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 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 obser-vations, in neuronal axons DISC1 promotes specifically anterogrademitochondrial transport. DISC1 thus parti-cipates directly inmitochondrial 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 humanDISC1 sequence variant, 37W, impairs the ability of DISC1 to promote anterogrademitochondrial transport. This is likely related toanumberofmitochondrial abnormalities inducedbyexpressionofDISC1-37W, which redistributes mitochondrial DISC1 and enhances kinesin mitochondrial association, while also altering protein interactions within the mitochondrial transport complex

PKA Phosphorylation of NDE1 Is DISC1/PDE4 Dependent and Modulates Its Interaction with LIS1 and NDEL1

Nuclear distribution factor E-homolog 1 (NDE1), Lissencephaly 1 (LIS1), and NDE-like 1 (NDEL1) together participate in essential neurodevelopmental processes, including neuronal precursor proliferation and differentiation, neuronal migration, and neurite out-growth. NDE1/LIS1/NDEL1 interacts with Disrupted in Schizophrenia 1 (DISC1) and the cAMP-hydrolyzing enzyme phosphodiesterase 4 (PDE4). DISC1, PDE4, NDE1, and NDEL1 have each been implicated as genetic risk factors for major mental illness. Here, we demonstrate that DISC1 and PDE4 modulate NDE1 phosphorylation by cAMP-dependent protein kinase A (PKA) and identify a novel PKA substrate site on NDE1 at threonine-131 (T131). Homology modeling predicts that phosphorylation at T131 modulates NDE1–LIS1 and NDE1–NDEL1 interactions, which we confirm experimentally. DISC1–PDE4 interaction thus modulates organization of the NDE1/NDEL1/LIS1 complex. T131-phosphorylated NDE1 is present at the postsynaptic density, in proximal axons, within the nucleus, and at the centrosome where it becomes substantially enriched during mitosis. Mutation of the NDE1 T131 site to mimic PKA phosphorylation inhibits neurite outgrowth. Thus PKA-dependent phosphorylation of the NDE1/LIS1/NDEL1 complex is DISC1–PDE4 modulated and likely to regulate its neural functions

SARS-CoV-2 RNA levels in Scotland’s wastewater

Nationwide, wastewater-based monitoring was newly established in Scotland to track the levels of SARS-CoV-2 viral RNA shed into the sewage network, during the COVID-19 pandemic. We present a curated, reference dataset produced by this national programme, from May 2020 to February 2022. Viral levels were analysed by RT-qPCR assays of the N1 gene, on RNA extracted from wastewater sampled at 162 locations. Locations were sampled up to four times per week, typically once or twice per week, and in response to local needs. We report sampling site locations with geographical coordinates, the total population in the catchment for each site, and the information necessary for data normalisation, such as the incoming wastewater flow values and ammonia concentration, when these were available. The methodology for viral quantification and data analysis is briefly described, with links to detailed protocols online. These wastewater data are contributing to estimates of disease prevalence and the viral reproduction number (R) in Scotland and in the UK

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

Disc1 variation leads to specific alterations in adult neurogenesis

Disrupted in schizophrenia 1 (DISC1) is a risk factor for a spectrum of neuropsychiatric illnesses including schizophrenia, bipolar disorder, and major depressive disorder. Here we use two missense Disc1 mouse mutants, described previously with distinct behavioural phenotypes, to demonstrate that Disc1 variation exerts differing effects on the formation of newly generated neurons in the adult hippocampus. Disc1 mice carrying a homozygous Q31L mutation, and displaying depressive-like phenotypes, have fewer proliferating cells while Disc1 mice with a homozygous L100P mutation that induces schizophrenia-like phenotypes, show changes in the generation, placement and maturation of newly generated neurons in the hippocampal dentate gyrus. Our results demonstrate Disc1 allele specific effects in the adult hippocampus, and suggest that the divergence in behavioural phenotypes may in part stem from changes in specific cell populations in the brain

Functional brain defects in a mouse model of a chromosomal t(1;11) translocation that disrupts DISC1 and confers increased risk of psychiatric illness

A balanced t(1;11) translocation that directly disrupts DISC1 is linked to schizophrenia and affective disorders. We previously showed that a mutant mouse, named Der1, recapitulates the effect of the translocation upon DISC1 expression. Here, RNAseq analysis of Der1 mouse brain tissue found enrichment for dysregulation of the same genes and molecular pathways as in neuron cultures generated previously from human t(1;11) translocation carriers via the induced pluripotent stem cell route. DISC1 disruption therefore apparently accounts for a substantial proportion of the effects of the t(1;11) translocation. RNAseq and pathway analysis of the mutant mouse predicts multiple Der1-induced alterations converging upon synapse function and plasticity. Synaptosome proteomics confirmed that the Der1 mutation impacts synapse composition, and electrophysiology found reduced AMPA:NMDA ratio in hippocampal neurons, indicating changed excitatory signalling. Moreover, hippocampal parvalbumin-positive interneuron density is increased, suggesting that the Der1 mutation affects inhibitory control of neuronal circuits. These phenotypes predict that neurotransmission is impacted at many levels by DISC1 disruption in human t(1;11) translocation carriers. Notably, genes implicated in schizophrenia, depression and bipolar disorder by large-scale genetic studies are enriched among the Der1-dysregulated genes, just as we previously observed for the t(1;11) translocation carrier-derived neurons. Furthermore, RNAseq analysis predicts that the Der1 mutation primarily targets a subset of cell types, pyramidal neurons and interneurons, previously shown to be vulnerable to the effects of common schizophrenia-associated genetic variants. In conclusion, DISC1 disruption by the t(1;11) translocation may contribute to the psychiatric disorders of translocation carriers through commonly affected pathways and processes in neurotransmission

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, impacting both neurosignalling and neurodevelopment. DISC1 is a pathfinder for understanding psychopathology, brain development, signaling and circuitry. Though 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

Expression of DISC1-Interactome Members Correlates with Cognitive Phenotypes Related to Schizophrenia

Cognitive dysfunction is central to the schizophrenia phenotype. Genetic and functional studies have implicated Disrupted-in-Schizophrenia 1 (DISC1), a leading candidate gene for schizophrenia and related psychiatric conditions, in cognitive function. Altered expression of DISC1 and DISC1-interactors has been identified in schizophrenia. Dysregulated expression of DISC1-interactome genes might, therefore, contribute to schizophrenia susceptibility via disruption of molecular systems required for normal cognitive function. Here, the blood RNA expression levels of DISC1 and DISC1-interacting proteins were measured in 63 control subjects. Cognitive function was assessed using neuropsychiatric tests and functional magnetic resonance imaging was used to assess the activity of prefrontal cortical regions during the N-back working memory task, which is abnormal in schizophrenia. Pairwise correlations between gene expression levels and the relationship between gene expression levels and cognitive function and N-back-elicited brain activity were assessed. Finally, the expression levels of DISC1, AKAP9, FEZ1, NDEL1 and PCM1 were compared between 63 controls and 69 schizophrenic subjects. We found that DISC1-interactome genes showed correlated expression in the blood of healthy individuals. The expression levels of several interactome members were correlated with cognitive performance and N-back-elicited activity in the prefrontal cortex. In addition, DISC1 and NDEL1 showed decreased expression in schizophrenic subjects compared to healthy controls. Our findings highlight the importance of the coordinated expression of DISC1-interactome genes for normal cognitive function and suggest that dysregulated DISC1 and NDEL1 expression might, in part, contribute to susceptibility for schizophrenia via disruption of prefrontal cortex-dependent cognitive functions

Altered Disrupted-in-Schizophrenia-1 function affects the development of cortical parvalbumin interneurons by an indirect mechanism.

<div><p><i>Disrupted-in-Schizophrenia-1 (DISC1)</i> 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 <i>Disc1</i> 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 <i>in utero</i> 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.</p></div