Schizophrenia susceptibility gene dysbindin regulates glutamatergic and dopaminergic functions via distinctive mechanisms in Drosophila

Pre-Pulse Inhibition of an escape response in adult fruit fly, Drosophila melanogaster

Pre-Pulse Inhibition (PPI) is a neural process where suppression of a startle response is elicited by preceding the startling stimulus (Pulse) with a weak, non-startling one (Pre-Pulse). Defective PPI is widely employed as a behavioural endophenotype in humans and mammalian disorder-relevant models for neuropsychiatric disorders. We have developed a user-friendly, semi-automated, high-throughput-compatible Drosophila light-off jump response PPI paradigm, with which we demonstrate that PPI, with similar parameters measured in mammals, exists in adults of this model organism. We report that Drosophila PPI is affected by reduced expression of Dysbindin and both reduced and increased expression of Nmdar1 (N-methyl-D-aspartate receptor 1), perturbations associated with schizophrenia. Studying the biology of PPI in an organism that offers a plethora of genetic tools and a complex and well characterized connectome will greatly facilitate our efforts to gain deeper insight into the aetiology of human mental disorders, while reducing the need for mammalian models.

Experimentally induced active and quiet sleep engage non-overlapping transcriptional programs in Drosophila

Sleep in mammals can be broadly classified into two different physiological categories: rapid eye movement (REM) sleep and slow-wave sleep (SWS), and accordingly REM and SWS are thought to achieve a different set of functions. The fruit fly Drosophila melanogaster is increasingly being used as a model to understand sleep functions, although it remains unclear if the fly brain also engages in different kinds of sleep as well. Here, we compare two commonly used approaches for studying sleep experimentally in Drosophila: optogenetic activation of sleep-promoting neurons and provision of a sleep-promoting drug, gaboxadol. We find that these different sleep-induction methods have similar effects on increasing sleep duration, but divergent effects on brain activity. Transcriptomic analysis reveals that drug-induced deep sleep ('quiet' sleep) mostly downregulates metabolism genes, whereas optogenetic 'active' sleep upregulates a wide range of genes relevant to normal waking functions. This suggests that optogenetics and pharmacological induction of sleep in Drosophila promote different features of sleep, which engage different sets of genes to achieve their respective functions.

Experimentally induced active and quiet sleep engage non-overlapping transcriptional programs in Drosophila

Sleep in mammals can be broadly classified into two different physiological categories: rapid eye movement (REM) sleep and slow wave sleep (SWS), and accordingly REM and SWS are thought to achieve a different set of functions. The fruit fly Drosophila melanogaster is increasingly being used as a model to understand sleep functions, although it remains unclear if the fly brain also engages in different kinds of sleep as well. Here, we compare two commonly used approaches for studying sleep experimentally in Drosophila: optogenetic activation of sleep-promoting neurons and provision of a sleep-promoting drug, Gaboxadol. We find that these different sleep-induction methods have similar effects on increasing sleep duration, but divergent effects on brain activity. Transcriptomic analysis reveals that drug-induced deep sleep ('quiet' sleep) mostly downregulates metabolism genes, whereas optogenetic 'active' sleep upregulates a wide range of genes relevant to normal waking functions. This suggests that optogenetics and pharmacological induction of sleep in Drosophila promote different features of sleep, which engage different sets of genes to achieve their respective functions.

Pallidin function in Drosophila surface glia regulates sleep and is dependent on amino acid availability

The Pallidin protein is a central subunit of a multimeric complex called biogenesis of lysosome-related organelles complex 1 (BLOC1) that regulates specific endosomal functions and has been linked to schizophrenia. We show here that downregulation of Pallidin and other members of BLOC1 in the surface glia, the Drosophila equivalent of the blood-brain barrier, reduces and delays nighttime sleep in a circadian-clock-dependent manner. In agreement with BLOC1 involvement in amino acid transport, downregulation of the large neutral amino acid transporter 1 (LAT1)-like transporters JhI-21 and mnd, as well as of TOR (target of rapamycin) amino acid signaling, phenocopy Pallidin knockdown. Furthermore, supplementing food with leucine normalizes the sleep/wake phenotypes of Pallidin downregulation, and we identify a role for Pallidin in the subcellular trafficking of JhI-21. Finally, we provide evidence that Pallidin in surface glia is required for GABAergic neuronal activity. These data identify a BLOC1 function linking essential amino acid availability and GABAergic sleep/wake regulation.

Dysbindin-1A modulation of astrocytic dopamine and basal ganglia dependent behaviors relevant to schizophrenia

The mechanisms underlying the dichotomic cortical/basal ganglia dopaminergic abnormalities in schizophrenia are unclear. Astrocytes are important non-neuronal modulators of brain circuits, but their role in dopaminergic system remains poorly explored. Microarray analyses, immunohistochemistry, and two-photon laser scanning microscopy revealed that Dys1 hypofunction increases the reactivity of astrocytes, which express only the Dys1A isoform. Notably, behavioral and electrochemical assessments in mice selectively lacking the Dys1A isoform unraveled a more prominent impact of Dys1A in behavioral and dopaminergic/D2 alterations related to basal ganglia, but not cortical functioning. Ex vivo electron microscopy and protein expression analyses indicated that selective Dys1A disruption might alter intracellular trafficking in astrocytes, but not in neurons. In agreement, Dys1A disruption only in astrocytes resulted in decreased motivation and sensorimotor gating deficits, increased astrocytic dopamine D2 receptors and decreased dopaminergic tone within basal ganglia. These processes might have clinical relevance because the caudate, but not the cortex, of patients with schizophrenia shows a reduction of the Dys1A isoform. Therefore, we started to show a hitherto unknown role for the Dys1A isoform in astrocytic-related modulation of basal ganglia behavioral and dopaminergic phenotypes, with relevance to schizophrenia.

Inter-Species Rescue of Mutant Phenotype-The Standard for Genetic Analysis of Human Genetic Disorders in Drosophila melanogaster Model

Drosophila melanogaster (the fruit fly) is arguably a superstar of genetics, an astonishing versatile experimental model which fueled no less than six Nobel prizes in medicine. Nowadays, an evolving research endeavor is to simulate and investigate human genetic diseases in the powerful D. melanogaster platform. Such a translational experimental strategy is expected to allow scientists not only to understand the molecular mechanisms of the respective disorders but also to alleviate or even cure them. In this regard, functional gene orthology should be initially confirmed in vivo by transferring human or vertebrate orthologous transgenes in specific mutant backgrounds of D. melanogaster. If such a transgene rescues, at least partially, the mutant phenotype, then it qualifies as a strong candidate for modeling the respective genetic disorder in the fruit fly. Herein, we review various examples of inter-species rescue of relevant mutant phenotypes of the fruit fly and discuss how these results recommend several human genes as candidates to study and validate genetic variants associated with human diseases. We also consider that a wider implementation of this evolutionist exploratory approach as a standard for the medicine of genetic disorders would allow this particular field of human health to advance at a faster pace.

The Drosophila ortholog of the schizophrenia-associated CACNA1A and CACNA1B voltage-gated calcium channels regulate memory, sleep and circadian rhythms

Schizophrenia exhibits up to 80% heritability. A number of genome wide association studies (GWAS) have repeatedly shown common variants in voltage-gated calcium (Ca_v) channel genes CACNA1C, CACNA1I and CACNA1G have a major contribution to the risk of the disease. More recently, studies using whole exome sequencing have also found that CACNA1B (Ca_v2.2 N-type) deletions and rare disruptive variants in CACNA1A (Ca_v2.1 P/Q-type) are associated with schizophrenia. The negative symptoms of schizophrenia include behavioural defects such as impaired memory, sleep and circadian rhythms. It is not known how variants in schizophrenia-associated genes contribute to cognitive and behavioural symptoms, thus hampering the development of treatment for schizophrenia symptoms. In order to address this knowledge gap, we studied behavioural phenotypes in a number of loss of function mutants for the Drosophila ortholog of the Ca_v2 gene family called cacophony (cac). cac mutants showed several behavioural features including decreased night-time sleep and hyperactivity similar to those reported in human patients. The change in timing of sleep-wake cycles suggested disrupted circadian rhythms, with the loss of night-time sleep being caused by loss of cac just in the circadian clock neurons. These animals also showed a reduction in rhythmic circadian behaviour a phenotype that also could be mapped to the central clock. Furthermore, reduction of cac just in the clock resulted in a lengthening of the 24 h period. In order to understand how loss of Ca_v2 function may lead to cognitive deficits and underlying cellular pathophysiology we targeted loss of function of cac to the memory centre of the fly, called the mushroom bodies (MB). This manipulation was sufficient to cause reduction in both short- and intermediate-term associative memory. Memory impairment was accompanied by a decrease in Ca²⁺ transients in response to a depolarizing stimulus, imaged in the MB presynaptic terminals. This work shows loss of cac Ca_v2 channel function alone causes a number of cognitive and behavioural deficits and underlying reduced neuronal Ca²⁺ transients, establishing Drosophila as a high-throughput in vivo genetic model to study the Ca_v channel pathophysiology related to schizophrenia.

Assessing olfactory, memory, social and circadian phenotypes associated with schizophrenia in a genetic model based on Rim

Schizophrenia shows high heritability and several of the genes associated with this disorder are involved in calcium (Ca2+) signalling and synaptic function. One of these is the Rab-3 interacting molecule-1 (RIM1), which has recently been associated with schizophrenia by Genome Wide Association Studies (GWAS). However, its contribution to the pathophysiology of this disorder remains unexplored. In this work, we use Drosophila mutants of the orthologue of RIM1, Rim, to model some aspects of the classical and non-classical symptoms of schizophrenia. Rim mutants showed several behavioural features relevant to schizophrenia including social distancing and altered olfactory processing. These defects were accompanied by reduced evoked Ca2+ influx and structural changes in the presynaptic terminals sent by the primary olfactory neurons to higher processing centres. In contrast, expression of Rim-RNAi in the mushroom bodies (MBs), the main memory centre in flies, spared learning and memory suggesting a differential role of Rim in different synapses. Circadian deficits have been reported in schizophrenia. We observed circadian locomotor activity deficits in Rim mutants, revealing a role of Rim in the pacemaker ventral lateral clock neurons (LNvs). These changes were accompanied by impaired day/night remodelling of dorsal terminal synapses from a subpopulation of LNvs and impaired day/night release of the circadian neuropeptide pigment dispersing factor (PDF) from these terminals. Lastly, treatment with the commonly used antipsychotic haloperidol rescued Rim locomotor deficits to wildtype. This work characterises the role of Rim in synaptic functions underlying behaviours disrupted in schizophrenia.

AANAT1 functions in astrocytes to regulate sleep homeostasis

How the brain controls the need and acquisition of recovery sleep after prolonged wakefulness is an important issue in sleep research. The monoamines serotonin and dopamine are key regulators of sleep in mammals and in Drosophila. We found that the enzyme arylalkylamine N-acetyltransferase 1 (AANAT1) is expressed by Drosophila astrocytes and specific subsets of neurons in the adult brain. AANAT1 acetylates monoamines and inactivates them, and we found that AANAT1 limited the accumulation of serotonin and dopamine in the brain upon sleep deprivation (SD). Loss of AANAT1 from astrocytes, but not from neurons, caused flies to increase their daytime recovery sleep following overnight SD. Together, these findings demonstrate a crucial role for AANAT1 and astrocytes in the regulation of monoamine bioavailability and homeostatic sleep.

Modelling Learning and Memory in Drosophila to Understand Intellectual Disabilities

Neurodevelopmental disorders (NDDs) include a large number of conditions such as Fragile  X  syndrome, autism spectrum disorders and Down syndrome, among others. They are characterized by limitations in adaptive and social behaviors, as well as intellectual disability (ID). Whole-exome and whole-genome sequencing studies have highlighted a large number of NDD/ID risk genes. To dissect the genetic causes and underlying biological pathways, in vivo experimental validation of the effects of these mutations is needed. The fruit fly, Drosophila melanogaster, is an ideal model to study NDDs, with highly tractable genetics, combined with simple behavioral and circuit assays, permitting rapid medium-throughput screening of NDD/ID risk genes. Here, we review studies where the use of well-established assays to study mechanisms of learning and memory in Drosophila has permitted insights into molecular mechanisms underlying IDs. We discuss how technologies in the fly model, combined with a high degree of molecular and physiological conservation between flies and mammals, highlight the Drosophila system as an ideal model to study neurodevelopmental disorders, from genetics to behavior.

Drosophila Glia: Models for Human Neurodevelopmental and Neurodegenerative Disorders

Glial cells are key players in the proper formation and maintenance of the nervous system, thus contributing to neuronal health and disease in humans. However, little is known about the molecular pathways that govern glia-neuron communications in the diseased brain. Drosophila provides a useful in vivo model to explore the conserved molecular details of glial cell biology and their contributions to brain function and disease susceptibility. Herein, we review recent studies that explore glial functions in normal neuronal development, along with Drosophila models that seek to identify the pathological implications of glial defects in the context of various central nervous system disorders.

The behavioral and neurochemical characterization of a Drosophila dysbindin mutant supports the contribution of serotonin to schizophrenia negative symptoms

Mutations in the dystrobrevin binding protein 1 (DTNBP1) gene that encodes for the dysbindin-1 protein, are associated with a higher risk for schizophrenia. Interestingly, individuals carrying high-risk alleles in this gene have been associated with an increased incidence of negative symptoms for the disease, which include anhedonia, avolition and social withdrawal. Here we evaluated behavioral and neurochemical changes in a hypomorphic Drosophila mutant for the orthologue of human Dysbindin-1, dysb¹. Mutant dysb¹ flies exhibit altered social space parameters, suggesting asocial behavior, accompanied by reduced olfactory performance. Moreover, dysb¹ mutant flies show poor performance in basal and startle-induced locomotor activity. We also report a reduction in serotonin brain levels and changes in the expression of the Drosophila serotonin transporter (dSERT) in dysb¹ flies. Our data show that the serotonin-releasing amphetamine derivative 4-methylthioamphetamine (4-MTA) modulates social spacing and locomotion in control flies, suggesting that serotonergic circuits modulate these behaviors. 4-MTA was unable to modify the behavioral deficiencies in mutant flies, which is consistent with the idea that the efficiency of pharmacological agents acting at dSERT depends on functional serotonergic circuits. Thus, our data show that the dysb¹ mutant exhibits behavioral deficits that mirror some aspects of the endophenotypes associated with the negative symptoms of schizophrenia. We argue that at least part of the behavioral aspects associated with these symptoms could be explained by a serotonergic deficit. The dysb¹ mutant presents an opportunity to study the molecular underpinnings of schizophrenia negative symptoms and reveals new potential targets for treatment of the disease.

Retinal biomarkers and pharmacological targets for Hermansky-Pudlak syndrome 7

Deletion of dystrobrevin binding protein 1 has been linked to Hermansky-Pudlak syndrome type 7 (HPS-7), a rare disease characterized by oculocutaneous albinism and retinal dysfunction. We studied dysbindin-1 null mutant mice (Dys^−/−) to shed light on retinal neurodevelopment defects in HPS-7. We analyzed the expression of a focused set of miRNAs in retina of wild type (WT), Dys^+/− and Dys^−/− mice. We also investigated the retinal function of these mice through electroretinography (ERG). We found that miR-101-3p, miR-137, miR-186-5p, miR-326, miR-382-5p and miR-876-5p were up-regulated in Dys^−/−mice retina. Dys^−/− mice showed significant increased b-wave in ERG, compared to WT mice. Bioinformatic analysis highlighted that dysregulated miRNAs target synaptic plasticity and dopaminergic signaling pathways, affecting retinal functions of Dys^−/− mice. Overall, the data indicate potential mechanisms in retinal neurodevelopment of Dys^−/− mice, which may have translational significance in HSP-7 patients, both in terms of diagnostic/prognostic biomarkers and novel pharmacological targets.

NCBP2 modulates neurodevelopmental defects of the 3q29 deletion in Drosophila and Xenopus laevis models

The 1.6 Mbp deletion on chromosome 3q29 is associated with a range of neurodevelopmental disorders, including schizophrenia, autism, microcephaly, and intellectual disability. Despite its importance towards neurodevelopment, the role of individual genes, genetic interactions, and disrupted biological mechanisms underlying the deletion have not been thoroughly characterized. Here, we used quantitative methods to assay Drosophila melanogaster and Xenopus laevis models with tissue-specific individual and pairwise knockdown of 14 homologs of genes within the 3q29 region. We identified developmental, cellular, and neuronal phenotypes for multiple homologs of 3q29 genes, potentially due to altered apoptosis and cell cycle mechanisms during development. Using the fly eye, we screened for 314 pairwise knockdowns of homologs of 3q29 genes and identified 44 interactions between pairs of homologs and 34 interactions with other neurodevelopmental genes. Interestingly, NCBP2 homologs in Drosophila (Cbp20) and X. laevis (ncbp2) enhanced the phenotypes of homologs of the other 3q29 genes, leading to significant increases in apoptosis that disrupted cellular organization and brain morphology. These cellular and neuronal defects were rescued with overexpression of the apoptosis inhibitors Diap1 and xiap in both models, suggesting that apoptosis is one of several potential biological mechanisms disrupted by the deletion. NCBP2 was also highly connected to other 3q29 genes in a human brain-specific interaction network, providing support for the relevance of our results towards the human deletion. Overall, our study suggests that NCBP2-mediated genetic interactions within the 3q29 region disrupt apoptosis and cell cycle mechanisms during development.

Rare copy-number variants, or large deletions and duplications in the genome, are associated with a wide range of neurodevelopmental disorders. The 3q29 deletion confers an increased risk for schizophrenia and autism. To understand the conserved biological mechanisms that are disrupted by this deletion, we systematically tested 14 individual homologs and 314 pairwise interactions of 3q29 genes for neuronal, cellular, and developmental phenotypes in Drosophila melanogaster and Xenopus laevis models. We found that multiple homologs of genes within the deletion region contribute towards developmental defects, such as larval lethality and disrupted cellular organization. Interestingly, we found that NCBP2 acts as a key modifier gene within the region, enhancing the developmental phenotypes of each of the homologs for other 3q29 genes and leading to disruptions in apoptosis and cell cycle pathways. Our results suggest that multiple genes within the 3q29 region interact with each other through shared mechanisms and jointly contribute to neurodevelopmental defects.

Developmental Genes and Regulatory Proteins, Domains of Cognitive Impairment in Schizophrenia Spectrum Psychosis and Implications for Antipsychotic Drug Discovery: The Example of Dysbindin-1 Isoforms and Beyond

Alongside positive and negative symptomatology, deficits in working memory, attention, selective learning processes, and executive function have been widely documented in schizophrenia spectrum psychosis. These cognitive abnormalities are strongly associated with impairment across multiple function domains and are generally treatment-resistant. The DTNBP1 (dystrobrevin-binding protein-1) gene, encoding dysbindin, is considered a risk factor for schizophrenia and is associated with variation in cognitive function in both clinical and nonclinical samples. Downregulation of DTNBP1 expression in dorsolateral prefrontal cortex and hippocampal formation of patients with schizophrenia has been suggested to serve as a primary pathophysiological process. Described as a "hub," dysbindin is an important regulatory protein that is linked with multiple complexes in the brain and is involved in a wide variety of functions implicated in neurodevelopment and neuroplasticity. The expression pattern of the various dysbindin isoforms (-1A, -1B, -1C) changes depending upon stage of brain development, tissue areas and subcellular localizations, and can involve interaction with different protein partners. We review evidence describing how sequence variation in DTNBP1 isoforms has been differentially associated with schizophrenia-associated symptoms. We discuss results linking these isoform proteins, and their interacting molecular partners, with cognitive dysfunction in schizophrenia, including evidence from drosophila through to genetic mouse models of dysbindin function. Finally, we discuss preclinical evidence investigating the antipsychotic potential of molecules that influence dysbindin expression and functionality. These studies, and other recent work that has extended this approach to other developmental regulators, may facilitate identification of novel molecular pathways leading to improved antipsychotic treatments.

Sleep/Wake Disruption in a Mouse Model of BLOC-1 Deficiency

Mice lacking a functional Biogenesis of Lysosome-related Organelles Complex 1 (BLOC-1), such as those of the pallid line, display cognitive and behavioural impairments reminiscent of those presented by individuals with intellectual and developmental disabilities. Although disturbances in the sleep/wake cycle are commonly lamented by these individuals, the underlying mechanisms, including the possible role of the circadian timing system, are still unknown. In this paper, we have explored sleep/circadian malfunctions and underlying mechanisms in BLOC-1-deficient pallid mice. These mutants exhibited less sleep behaviour in the beginning of the resting phase than wild-type mice with a more broken sleeping pattern in normal light-dark conditions. Furthermore, the strength of the activity rhythms in the mutants were reduced with significantly more fragmentation and lower precision than in age-matched controls. These symptoms were accompanied by an abnormal preference for the open arm in the elevated plus maze in the day and poor performance in the novel object recognition at night. At the level of the central circadian clock (the suprachiasmatic nucleus, SCN), loss of BLOC-1 caused subtle morphological changes including a larger SCN and increased expression of the relative levels of the clock gene Per2 product during the day but did not affect the neuronal activity rhythms. In the hippocampus, the pallid mice presented with anomalies in the cytoarchitecture of the Dentate Gyrus granule cells, but not in CA1 pyramidal neurones, along with altered PER2 protein levels as well as reduced pCREB/tCREB ratio during the day. Our findings suggest that lack of BLOC-1 in mice disrupts the sleep/wake cycle and performance in behavioural tests associated with specific alterations in cytoarchitecture and protein expression.

Big Lessons from Tiny Flies: Drosophila melanogaster as a Model to Explore Dysfunction of Dopaminergic and Serotonergic Neurotransmitter Systems

The brain of Drosophila melanogaster is comprised of some 100,000 neurons, 127 and 80 of which are dopaminergic and serotonergic, respectively. Their activity regulates behavioral functions equivalent to those in mammals, e.g., motor activity, reward and aversion, memory formation, feeding, sexual appetite, etc. Mammalian dopaminergic and serotonergic neurons are known to be heterogeneous. They differ in their projections and in their gene expression profile. A sophisticated genetic tool box is available, which allows for targeting virtually any gene with amazing precision in Drosophila melanogaster. Similarly, Drosophila genes can be replaced by their human orthologs including disease-associated alleles. Finally, genetic manipulation can be restricted to single fly neurons. This has allowed for addressing the role of individual neurons in circuits, which determine attraction and aversion, sleep and arousal, odor preference, etc. Flies harboring mutated human orthologs provide models which can be interrogated to understand the effect of the mutant protein on cell fate and neuronal connectivity. These models are also useful for proof-of-concept studies to examine the corrective action of therapeutic strategies. Finally, experiments in Drosophila can be readily scaled up to an extent, which allows for drug screening with reasonably high throughput.

Disrupted-in-Schizophrenia-1 (DISC1) protein disturbs neural function in multiple disease-risk pathways

Although the genetic contribution is under debate, biological studies in multiple mouse models have suggested that the Disrupted-in-Schizophrenia-1 (DISC1) protein may contribute to susceptibility to psychiatric disorders. In the present study, we took the advantages of the Drosophila model to dissect the molecular pathways that can be affected by DISC1 in the context of pathology-related phenotypes. We found that three pathways that include the homologs of Drosophila Dys, Trio, and Shot were downregulated by introducing a C-terminal truncated mutant DISC1. Consistently, these three molecules were downregulated in the induced pluripotent stem cell-derived forebrain neurons from the subjects carrying a frameshift deletion in DISC1 C-terminus. Importantly, the three pathways were underscored in the pathophysiology of psychiatric disorders in bioinformatics analysis. Taken together, our findings are in line with the polygenic theory of psychiatric disorders.

Neurodevelopmental disease mechanisms, primary cilia, and endosomes converge on the BLOC-1 and BORC complexes

The biogenesis of lysosome-related organelles complex-1 (BLOC-1) and the bloc-one-related complex (BORC) are the cytosolic protein complexes required for specialized membrane protein traffic along the endocytic route and the spatial distribution of endosome-derived compartments, respectively. BLOC-1 and BORC complex subunits and components of their interactomes have been associated with the risk and/or pathomechanisms of neurodevelopmental disorders. Thus, cellular processes requiring BLOC-1 and BORC interactomes have the potential to offer novel insight into mechanisms underlying behavioral defects. We focus on interactions between BLOC-1 or BORC subunits with the actin and microtubule cytoskeleton, membrane tethers, and SNAREs. These interactions highlight requirements for BLOC-1 and BORC in membrane movement by motors, control of actin polymerization, and targeting of membrane proteins to specialized cellular domains such as the nerve terminal and the primary cilium. We propose that the endosome-primary cilia pathway is an underappreciated hub in the genesis and mechanisms of neurodevelopmental disorders. © 2017 Wiley Periodicals, Inc. Develop Neurobiol 78: 311-330, 2018.

The Proteome of BLOC-1 Genetic Defects Identifies the Arp2/3 Actin Polymerization Complex to Function Downstream of the Schizophrenia Susceptibility Factor Dysbindin at the Synapse

Proteome modifications downstream of monogenic or polygenic disorders have the potential to uncover novel molecular mechanisms participating in pathogenesis and/or extragenic modification of phenotypic expression. We tested this idea by determining the proteome sensitive to genetic defects in a locus encoding dysbindin, a protein required for synapse biology and implicated in schizophrenia risk. We applied quantitative mass spectrometry to identify proteins expressed in neuronal cells the abundance of which was altered after downregulation of the schizophrenia susceptibility factor dysbindin (Bloc1s8) or two other dysbindin-interacting polypeptides, which assemble into the octameric biogenesis of lysosome-related organelles complex 1 (BLOC-1). We found 491 proteins sensitive to dysbindin and BLOC-1 loss of function. Gene ontology of these 491 proteins singled out the actin cytoskeleton and the actin polymerization factor, the Arp2/3 complex, as top statistical molecular pathways contained within the BLOC-1-sensitive proteome. Subunits of the Arp2/3 complex were downregulated by BLOC-1 loss of function, thus affecting actin dynamics in early endosomes of BLOC-1-deficient cells. Furthermore, we demonstrated that Arp2/3, dysbindin, and subunits of the BLOC-1 complex biochemically and genetically interact, modulating Drosophila melanogaster synapse morphology and homeostatic synaptic plasticity. Our results indicate that ontologically prioritized proteomics identifies novel pathways that modify synaptic phenotypes associated with neurodevelopmental disorder gene defects.

SIGNIFICANCE STATEMENT

The mechanisms associated with schizophrenia are mostly unknown despite the increasing number of genetic loci identified that increase disease risk. We present an experimental strategy that impartially and comprehensively interrogates the proteome of neurons to identify effects of genetic mutations in a schizophrenia risk factor, dysbindin. We find that the expression of the actin polymerization complex Arp2/3 is reduced in dysbindin-deficient cells, thus affecting actin-dependent phenotypes in two cellular compartments where dysbindin resides, endosomes and presynapses. Our studies indicate that a central cellular structure affected by schizophrenia susceptibility loci is the actin cytoskeleton, an organelle necessary for synaptic function in the presynaptic and postsynaptic compartment.

Dysbindin Deficiency Modifies the Expression of GABA Neuron and Ion Permeation Transcripts in the Developing Hippocampus

The neurodevelopmental factor dysbindin is required for synapse function and GABA interneuron development. Dysbindin protein levels are reduced in the hippocampus of schizophrenia patients. Mouse dysbindin genetic defects and other mouse models of neurodevelopmental disorders share defective GABAergic neurotransmission and, in several instances, a loss of parvalbumin-positive interneuron phenotypes. This suggests that mechanisms downstream of dysbindin deficiency, such as those affecting GABA interneurons, could inform pathways contributing to or ameliorating diverse neurodevelopmental disorders. Here we define the transcriptome of developing wild type and dysbindin null Bloc1s8^sdy/sdy mouse hippocampus in order to identify mechanisms downstream dysbindin defects. The dysbindin mutant transcriptome revealed previously reported GABA parvalbumin interneuron defects. However, the Bloc1s8^sdy/sdy transcriptome additionally uncovered changes in the expression of molecules controlling cellular excitability such as the cation-chloride cotransporters NKCC1, KCC2, and NCKX2 as well as the potassium channel subunits Kcne2 and Kcnj13. Our results suggest that dysbindin deficiency phenotypes, such as GABAergic defects, are modulated by the expression of molecules controlling the magnitude and cadence of neuronal excitability.

The BLOC-1 Subunit Pallidin Facilitates Activity-Dependent Synaptic Vesicle Recycling

Membrane trafficking pathways must be exquisitely coordinated at synaptic terminals to maintain functionality, particularly during conditions of high activity. We have generated null mutations in the Drosophila homolog of pallidin, a central subunit of the biogenesis of lysosome-related organelles complex-1 (BLOC-1), to determine its role in synaptic development and physiology. We find that Pallidin localizes to presynaptic microtubules and cytoskeletal structures, and that the stability of Pallidin protein is highly dependent on the BLOC-1 components Dysbindin and Blos1. We demonstrate that the rapidly recycling vesicle pool is not sustained during high synaptic activity in pallidin mutants, leading to accelerated rundown and slowed recovery. Following intense activity, we observe a loss of early endosomes and a concomitant increase in tubular endosomal structures in synapses without Pallidin. Together, our data reveal that Pallidin subserves a key role in promoting efficient synaptic vesicle recycling and re-formation through early endosomes during sustained activity.

Neuroligins Nlg2 and Nlg4 Affect Social Behavior in Drosophila melanogaster

The genome of Drosophila melanogaster includes homologs to approximately one-third of the currently known human disease genes. Flies and humans share many biological processes, including the principles of information processing by excitable neurons, synaptic transmission, and the chemical signals involved in intercellular communication. Studies on the molecular and behavioral impact of genetic risk factors of human neuro-developmental disorders [autism spectrum disorders (ASDs), schizophrenia, attention deficit hyperactivity disorders, and Tourette syndrome] increasingly use the well-studied social behavior of D. melanogaster, an organism that is amenable to a large variety of genetic manipulations. Neuroligins (Nlgs) are a family of phylogenetically conserved postsynaptic adhesion molecules present (among others) in nematodes, insects, and mammals. Impaired function of Nlgs (particularly of Nlg 3 and 4) has been associated with ASDs in humans and impaired social and communication behavior in mice. Making use of a set of behavioral and social assays, we, here, analyzed the impact of two Drosophila Nlgs, Dnlg2 and Dnlg4, which are differentially expressed at excitatory and inhibitory central nervous synapses, respectively. Both Nlgs seem to be associated with diurnal activity and social behavior. Even though deficiencies in Dnlg2 and Dnlg4 appeared to have no effects on sensory or motor systems, they differentially impacted on social interactions, suggesting that social behavior is distinctly regulated by these Nlgs.

DISC1 causes associative memory and neurodevelopmental defects in fruit flies

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

Unraveling the Neurobiology of Sleep and Sleep Disorders Using Drosophila

Sleep disorders in humans are increasingly appreciated to be not only widespread but also detrimental to multiple facets of physical and mental health. Recent work has begun to shed light on the mechanistic basis of sleep disorders like insomnia, restless legs syndrome, narcolepsy, and a host of others, but a more detailed genetic and molecular understanding of how sleep goes awry is lacking. Over the past 15 years, studies in Drosophila have yielded new insights into basic questions regarding sleep function and regulation. More recently, powerful genetic approaches in the fly have been applied toward studying primary human sleep disorders and other disease states associated with dysregulated sleep. In this review, we discuss the contribution of Drosophila to the landscape of sleep biology, examining not only fundamental advances in sleep neurobiology but also how flies have begun to inform pathological sleep states in humans.

Dysbindin-1 modifies signaling and cellular localization of recombinant, human D₃ and D₂ receptors

Dystrobrevin binding protein-1 (dysbindin-1), a candidate gene for schizophrenia, modulates cognition, synaptic plasticity and frontocortical circuitry and interacts with glutamatergic and dopaminergic transmission. Loss of dysbindin-1 modifies cellular trafficking of dopamine (DA) D2 receptors to increase cell surface expression, but its influence upon signaling has never been characterized. Further, the effects of dysbindin-1 upon closely related D3 receptors remain unexplored. Hence, we examined the impact of dysbindin-1 (isoform A) co-expression on the localization and coupling of human D2L and D3 receptors stably expressed in Chinese hamster ovary or SH-SY5Y cells lacking endogenous dysbindin-1. Dysbindin-1 co-transfection decreased cell surface expression of both D3 and D2L receptors. Further, while their affinity for DA was unchanged, dysbindin-1 reduced the magnitude and potency of DA-induced adenylate cylase recruitment/cAMP production. Dysbindin-1 also blunted the amplitude of DA-induced phosphorylation of ERK1/2 and Akt at both D2L and D3 receptors without, in contrast to cAMP, affecting the potency of DA. Interference with calveolin/clathrin-mediated processes of internalization prevented the modification by dysbindin-1 of ERK1/2 and adenylyl cyclase stimulation at D2L and D3 receptors. Finally, underpinning the specificity of the influence of dysbindin-1 on D2L and D3 receptors, dysbindin-1 did not modify recruitment of adenylyl cyclase by D1 receptors. These observations demonstrate that dysbindin-1 influences cell surface expression of D3 in addition to D2L receptors, and that it modulates activation of their signaling pathways. Accordingly, both a deficiency and an excess of dysbindin-1 may be disruptive for dopaminergic transmission, supporting its link to schizophrenia and other CNS disorders. Dysbindin-1, a candidate gene for schizophrenia, alters D2 receptors cell surface expression. We demonstrate that dysbindin-1 expression also influences cell surface levels of D3 receptors. Further, Dysbindin-1 reduces DA-induced adenylate cylase recruitment/cAMP production and modifies major signaling pathways (Akt and extracellular signal-regulated kinases1/2 (ERK1/2)) of both D2 and D3 receptors. Dysbindin-1 modulates thus D2 and D3 receptor signaling, supporting a link to schizophrenia.

Integrative Proteomics and Metabolomics Analysis of Insect Larva Brain: Novel Insights into the Molecular Mechanism of Insect Wandering Behavior

Before metamorphosis, most holometabolous insects, such as the silkworm studied here, undergo a special phase called the wandering stage. Insects in this stage often display enhanced locomotor activity (ELA). ELA is vital because it ensures that the insect finds a safe and suitable place to live through the pupal stage. The physiological mechanisms of wandering behavior are still unclear. Here, we integrated proteomics and metabolomics approaches to analyze the brain of the lepidopteran insect, silkworm, at the feeding and wandering stages. Using LC-MS/MS and GC-MS, in all we identified 3004 proteins and 37 metabolites at these two stages. Among them, 465 proteins and 22 metabolites were changed. Neural signal transduction proteins and metabolites, such as neurofilament, dopaminergic synapse related proteins, and glutamic acid, were significantly altered, which suggested that active neural conduction occurred in the brain at the wandering stage. We also found decreased dopamine degradation at the wandering stage. The proposed changes in active neural conduction and increased dopamine concentration might induce ELA. In addition, proteins involved in the ubiquitin proteasome system and lysosome pathway were upregulated, revealing that the brain experiences morphological remodeling during metamorphosis. These findings yielded novel insights into the molecular mechanism underlying insect wandering behavior.

Increased dysbindin-1B isoform expression in schizophrenia and its propensity in aggresome formation

Genetic variations in the human dysbindin-1 gene (DTNBP1) have been associated with schizophrenia. As a result of alternative splicing, the human DTNBP1 gene generates at least three distinct protein isoforms, dysbindin-1A, -1B and -1C. Significant effort has focused on dysbindin-1A, an important player in multiple steps of neurodevelopment. However, the other isoforms, dysbindin-1B and dysbindin-1C have not been well characterized. Nor have been associated with human diseases. Here we report an increase in expression of DTNBP1b mRNA in patients with paranoid schizophrenia as compared with healthy controls. A single-nucleotide polymorphism located in intron 9, rs117610176, has been identified and associated with paranoid schizophrenia, and its C allele leads to an increase of DTNBP1b mRNA splicing. Our data show that different dysbindin splicing isoforms exhibit distinct subcellular distribution, suggesting their distinct functional activities. Dysbindin-1B forms aggresomes at the perinuclear region, whereas dysbindin-1A and -1C proteins exhibit diffused patterns in the cytoplasm. Dysbindin-1A interacts with dysbindin-1B, getting recruited to the aggresome structure when co-expressed with dysbindin-1B. Moreover, cortical neurons over-expressing dysbindin-1B show reduction in neurite outgrowth, suggesting that dysbindin-1B may interfere with dysbindin-1A function in a dominant-negative manner. Taken together, our study uncovers a previously unknown association of DTNBP1b expression with schizophrenia in addition to its distinct biochemical and functional properties.

The N-ethylmaleimide-sensitive factor and dysbindin interact to modulate synaptic plasticity

Dysbindin is a schizophrenia susceptibility factor and subunit of the biogenesis of lysosome-related organelles complex 1 (BLOC-1) required for lysosome-related organelle biogenesis, and in neurons, synaptic vesicle assembly, neurotransmission, and plasticity. Protein networks, or interactomes, downstream of dysbindin/BLOC-1 remain partially explored despite their potential to illuminate neurodevelopmental disorder mechanisms. Here, we conducted a proteome-wide search for polypeptides whose cellular content is sensitive to dysbindin/BLOC-1 loss of function. We identified components of the vesicle fusion machinery as factors downregulated in dysbindin/BLOC-1 deficiency in neuroectodermal cells and iPSC-derived human neurons, among them the N-ethylmaleimide-sensitive factor (NSF). Human dysbindin/BLOC-1 coprecipitates with NSF and vice versa, and both proteins colocalized in a Drosophila model synapse. To test the hypothesis that NSF and dysbindin/BLOC-1 participate in a pathway-regulating synaptic function, we examined the role for NSF in dysbindin/BLOC-1-dependent synaptic homeostatic plasticity in Drosophila. As previously described, we found that mutations in dysbindin precluded homeostatic synaptic plasticity elicited by acute blockage of postsynaptic receptors. This dysbindin mutant phenotype is fully rescued by presynaptic expression of either dysbindin or Drosophila NSF. However, neither reduction of NSF alone or in combination with dysbindin haploinsufficiency impaired homeostatic synaptic plasticity. Our results demonstrate that dysbindin/BLOC-1 expression defects result in altered cellular content of proteins of the vesicle fusion apparatus and therefore influence synaptic plasticity.

Neuronal copper homeostasis susceptibility by genetic defects in dysbindin, a schizophrenia susceptibility factor

Environmental factors and susceptible genomes interact to determine the risk of neurodevelopmental disorders. Although few genes and environmental factors have been linked, the intervening cellular and molecular mechanisms connecting a disorder susceptibility gene with environmental factors remain mostly unexplored. Here we focus on the schizophrenia susceptibility gene DTNBP1 and its product dysbindin, a subunit of the BLOC-1 complex, and describe a neuronal pathway modulating copper metabolism via ATP7A. Mutations in ATP7A result in Menkes disease, a disorder of copper metabolism. Dysbindin/BLOC-1 and ATP7A genetically and biochemically interact. Furthermore, disruption of this pathway causes alteration in the transcriptional profile of copper-regulatory and dependent factors in the hippocampus of dysbindin/BLOC-1-null mice. Dysbindin/BLOC-1 loss-of-function alleles do not affect cell and tissue copper content, yet they alter the susceptibility to toxic copper challenges in both mammalian cells and Drosophila. Our results demonstrate that perturbations downstream of the schizophrenia susceptibility gene DTNBP1 confer susceptibility to copper, a metal that in excess is a neurotoxin and whose depletion constitutes a micronutrient deficiency.

Dysbindin gene variability is associated with cognitive abnormalities in first-episode non-affective psychosis

INTRODUCTION

Dystrobrevin-binding protein 1 gene (dysbindin or DTNBP1) has been associated with schizophrenia and cognitive performance. Its expression in areas implicated in cognition such as the dorsolateral prefrontal cortex, as well as its role in dopaminergic and glutamatergic system, has been replicated by several studies. The main aim of this study was to examine the association between DTNBP1 variability and cognitive performance in a sample of 238 patients with a first episode of a non-affective psychosis.

METHODS

Patients, and a comparison sample of 47 healthy subjects, completed an extensive neuropsychological battery. Five single nucleotide polymorphisms (SNPs) within DTNBP1 (rs2619528, rs2619538, rs3213207, rs2619539 and rs760761) and three haplotypes (GACAC, GAGAC and GTGAC) were analysed.

RESULTS

In the group of patients, we found a significant association between two of the DTNBP1 SNPs and one of the haplotypes (rs2619539, rs3213207 and GACAC) and a measure of premorbid IQ [Wechsler Adult Intelligence Scale-3rd Edition (WAIS-III) Vocabulary subtest]. Moreover, one of these SNPs, rs2619539, was also associated with our measure of working memory (WAIS-III Backward digits subtest) and two haplotypes, GAGAC and GTGAC, with our measure of verbal memory (Rey Auditory Verbal Learning Test), of visual memory (Rey Complex Figure Test) in the case of GAGAC, and of speed of processing (WAIS-III Digit Symbol-coding) in the case of GTGAC.

CONCLUSIONS

Our findings add further evidence suggesting an association between dysbindin gene variability and cognitive abnormalities in schizophrenia, providing preliminary evidence of this association since the time of illness onset among minimally medicated patients.

Dopamine dynamics and signaling in Drosophila: an overview of genes, drugs and behavioral paradigms

Changes in dopamine (DA) signaling have been implicated in a number of human neurologic and psychiatric disorders. Similarly, defects in DA signaling in the fruit fly, Drosophila melanogaster, have also been associated with several behavioral defects. As most genes involved in DA synthesis, transport, secretion, and signaling are conserved between species, Drosophila is a powerful genetic model organism to study the regulation of DA signaling in vivo. In this review, we will provide an overview of the genes and drugs that regulate DA biology in Drosophila. Furthermore, we will discuss the behavioral paradigms that are regulated by DA signaling in flies. By analyzing the genes and neuronal circuits that govern such behaviors using sophisticated genetic, pharmacologic, electrophysiologic, and imaging approaches in Drosophila, we will likely gain a better understanding about how this neuromodulator regulates motor tasks and cognition in humans.

Functional characterization of dopamine transporter in vivo using Drosophila melanogaster behavioral assays

Dopamine mediates diverse functions such as motivation, reward, attention, learning/memory and sleep/arousal. Recent studies using model organisms including the fruit fly, have elucidated various physiological functions of dopamine, and identified specific neural circuits for these functions. Flies with mutations in the Drosophila dopamine transporter (dDAT) gene show enhanced dopamine signaling, and short sleep and memory impairment phenotypes. However, understanding the mechanism by which dopamine signaling causes these phenotypes requires an understanding of the dynamics of dopamine release. Here we report the effects of dDAT expression on behavioral traits. We show that dDAT expression in a subset of dopaminergic neurons is sufficient for normal sleep. dDAT expression in other cell types such as Kenyon cells and glial cells can also rescue the short sleep phenotype of dDAT mutants. dDAT mutants also show a down-regulation of the D1-like dopamine receptor dDA1, and this phenotype is rescued when dDAT is expressed in the same cell types in which it rescues sleep. On the other hand, dDAT overexpression in mushroom bodies, which are the target of memory forming dopamine neurons, abolishes olfactory aversive memory. Our data demonstrate that expression of extrasynaptic dopamine transporters can rescue some aspects of dopamine signaling in dopamine transporter mutants. These results provide novel insights into regulatory systems that modulate dopamine signaling.

Mutations in the BLOC-1 subunits dysbindin and muted generate divergent and dosage-dependent phenotypes

Post-mortem analysis has revealed reduced levels of the protein dysbindin in the brains of those suffering from the neurodevelopmental disorder schizophrenia. Consequently, mechanisms controlling the cellular levels of dysbindin and its interacting partners may participate in neurodevelopmental processes impaired in that disorder. To address this question, we studied loss of function mutations in the genes encoding dysbindin and its interacting BLOC-1 subunits. We focused on BLOC-1 mutants affecting synapse composition and function in addition to their established systemic pigmentation, hematological, and lung phenotypes. We tested phenotypic homogeneity and gene dosage effects in the mouse null alleles muted (Bloc1s5(mu/mu)) and dysbindin (Bloc1s8(sdy/sdy)). Transcripts of NMDA receptor subunits and GABAergic interneuron markers, as well as expression of BLOC-1 subunit gene products, were affected differently in the brains of Bloc1s5(mu/mu) and Bloc1s8(sdy/sdy) mice. Unlike Bloc1s8(sdy/sdy), elimination of one or two copies of Bloc1s5 generated indistinguishable pallidin transcript phenotypes. We conclude that monogenic mutations abrogating the expression of a protein complex subunit differentially affect the expression of other complex transcripts and polypeptides as well as their downstream effectors. We propose that the genetic disruption of different subunits of protein complexes and combinations thereof diversifies phenotypic presentation of pathway deficiencies, contributing to the wide phenotypic spectrum and complexity of neurodevelopmental disorders.

Drosophila models of early onset cognitive disorders and their clinical applications

The number of genes known to cause human monogenic diseases is increasing rapidly. For the extremely large, genetically and phenotypically heterogeneous group of intellectual disability (ID) disorders, more than 600 causative genes have been identified to date. However, knowledge about the molecular mechanisms and networks disrupted by these genetic aberrations is lagging behind. The fruit fly Drosophila has emerged as a powerful model organism to close this knowledge gap. This review summarizes recent achievements that have been made in this model and envisions its future contribution to our understanding of ID genetics and neuropathology. The available resources and efficiency of Drosophila place it in a position to tackle the main challenges in the field: mapping functional modules of ID genes to provide conceptually novel insights into the genetic control of cognition, tailored functional studies to improve 'next-generation' diagnostics, and identification of reversible ID phenotypes and medication. Drosophila's behavioral repertoire and powerful genetics also open up perspectives for modeling genetically complex forms of ID and neuropsychiatric disorders, which overlap in their genetic etiologies. In conclusion, Drosophila provides many opportunities to advance future medical genomics of early onset cognitive disorders.

Developmental expression of dysbindin in Muller cells of rat retina

Dysbindin, the product of the DTNBP1 gene, was identified by yeast two hybrid assay as a binding partner of dystrobrevin, a cytosolic component of the dystrophin protein complex. Although its functional role has not yet been completely elucidated, the finding that dysbindin assembles into the biogenesis of lysosome related organelles complex 1 (BLOC-1) suggests that it participates in intracellular trafficking and biogenesis of organelles and vesicles. Dysbindin is ubiquitous and in brain is expressed primarily in neurons. Variations at the dysbindin gene have been associated with increased risk for schizophrenia. As anomalies in retinal function have been reported in patients suffering from neuropsychiatric disorders, we investigated the expression of dysbindin in the retina. Our results show that differentially regulated dysbindin isoforms are expressed in rat retina during postnatal maturation. Interestingly, we found that dysbindin is mainly localized in Müller cells. The identification of dysbindin in glial cells may open new perspectives for a better understanding of the functional involvement of this protein in visual alterations associated to neuropsychiatric disorders.

Replication of association between schizophrenia and chromosome 6p21-6p22.1 polymorphisms in Chinese Han population

Chromosome 6p21-p22.1, spanning the extended major histocompatibility complex (MHC) region, is a highly polymorphic, gene-dense region. It has been identified as a susceptibility locus of schizophrenia in Europeans, Japanese, and Chinese. In our previous two-stage genome-wide association study (GWAS), polymorphisms of zinc finger with KRAB and SCAN domains 4 (ZKSCAN4), nuclear factor-κB-activating protein-like (NKAPL), and piggyBac transposable element derived 1 (PGBD1), localized to chromosome 6p21-p22.1, were strongly associated with schizophrenia. To further investigate the association between polymorphisms at this locus and schizophrenia in the Chinese Han population, we selected eight other single-nucleotide polymorphisms (SNPs) distributed in or near these genes for a case-control association study in an independent sample of 902 cases and 1,091 healthy controls in an attempt to replicate the GWAS results. Four of these eight SNPs (rs12214383, rs1150724, rs3800324, and rs1997660) displayed a nominal difference in allele frequencies between the case and control groups. The association between two of these SNPs and schizophrenia were significant even after Bonferroni correction (rs12000: allele A>G, P = 2.50E-04, odds ratio [OR] = 1.27, 95% confidence interval [CI] = 1.12-1.45; rs1150722: allele C>T, P = 4.28E-05, OR = 0.55, 95% CI = 0.41-0.73). Haplotype ATTGACGC, comprising these eight SNPs (rs2235359, rs2185955, rs12214383, rs12000, rs1150724, rs1150722, rs3800324, and rs1997660), was significantly associated with schizophrenia (P = 6.60E-05). We also performed a combined study of this replication sample and the first-stage GWAS sample. The combined study revealed that rs12000 and rs1150722 were still strongly associated with schizophrenia (rs12000: allele G>A, P(combined) = 0.0019, OR = 0.81; rs1150722: allele G>A, P(combined) = 3.00E-04, OR = 0.61). These results support our findings that locus 6p21-p22.1 is significantly associated with schizophrenia in the Chinese Han population and encourage further studies of the functions of these genetic factors.

Reduced expression of the dysbindin-like gene in the Bombyx mori ov mutant exhibiting mottled translucency of the larval skin

The ov (mottled translucent of Var) mutant, an oily mutant of Bombyx mori, exhibits mottled translucent skin with a varying degree of transparency among individuals. By linkage analysis of 2112 backcross individuals using polymorphic DNA markers, we successfully mapped a 179-kb region of chromosome 20 responsible for the ov phenotype. This region contains nine predicted genes. We compared the mRNA expression of these nine genes between the wild type and mutants and found that the expression of one of them, Bmdysb, was strikingly decreased in the epidermis of ov as well as its allelomorph, ovp. Moreover, its expression level was well correlated with the degree of transparency among individuals. Bmdysb was homologous to DTNBP1 encoding human dysbindin, a subunit of the biogenesis of lysosome-related organelles complex-1. Our results suggest that the translucent skin may be due to repression of Bmdysb in the ov mutants and that Bmdysb plays an important role in the formation and accumulation of urate granules in the silkworm epidermis.

Transient activation of dopaminergic neurons during development modulates visual responsiveness, locomotion and brain activity in a dopamine ontogeny model of schizophrenia

It has been observed that certain developmental environmental risk factors for schizophrenia when modeled in rodents alter the trajectory of dopaminergic development, leading to persistent behavioural changes in adults. This has recently been articulated as the "dopamine ontogeny hypothesis of schizophrenia". To test one aspect of this hypothesis, namely that transient dopaminergic effects during development modulate attention-like behavior and arousal in adults, we turned to a small-brain model, Drosophila melanogaster. By applying genetic tools allowing transient activation or silencing of dopaminergic neurons in the fly brain, we investigated whether a critical window exists during development when altered dopamine (DA) activity levels could lead to impairments in arousal states in adult animals. We found that increased activity in dopaminergic neurons in later stages of development significantly increased visual responsiveness and locomotion, especially in adult males. This misallocation of visual salience and hyperactivity mimicked the effect of acute methamphetamine feeding to adult flies, suggesting up-regulated DA signaling could result from developmental manipulations. Finally, brain recordings revealed significantly reduced gamma-band activity in adult animals exposed to the transient developmental insult. Together, these data support the idea that transient alterations in DA signaling during development can permanently alter behavior in adults, and that a reductionist model such as Drosophila can be used to investigate potential mechanisms underlying complex cognitive disorders such as schizophrenia.