing a range of mental disorders, including bipolar affective disorder, schizophrenia and depression. A genetic change that leads to an increase in the susceptibility to a range of mental disorders is in line with other genetic studies that have been recently reported [2, 3]. The translocation was associated with a significant reduction in right DLPFC glutamate (mean difference= -2.11, CI= -0.24: -3.98, p=0.029) and left DLPFC NAA (mean difference= -1.97, CI= -0.34: -3.61, p=0.020). Changes in these metabolites offer some support to studies in cells and rodents trying to understand the impact of the t(1;11) translocation. More specifically the results offer support to studies that have linked alterations in DISC1's molecular biology to changes in glutamate receptors and mitochondrial function [4-6]. The results need to be interpreted with some caution due to the small sample size and the lack of a significant effect in the bilateral DLPFCs. People with a major mental disorder were also found to have significantly lower levels of glutamate in the left DLPFC (F=3.16, p=0.047). When compared to controls the reductions were significant in the people with a diagnosis of schizophrenia (mean difference= -0.86, CI= -0.19: -1.51, p=0.012), but not in people with bipolar affective disorder. Glutamate levels were significantly correlated with negative symptoms in people with schizophrenia (SANS r= -0.44, CI= -0.07: - 0.70, p= 0.024). The effect of experiencing depressive symptoms was also evaluated due to support for a link in previous studies [7, 8]. Whist the participants were not recruited due their experience of depressive symptoms, metabolite levels were found to be significantly associated with depressive symptoms in all participants with a mental disorder (all three voxels, both NAA and glutamate p < 0.05). The experience of depressive symptoms is not the same experiencing a depressive episode though, and further work may offer more insights into the association between metabolite changes and experience of depression. These findings provide insights into the relationship between diagnosis, current psychopathology and genetic risk in major mental disorders. The thesis provides some support that MRS imaging can be used to try understand neurobiological changes that are associated a genetic change, which is in turn linked to range of mental disorders. Interpreting the results of MRS imaging studies in humans remains challenging due to the complexity of the molecular biology that underpins the estimated metabolite levels, but where there has been a wide range of translational study into a specific protein (or genetic change) MRS may offer further information to help understand any effect in vivo.

Human pluripotent stem cell (hPSC)-derived neuronal and glial material presents a relatively new opportunity to model human neurophysiology in both health, and disease. Validation of regionally-defined hPSC-derived neurones and glia cultures thus represents the founding blocks of technology that aims to complement existing models. Principally, the relevance of in vitro hPSC-derived material is determined by how representative it is of native material, yet at present the physiology of these cells remains underexplored. Here, electrophysiology and pharmacology are used to functionally assess hPSC-derived excitatory cortical neurones (hECNs), motorneurones (MNs) and oligodendrocyte-lineage cells in the context of regional-specific properties and maturation. These properties are then examined in material derived from hPSCs generated from patients with neurological disorders. This thesis examines of the properties of GABAARs and strychnine-sensitive glycine receptors (GlyRs) in hECNs by assessing their subunit composition, and compares these with studies which have made comparable investigations of rodent tissue where maturation is associated with a shift in GABAA and GlyR compositions. Using pharmacology and RNAseq analysis, GABAAR and GlyRs in hECNs were found to possess receptor populations typical of those reported in the immature cortex. hECNs generated from patients harbouring a mutation to the Disrupted-in-schizophrenia-gene 1 (DISC1), a candidate schizophrenia gene, were then examined. Imbalances in the excitation/inhibition balance are suspected in schizophrenia and, in this regard, the intrinsic excitability properties alongside expression and composition of major neurotransmitter receptors and intracellular chloride concentration were assessed. No obvious differences in excitability or functional expression of AMPARs, GABAARs or NMDARs were observed between case and control derived neurones. Receptor composition and intracellular chloride concentrations were found to be predominantly immature-like, however, AMPAR composition and intracellular chloride concentration were found to be like that of adult cortical neurones. These data are discussed in the context of modelling DISC1-associated pathologies. Thirdly, MNs from hPSCs generated from ALS patients harbouring mutations on the C9ORF72 gene were examined. The hypothesis that increased glutamate-mediated excitoxicity could, in part, be explained by increased expression of Ca2+- permeable AMPARs was examined. The estimated mean single-channel conductance of AMPARs was found to be high in MNs derived from ALS patients, reminiscent of Ca2+-permeable AMPARs and was reversed by gene-editing of the C9ORF72 mutation. Finally, oligodendrocytes generated from ALS patients harbouring TARDBP mutations were examined. Distinctive electrophysiological shifts in oligodendrocytes-lineage cell development are reported. A similar AMPAR phenotype of elevated Ca2+-permeable AMPAR expression was observed in oligodendrocytes derived from two patient hPSC lines and was rescued in an isogenic, gene-edited line, raising the intriguing possibility of convergence in pathophysiologies in the nature of the overlap between cell-type, AMPAR pathology and excitotoxicity in ALS disease progression mechanisms.

In a large Scottish family a high incidence of schizophrenia, bipolar disorder and major depressive disorder co-segregates with a balanced autosomal translocation (t(1;11)(q42.1;q14.3). The translocation disrupts Disrupted-in-Schizophrenia-1 (DISC1) and DISC2 on chromosome 1, and DISC1FP1 (Disrupted-in-Schizophrenia-Fusion-Partner-1), also known as Boymaw, on chromosome 11. DISC1 is a leading candidate gene for major mental illness and is involved in neurodevelopment and cellular signalling, whilst DISC2 and DISC1FP1 are apparently non-coding RNA genes that undergo alternative splicing and that are expressed in the brain. This thesis aimed to investigate putative mechanisms of pathogenesis that may result from the t(1;11), with the hope that pathogenic mechanisms identified in the t(1;11) pedigree might shed light upon mechanisms conferring risk for psychiatric illness in the wider population. Previous work had identified DISC1/DISC1FP1 chimeric transcripts in t(1;11)-family derived lymphoblastoid cell lines. The detected transcripts include CP60 and CP69 which encode DISC1 aa1-597 plus an additional 60 or 69 amino acids from DISC1FP1, respectively. In this thesis a novel DISC1/DISC1FP1 transcript, CP1, was identified in t(1;11) lymphoblastoid cell lines. The CP1 transcript encodes DISC1 aa1-597 plus one glycine. A truncated form of DISC1 comprising aa1-597 was previously suggested to be a putative product of the translocation and, as such, has been the focus of multiple studies. The identification of the CP1 species is of interest as it differs from DISC1 aa1-597, by only a glycine. As glycines are simple uncharged aa’s, it is likely that these two DISC species share similar properties. In vitro exogenous expression of the three DISC1/DISC1FP1 protein species in both COS-7 and primary neuron cultures revealed contrasting cellular phenotypes. CP1 showed a diffuse cellular localisation pattern with cells containing readily visible tubular mitochondria. This is indistinguishable from the staining pattern of DISC1 aa1-597, highlighting the high degree of similarity between these species. CP60 and CP69, however, appeared to be clustered in the perinuclear region of the cell. Initial staining attempts with MitoTracker Red to visualise mitochondria in CP60 and CP69 expressing cells resulted in fewer than 30% of cells being stained. In those that did stain, the mitochondria appeared clustered. The absence of MitoTracker Red staining in mitochondria may be due to the loss of the mitochondrial membrane potential, Δψm. The adoption of a co-staining protocol with antibodies for mitochondrial proteins enabled the visualisation of mitochondrial structure in all of the cells exogenously expressing CP60 and CP69. All of these mitochondria possessed a clustered morphology, with which CP60 and CP69 expression was substantially co-localised. To see if MitoTracker staining was perturbed, in t(1;11) lymphoblastoid cell lines, as may occur if the DISC1/DISC1FP1 chimeras are expressed endogenously, the fluorescence of MitoTracker Red staining was investigated by FACS. Pooled analysis of experimental replicates revealed a negative result, with MitoTracker Red staining in t(1;11) lymphoblastoid cell lines not differing from controls. These findings indicate a need for further research using the mitochondrial membrane potential, Δψm as a metric as this would enable variations in mitochondrial mass to be accounted for. Prior to my arrival, an expression microarray had been carried out on lymphoblastoid cell line cDNA to assess gene expression differences resulting from the t(1;11). In order to identify putative pathogenic mechanisms, I carried out functional enrichment analysis of the expression array data using multiple analysis programs. Several programs detected dysregulation of the cell cycle and enrichment of altered expression of genes involved in the immune response and inflammation in t(1;11) carriers. The use of a rare variant investigative paradigm in this thesis furthers understanding of the putative pathogenic mechanisms that might act to increase risk for psychiatric illness in t(1;11) carriers. Moreover, it may aid the biological understanding of the aetiology of psychiatric illness in the general population. As such, improved understanding of the mechanisms of risk in the t(1;11) pedigree may eventually lead to the development of better treatments. In the intervening time since some of the research for thesis was published, two studies have emerged that may serve to highlight potential mechanisms of pathogenic action mediated by CP60 and CP69 expression. It has recently been observed that WT-DISC1 couples to the adaptor protein TRAK1 and the mitochondrial membrane anchor Miro1, which are part of the mitochondrial transport complex (Ogawa et al, 2014; Norkett et al, 2016). Furthermore, the exogenous expression of CP60 impairs bidirectional mitochondrial trafficking (Norkett et al, 2016). This suggests that CP60 expression may impair interactions with TRAK1 and Miro1. Given the sequence homology between CP60 and CP69, mitochondrial transport deficits also likely arise with CP69 expression. It is therefore possible that the exogenously expressed CP60 and CP69 proteins could be docked on stationary mitochondria, which may contribute to the clustered expression patterns observed.

Neurodevelopmental disorders (NDDs) are a heterogeneous set of disorders that are characterized by early disruptions to brain development and include autism spectrum disorder (ASD), attention deficit/hyperactivity disorder (ADHD), developmental delay (DD), intellectual disability (ID), epilepsy and schizophrenia (SZ). Although thousands of genetic risk variants have been identified, there is a lack of understanding of how they impact cellular and molecular mechanisms that underlie the clinical presentation and heterogeneity of NDDs. To investigate this, we used a combination of cellular, molecular, bioinformatic and omics methods to study NDD-associated molecular pathways in distinct neuronal populations. First, we studied the interaction between the high-confidence SZ risk genes DISC1 and NRG1-ErbB4 in cortical inhibitory neurons and found that NRG1-ErbB4 functions through DISC1 to regulate dendrite growth and excitatory synapses onto inhibitory neurons. Next, we studied the 15q13.3 microdeletion, a recurrent copy number variation (CNV) that is associated with multiple NDDs. Using a heterozygous mouse model [Df(h15q13)/+] and human sequencing data we identified OTUD7A (encoding a deubiquitinase) as an important gene driving neurodevelopmental phenotypes in the 15q13.3 microdeletion syndrome. Due to the paucity of literature on the function of OTUD7A in the brain, we used a proximity-labeling approach (BioID2) to elucidate the OTUD7A protein interaction network (PIN) in cortical neurons, and to examine how patient mutations affect the OTUD7A PIN. We found that the OTUD7A PIN was enriched for postsynaptic and axon initial segment proteins, and that distinct patient mutations have shared and distinct effects on the OTUD7A PIN. Further, we identified the interaction of OTUD7A with a high-confidence bipolar risk gene ANK3, which encodes AnkyrinG. We identified decreased levels of AnkyrinG in Df(h15q13)/+ neurons, and synaptic phenotypes were rescued by increasing AnkyrinG levels or targeting the Wnt pathway. Future investigation should include examination of the role of OTUD7A deubiquitinase activity in neural development. / Dissertation / Doctor of Philosophy (PhD) / Neurodevelopmental disorders result from disruptions to early brain development and include autism spectrum disorder (ASD), developmental delay (DD), epilepsy, and schizophrenia (SZ). These disorders affect more than 3% of children worldwide and can have a significant impact on an individual’s quality of life, including an increased risk of death in some cases. There is currently a lack of understanding of how these disorders develop and how to effectively treat them. Neurodevelopmental disorders are thought to arise from alterations in the connections between brain cells (neurons) and one of the major risk factors for these disorders is having certain variations in regions of the genome (DNA sequences), with more than 1000 of these risk variants having been identified so far. In this thesis, we analyzed how genetic risk factors interact in neurons to regulate neural connectivity. We discovered that risk variants found in individuals with different disorders actually work together to regulate similar processes important for neural connectivity, which suggests that distinct disorders may share a common underlying cause. Additionally, we established the importance of a new ASD risk gene and discovered that it interacts with other known risk genes to regulate neural connectivity. This thesis provides new insights into the processes in the brain that lead to neurodevelopmental disorders and has implications for future development of effective therapies for individuals affected by these disorders.

Schizophrenia is a mental illness with early adult onset. Prophylactic treatments would be clinically important and therefore we investigated the effect of two interventions: influenza vaccination of pregnant mothers and valproate treatment during late adolescence. Maternal immune response during pregnancy is thought to adversely affect brain development. We sought to assess whether immune activation by influenza vaccine could itself cause behavioural abnormalities in a mouse model. Our data suggest that further work is needed to make firm conclusions about the behavioural effects of the influenza vaccine. The second part of this thesis describes an analysis of valproate treatment on cortical neuron morphology in Disc1 L100P mice, a model for schizophrenia. Valproate was previously shown to prevent the onset of abnormal behaviours in Disc1 L100P mice. Contrary to expectations, valproate decreased apical spine density and the number of dendritic processes rather than reversing the dendritic deficits seen in Disc1 L100P mice.

Schizophrenia is a mental illness with early adult onset. Prophylactic treatments would be clinically important and therefore we investigated the effect of two interventions: influenza vaccination of pregnant mothers and valproate treatment during late adolescence. Maternal immune response during pregnancy is thought to adversely affect brain development. We sought to assess whether immune activation by influenza vaccine could itself cause behavioural abnormalities in a mouse model. Our data suggest that further work is needed to make firm conclusions about the behavioural effects of the influenza vaccine. The second part of this thesis describes an analysis of valproate treatment on cortical neuron morphology in Disc1 L100P mice, a model for schizophrenia. Valproate was previously shown to prevent the onset of abnormal behaviours in Disc1 L100P mice. Contrary to expectations, valproate decreased apical spine density and the number of dendritic processes rather than reversing the dendritic deficits seen in Disc1 L100P mice.

Bipolar disorder is a heritable psychiatric disorder, and several of the genes associated with bipolar disorder and related psychotic disorders are involved in the development and maintenance of white matter in the brain. Patients with bipolar disorder have an increased incidence of white matter hyper-intensities, and quantitative brain imaging studies collectively indicate subtle decreases in white matter density and integrity in bipolar patients. This suggests that genetic vulnerability to psychosis may manifest itself as reduced white matter integrity, and that white matter integrity is an endophenotype of bipolar disorder. This thesis comprises a series of studies designed to test the role of white matter in genetic risk to bipolar disorder by analysis of diffusion tensor imaging (DTI) data in the Bipolar Family Study. Various established analysis methods for DTI, including whole-brain voxel-based statistics, tract-based spatial statistics (TBSS) and probabilistic neighbourhood tractography, were applied with fractional anisotropy (FA) as the outcome measure. Widespread but subtle white matter integrity reductions were found in unaffected relatives of patients with bipolar disorder, whilst more localised reductions were associated with cyclothymic temperament. Next, the relation of white matter to four of the most prominent psychosis candidate genes, NRG1, ErbB4, DISC1 and ZNF804A, was investigated. A core haplotype in NRG1, and three of the four key single nucleotide polymorphisms (SNPs) within it, showed an association with FA in the anterior thalamic radiations and the uncinate fasciculi. For the three SNPs considered in ErbB4, results were inconclusive, but this was consistent with the background literature. Most notable however, was a clear association of a non-synonymous DISC1 SNP, Ser704Cys, with FA extending over most of the white matter in the TBSS and voxel-based analyses. Finally, FA was not associated with a genome-wide supported risk SNP in ZNF804A, a finding which could not be attributed to a lack of statistical power, and which contradicts a strong, but previously untested hypothesis. Whilst the above results need corroboration from independent studies, other studies are needed to address the cellular and molecular basis of these findings. Overall, this work provides strong support for the role of white matter integrity in genetic vulnerability to bipolar disorder and the wider psychosis spectrum and encourages its future use as an endophenotype.

The Disrupted-In-Schizophrenia 1 (DISC1) gene is one of the most established risk genes for psychiatric illness currently being studied, having originally been identified as being directly disrupted by a balanced chromosomal translocation that cosegregates with schizophrenia and other major mental illness a large Scottish family. The DISC1 protein is believed to act as a molecular scaffold within the cell, binding to a large number of other proteins. Three of these protein interactors, Phosphodiesterase 4B (PDE4B), Nuclear Distribution Factor E (Aspergillus nidulans)-homologue 1 (NDE1) and NDE-Like 1 (NDEL1) all have evidence implicating them as schizophrenia-related proteins in their own right. NDE1 and NDEL1 are highly similar proteins which are known to play cellular roles including microtubule function and mitosis. Their orthologues have also been shown to be important in neurodevelopment within the mouse brain. To date, most work in the literature has investigated NDEL1, with few focusing on NDE1. In the thesis, I first seek to establish a basic biology for NDE1 by the identification of splice variants expressed in the brain, establishing cellular localisation patterns within the cell and investigating NDE1 multimerisation. The relationship between NDE1 and NDEL1 is also investigated, with the two being found to form complexes together and to have partially over-lapping expression patterns within the cell. That NDE1 and DISC1 directly interact is confirmed. The relationship between NDE1 and PDE4B is then investigated, with the two proteins found to complex within the cell. Additionally, it is shown that NDE1 can be phosphorylated by protein kinase A (PKA). This kinase is cAMP dependant, and is thus indirectly regulated by the cAMP-degrading action of PDE4B protein. Attempts to map and analyse the effect of this phosphorylation on NDE1 are made.

Disrupted in schizophrenia 1 (DISC1), located on chromosome 1, was first identified due to its disruption by a chromosomal translocation, t(1;11)(q42;q14). This translocation co-segregates with psychiatric illness in the Scottish family within which it was discovered. DISC1 is a component of the mitochondrial trafficking machinery and regulates trafficking of mitochondria in neurons, possibly implicating defective mitochondrial trafficking as a contributory factor in psychiatric illness. The product of another candidate gene for psychiatric illness, Glycogen synthase kinase 3β (GSK3β), is known to interact directly with DISC1 and has also been reported to be involved in mitochondrial trafficking. The interaction of these proteins has not been investigated in this process. The work in this thesis centres around a novel mouse model of the t(1:11) translocation. I use time-lapse imaging of live cells to show that hippocampal neurons cultured from this mouse model exhibit altered axonal mitochondrial trafficking, including reduced mitochondrial pausing. I also demonstrate that the DISC1 interactor GSK3β is a component of the mitochondrial trafficking machinery and investigate effects of the t(1:11) event upon this multi-protein complex. Finally, I demonstrate altered mitochondrial motility responses to overexpression of GSK3β in mutant neurons. Defective mitochondrial trafficking, particularly reduced pausing, could result in an altered distribution of mitochondria within neurons, leading to an impaired ability to respond to cellular conditions, such as the requirement to power synaptic vesicle release or the ion pumps that restore membrane potential following action potential generation. This could ultimately affect neuron viability, leading to brain dysfunction. My data therefore support a proposed disease mechanism whereby defective mitochondrial trafficking contributes to susceptibility to psychiatric illness in carriers of the t(1:11) translocation, and may be relevant to psychiatric illness in general.