A 200-kb region of human chromosome 22q11.2 confers antipsychotic-responsive behavioral abnormalities in mice

Structural alterations in the amygdala and impaired social incentive learning in a mouse model of a genetic variant associated with neurodevelopmental disorders

Copy number variants (CNVs) are robustly associated with psychiatric disorders and their dimensions and changes in brain structures and behavior. However, as CNVs contain many genes, the precise gene-phenotype relationship remains unclear. Although various volumetric alterations in the brains of 22q11.2 CNV carriers have been identified in humans and mouse models, it is unknown how the genes in the 22q11.2 region individually contribute to structural alterations and associated mental illnesses and their dimensions. Our previous studies have identified Tbx1, a T-box family transcription factor encoded in 22q11.2 CNV, as a driver gene for social interaction and communication, spatial and working memory, and cognitive flexibility. However, it remains unclear how TBX1 impacts the volumes of various brain regions and their functionally linked behavioral dimensions. In this study, we used volumetric magnetic resonance imaging analysis to comprehensively evaluate brain region volumes in congenic Tbx1 heterozygous mice. Our data show that the volumes of anterior and posterior portions of the amygdaloid complex and its surrounding cortical regions were reduced in Tbx1 heterozygous mice. Moreover, we examined the behavioral consequences of an altered volume of the amygdala. Tbx1 heterozygous mice were impaired for their ability to detect the incentive value of a social partner in a task that depends on the amygdala. Our findings identify the structural basis for a specific social dimension associated with loss-of-function variants of TBX1 and 22q11.2 CNV.

Structural alterations in the amygdala and impaired social incentive learning in a mouse model of a genetic variant associated with neurodevelopmental disorders

Copy number variants (CNVs) are robustly associated with psychiatric disorders and their dimensions and changes in brain structures and behavior. However, as CNVs contain many genes, the precise gene-phenotype relationship remains unclear. Although various volumetric alterations in the brains of 22q11.2 CNV carriers have been identified in humans and mouse models, it is unknown how the genes in the 22q11.2 region individually contribute to structural alterations and associated mental illnesses and their dimensions. Our previous studies have identified Tbx1 , a T-box family transcription factor encoded in 22q11.2 CNV, as a driver gene for social interaction and communication, spatial and working memory, and cognitive flexibility. However, it remains unclear how TBX1 impacts the volumes of various brain regions and their functionally linked behavioral dimensions. In this study, we used volumetric magnetic resonance imaging analysis to comprehensively evaluate brain region volumes in congenic Tbx1 heterozygous mice. Our data show that the volumes of anterior and posterior portions of the amygdaloid complex and its surrounding cortical regions were reduced in Tbx1 heterozygous mice. Moreover, we examined the behavioral consequences of an altered volume of the amygdala. Tbx1 heterozygous mice were impaired for their ability to detect the incentive value of a social partner in a task that depends on the amygdala. Our findings identify the structural basis for a specific social dimension associated with loss-of-function variants of TBX1 and 22q11.2 CNV.

Tbx1, a gene encoded in 22q11.2 copy number variant, is a link between alterations in fimbria myelination and cognitive speed in mice

Copy number variants (CNVs) have provided a reliable entry point to identify the structural correlates of atypical cognitive development. Hemizygous deletion of human chromosome 22q11.2 is associated with impaired cognitive function; however, the mechanisms by which the CNVs contribute to cognitive deficits via diverse structural alterations in the brain remain unclear. This study aimed to determine the cellular basis of the link between alterations in brain structure and cognitive functions in mice with a heterozygous deletion of Tbx1, one of the 22q11.2-encoded genes. Ex vivo whole-brain diffusion-tensor imaging (DTI)-magnetic resonance imaging (MRI) in Tbx1 heterozygous mice indicated that the fimbria was the only region with significant myelin alteration. Electron microscopic and histological analyses showed that Tbx1 heterozygous mice exhibited an apparent absence of large myelinated axons and thicker myelin in medium axons in the fimbria, resulting in an overall decrease in myelin. The fimbria of Tbx1 heterozygous mice showed reduced mRNA levels of Ng2, a gene required to produce oligodendrocyte precursor cells. Moreover, postnatal progenitor cells derived from the subventricular zone, a source of oligodendrocytes in the fimbria, produced fewer oligodendrocytes in vitro. Behavioral analyses of these mice showed selectively slower acquisition of spatial memory and cognitive flexibility with no effects on their accuracy or sensory or motor capacities. Our findings provide a genetic and cellular basis for the compromised cognitive speed in patients with 22q11.2 hemizygous deletion.

Dosage sensitivity intolerance of VIPR2 microduplication is disease causative to manifest schizophrenia-like phenotypes in a novel BAC transgenic mouse model

Recent genome-wide association studies (GWAS) have identified copy number variations (CNVs) at chromosomal locus 7q36.3 that significantly contribute to the risk of schizophrenia, with all of the microduplications occurring within a single gene: vasoactive intestinal peptide receptor 2 (VIPR2). To confirm disease causality and translate such a genetic vulnerability into mechanistic and pathophysiological insights, we have developed a series of conditional VIPR2 bacterial artificial chromosome (BAC) transgenic mouse models of VIPR2 CNV. VIPR2 CNV mouse model recapitulates gene expression and signaling deficits seen in human CNV carriers. VIPR2 microduplication in mice elicits prominent dorsal striatal dopamine dysfunction, cognitive, sensorimotor gating, and social behavioral deficits preceded by an increase of striatal cAMP/PKA signaling and the disrupted early postnatal striatal development. Genetic removal of VIPR2 transgene expression via crossing with Drd1a-Cre BAC transgenic mice rescued the dopamine D2 receptor abnormality and multiple behavioral deficits, implicating a pathogenic role of VIPR2 overexpression in dopaminoceptive neurons. Thus, our results provide further evidence to support the GWAS studies that the dosage sensitivity intolerance of VIPR2 is disease causative to manifest schizophrenia-like dopamine, cognitive, and social behavioral deficits in mice. The conditional BAC transgenesis offers a novel strategy to model CNVs with a gain-of -copies and facilitate the genetic dissection of when/where/how the genetic vulnerabilities affect development, structure, and function of neural circuits. Our findings have important implications for therapeutic development, and the etiology-relevant mouse model provides a useful preclinical platform for drug discovery.

Genotypic and phenotypic variability of 22q11.2 microduplications: An institutional experience

Duplications in the 22q11.2 region can cause 22q11.2 duplication syndrome and encompass a variety of phenotypes including developmental delays, facial abnormalities, cardiovascular defects, central nervous system delays, and other congenital abnormalities. However, the contribution of these contiguous duplicated regions to the clinical phenotypes has not been fully elucidated. In this study, we identified nine patients carrying different 22q11.2 microduplications detected by chromosomal microarray. Of these patients, seven pediatric patients presented with various clinical features including two neonate cases died shortly after birth, and two healthy adults. We examined region specific genotype-phenotype associations and found unpredictability associated with 22q11.2 duplications in these nine patients.

Association of genetic variants at 22q11.2 chromosomal region with cognitive performance in Japanese patients with schizophrenia

22q11.2 heterozygous multigene deletions confer an increased risk of schizophrenia with marked impairment of cognition. We explored whether genes on 22q11.2 are associated with cognitive performance in patients with idiopathic schizophrenia. A total of 240 schizophrenia patients and 240 healthy controls underwent the Japanese-language version of the Brief Assessment of Cognition in Schizophrenia (BACS) and were genotyped for 115 tag single-nucleotide polymorphisms (tag SNPs) at the 22q11.2 region using the golden gate assay (Illumina®). Associations between z-scores of the BACS cognitive domains and SNPs and haplotypes were analyzed using linear regression in PLINK 1.07. An additional set of 149 patients with bipolar disorder were included for cognitive assessment and selected SNPs were genotyped using real-time PCR. Patients with schizophrenia and bipolar disorder showed qualitatively comparable profiles of cognitive impairment across BACS subdomains, as revealed by significant correlation between the two groups in the resulting cognitive effect sizes relative to controls. rs4819522 (TBX1) and rs2238769 (UFD1L) were significantly and nominally associated, respectively, with symbol coding in patients with schizophrenia. Haplotype analyses revealed that haplotypes containing the A allele at rs4819522 and G allele at rs2238769 showed significant negative associations with symbol coding in patients with schizophrenia. There was no effect of any haplotypes on cognition in patients with bipolar disorder. Our results have implications for the understanding of the role of haplotypes of UFD1L and TBX1 genes associated with symbol coding in patients with schizophrenia. Further replication studies in a cohort of newly diagnosed patients and other ethnicities are warranted.

Modeling and Predicting Developmental Trajectories of Neuropsychiatric Dimensions Associated With Copy Number Variations

Copy number variants, such as duplications and hemizygous deletions at chromosomal loci of up to a few million base pairs, are highly associated with psychiatric disorders. Hemizygous deletions at human chromosome 22q11.2 were found to be associated with elevated instances of schizophrenia and autism spectrum disorder in 1992 and 2002, respectively. Following these discoveries, many mouse models have been developed and tested to analyze the effects of gene dose alterations in small chromosomal segments and single genes of 22q11.2. Despite several limitations to modeling mental illness in mice, mouse models have identified several genes on 22q11.2-Tbx1, Dgcr8, Comt, Sept5, and Prodh-that contribute to dimensions of autism spectrum disorder and schizophrenia, including working memory, social communication and interaction, and sensorimotor gating. Mouse studies have identified that heterozygous deletion of Tbx1 results in defective social communication during the neonatal period and social interaction deficits during adolescence/adulthood. Overexpression of Tbx1 or Comt in adult neural progenitor cells in the hippocampus delays the developmental maturation of working memory capacity. Collectively, mouse models of variants of these 4 genes have revealed several potential neuronal mechanisms underlying various aspects of psychiatric disorders, including adult neurogenesis, microRNA processing, catecholamine metabolism, and synaptic transmission. The validity of the mouse data would be ultimately tested when therapies or drugs based on such potential mechanisms are applied to humans.

Episodic Behavioural Regression in an 8-Year-Old Female: Sequelae of 22q11.2 Duplication Syndrome

22q11.2 duplication syndrome is a recently discovered genetic syndrome with unclear neuropsychiatric sequelae. While its connection to 22q11.2 deletion syndrome is actively investigated, case reports on the neuropsychiatric sequelae of affected individuals have been previously described, largely focusing on comorbid autism spectrum disorder. Here, we present the case of an 8-year-old female experiencing episodes of severe behavioural regression following medical illness. We analyze the case and relate it to the available literature and identify potential risk factors.

Critical reappraisal of mechanistic links of copy number variants to dimensional constructs of neuropsychiatric disorders in mouse models

Copy number variants are deletions and duplications of a few thousand to million base pairs and are associated with extraordinarily high levels of autism spectrum disorder, schizophrenia, intellectual disability, or attention-deficit hyperactivity disorder. The unprecedented levels of robust and reproducible penetrance of copy number variants make them one of the most promising and reliable entry points to delve into the mechanistic bases of many mental disorders. However, the precise mechanistic bases of these associations still remain elusive in humans due to the many genes encoded in each copy number variant and the diverse associated phenotypic features. Genetically engineered mice have provided a technical means to ascertain precise genetic mechanisms of association between copy number variants and dimensional aspects of mental illnesses. Molecular, cellular, and neuronal phenotypes can be detected as potential mechanistic substrates for various behavioral constructs of mental illnesses. However, mouse models come with many technical pitfalls. Genetic background is not well controlled in many mouse models, leading to rather obvious interpretative issues. Dose alterations of many copy number variants and single genes within copy number variants result in some molecular, cellular, and neuronal phenotypes without a behavioral phenotype or with a behavioral phenotype opposite to what is seen in humans. In this review, I discuss technical and interpretative pitfalls of mouse models of copy number variants and highlight well-controlled studies to suggest potential neuronal mechanisms of dimensional aspects of mental illnesses. Mouse models of copy number variants represent toeholds to achieve a better understanding of the mechanistic bases of dimensions of neuropsychiatric disorders and thus for development of mechanism-based therapeutic options in humans.

Copy number elevation of 22q11.2 genes arrests the developmental maturation of working memory capacity and adult hippocampal neurogenesis

Working memory capacity, a critical component of executive function, expands developmentally from childhood through adulthood. Anomalies in this developmental process are seen in individuals with autism spectrum disorder (ASD), schizophrenia and intellectual disabilities (ID), implicating this atypical process in the trajectory of developmental neuropsychiatric disorders. However, the cellular and neuronal substrates underlying this process are not understood. Duplication and triplication of copy number variants of 22q11.2 are consistently and robustly associated with cognitive deficits of ASD and ID in humans, and overexpression of small 22q11.2 segments recapitulates dimensional aspects of developmental neuropsychiatric disorders in mice. We capitalized on these two lines of evidence to delve into the cellular substrates for this atypical development of working memory. Using a region- and cell-type-selective gene expression approach, we demonstrated that copy number elevations of catechol-O-methyl-transferase (COMT) or Tbx1, two genes encoded in the two small 22q11.2 segments, in adult neural stem/progenitor cells in the hippocampus prevents the developmental maturation of working memory capacity in mice. Moreover, copy number elevations of COMT or Tbx1 reduced the proliferation of adult neural stem/progenitor cells in a cell-autonomous manner in vitro and migration of their progenies in the hippocampus granular layer in vivo. Our data provide evidence for the novel hypothesis that copy number elevations of these 22q11.2 genes alter the developmental trajectory of working memory capacity via suboptimal adult neurogenesis in the hippocampus.

Screening for Mutations in the TBX1 Gene on Chromosome 22q11.2 in Schizophrenia

A higher-than-expected frequency of schizophrenia in patients with 22q11.2 deletion syndrome suggests that chromosome 22q11.2 harbors the responsive genes related to the pathophysiology of schizophrenia. The TBX1 gene, which maps to the region on chromosome 22q11.2, plays a vital role in neuronal functions. Haploinsufficiency of the TBX1 gene is associated with schizophrenia endophenotype. This study aimed to investigate whether the TBX1 gene is associated with schizophrenia. We searched for mutations in the TBX1 gene in 652 patients with schizophrenia and 567 control subjects using a re-sequencing method and conducted a reporter gene assay. We identified six SNPs and 25 rare mutations with no association with schizophrenia from Taiwan. Notably, we identified two rare schizophrenia-specific mutations (c.-123G>C and c.-11delC) located at 5' UTR of the TBX1 gene. The reporter gene assay showed that c.-123C significantly decreased promoter activity, while c.-11delC increased promoter activity compared with the wild-type. Our findings suggest that the TBX1 gene is unlikely a major susceptible gene for schizophrenia in an ethnic Chinese population for Taiwan, but a few rare mutations in the TBX1 gene may contribute to the pathogenesis of schizophrenia in some patients.

Analysis of induced pluripotent stem cells carrying 22q11.2 deletion

Given the complexity and heterogeneity of the genomic architecture underlying schizophrenia, molecular analyses of these patients with defined and large effect-size genomic defects could provide valuable clues. We established human-induced pluripotent stem cells from two schizophrenia patients with the 22q11.2 deletion (two cell lines from each subject, total of four cell lines) and three controls (total of four cell lines). Neurosphere size, neural differentiation efficiency, neurite outgrowth, cellular migration and the neurogenic-to-gliogenic competence ratio were significantly reduced in patient-derived cells. As an underlying mechanism, we focused on the role of DGCR8, a key gene for microRNA (miRNA) processing and mapped in the deleted region. In mice, Dgcr8 hetero-knockout is known to show a similar phenotype of reduced neurosphere size (Ouchi et al., 2013). The miRNA profiling detected reduced expression levels of miRNAs belonging to miR-17/92 cluster and miR-106a/b in the patient-derived neurospheres. Those miRNAs are reported to target p38α, and conformingly the levels of p38α were upregulated in the patient-derived cells. p38α is known to drive gliogenic differentiation. The inhibition of p38 activity by SB203580 in patient-derived neurospheres partially restored neurogenic competence. Furthermore, we detected elevated expression of GFAP, a gliogenic (astrocyte) marker, in postmortem brains from schizophrenia patients without the 22q11.2 deletion, whereas inflammation markers (IL1B and IL6) remained unchanged. In contrast, a neuronal marker, MAP2 expressions were decreased in schizophrenia brains. These results suggest that a dysregulated balance of neurogenic-to-gliogenic competence may underlie neurodevelopmental disorders such as schizophrenia.

Emerging roles of ARHGAP33 in intracellular trafficking of TrkB and pathophysiology of neuropsychiatric disorders

Intracellular trafficking of receptor proteins is essential for neurons to detect various extracellular factors during the formation and refinement of neural circuits. However, the precise mechanisms underlying the trafficking of neurotrophin receptors to synapses remain elusive. Here, we demonstrate that a brain-enriched sorting nexin, ARHGAP33, is a new type of regulator for the intracellular trafficking of TrkB, a high-affinity receptor for brain-derived neurotrophic factor. ARHGAP33 knockout (KO) mice exhibit reduced expression of synaptic TrkB, impaired spine development and neuropsychiatric disorder-related behavioural abnormalities. These deficits are rescued by specific pharmacological enhancement of TrkB signalling in ARHGAP33 KO mice. Mechanistically, ARHGAP33 interacts with SORT1 to cooperatively regulate TrkB trafficking. Human ARHGAP33 is associated with brain phenotypes and reduced SORT1 expression is found in patients with schizophrenia. We propose that ARHGAP33/SORT1-mediated TrkB trafficking is essential for synapse development and that the dysfunction of this mechanism may be a new molecular pathology of neuropsychiatric disorders.

The molecular mechanisms of neurotrophin receptor trafficking are only partially understood. Here the authors show that ARHGAP33 interacts with SORT1 to regulate TrkB trafficking, the dysfunction of which impairs synapse development and leads to schizophrenia-related behavioural abnormalities in mice.

A mouse model that recapitulates cardinal features of the 15q13.3 microdeletion syndrome including schizophrenia- and epilepsy-related alterations

BACKGROUND

Genome-wide scans have uncovered rare copy number variants conferring high risk of psychiatric disorders. The 15q13.3 microdeletion is associated with a considerably increased risk of idiopathic generalized epilepsy, intellectual disability, and schizophrenia.

METHODS

A 15q13.3 microdeletion mouse model (Df[h15q13]/+) was generated by hemizygous deletion of the orthologous region and characterized with focus on schizophrenia- and epilepsy-relevant parameters.

RESULTS

Df(h15q13)/+ mice showed marked changes in neuronal excitability in acute seizure assays, with increased propensity to develop myoclonic and absence-like seizures but decreased propensity for clonic and tonic seizures. Furthermore, they had impaired long-term spatial reference memory and a decreased theta frequency in hippocampus and prefrontal cortex. Electroencephalogram characterization revealed auditory processing deficits similar to those observed in schizophrenia. Gamma band power was increased during active state, but evoked gamma power following auditory stimulus (40 Hz) was dramatically reduced, mirroring observations in patients with schizophrenia. In addition, Df(h15q13)/+ mice showed schizophrenia-like decreases in amplitudes of auditory evoked potentials. Although displaying a grossly normal behavior, Df(h15q13)/+ mice are more aggressive following exposure to mild stressors, similar to what is described in human deletion carriers. Furthermore, Df(h15q13)/+ mice have increased body weight, and a similar increase in body weight was subsequently found in a sample of human subjects with 15q13.3 deletion.

CONCLUSIONS

The Df(h15q13)/+ mouse shows similarities to several alterations related to the 15q13.3 microdeletion syndrome, epilepsy, and schizophrenia, offering a novel tool for addressing the underlying biology of these diseases.

Copy number variation at 22q11.2: from rare variants to common mechanisms of developmental neuropsychiatric disorders

Recently discovered genome-wide rare copy number variants (CNVs) have unprecedented levels of statistical association with many developmental neuropsychiatric disorders, including schizophrenia, autism spectrum disorders, intellectual disability and attention deficit hyperactivity disorder. However, as CNVs often include multiple genes, causal genes responsible for CNV-associated diagnoses and traits are still poorly understood. Mouse models of CNVs are in use to delve into the precise mechanisms through which CNVs contribute to disorders and associated traits. Based on human and mouse model studies on rare CNVs within human chromosome 22q11.2, we propose that alterations of a distinct set of multiple, noncontiguous genes encoded in this chromosomal region, in concert with modulatory impacts of genetic background and environmental factors, variably shift the probabilities of phenotypes along a predetermined developmental trajectory. This model can be further extended to the study of other CNVs and may serve as a guide to help characterize the impact of genes in developmental neuropsychiatric disorders.

Chronic overload of SEPT4, a parkin substrate that aggregates in Parkinson's disease, causes behavioral alterations but not neurodegeneration in mice

Background

In autosomal recessive early-onset Parkinsonism (PARK2), the pathogenetic process from the loss of function of a ubiquitin ligase parkin to the death of dopamine neurons remains unclear. A dominant hypothesis attributes the neurotoxicity to accumulated substrates that are exempt from parkin-mediated degradation. Parkin substrates include two septins; SEPT4/CDCrel-2 which coaggregates with α-synuclein as Lewy bodies in Parkinson’s disease, and its closest homolog SEPT5/CDCrel-1/PNUTL1 whose overload with viral vector can rapidly eliminate dopamine neurons in rats. However, chronic effects of pan-neural overload of septins have never been examined in mammals. To address this, we established a line of transgenic mice that express the largest gene product SEPT4^54kDa via the prion promoter in the entire brain.

Results

Histological examination and biochemical quantification of SEPT4-associated proteins including α-synuclein and the dopamine transporter in the nigrostriatal dopamine neurons found no significant difference between Sept4^Tg/+ and wild-type littermates. Thus, the hypothetical pathogenicity by the chronic overload of SEPT4 alone, if any, is insufficient to trigger neurodegenerative process in the mouse brain. Intriguingly, however, a systematic battery of behavioral tests revealed unexpected abnormalities in Sept4^Tg/+ mice that include consistent attenuation of voluntary activities in distinct behavioral paradigms and altered social behaviors.

Conclusions

Together, these data indicate that septin dysregulations commonly found in postmortem human brains with Parkinson’s disease, schizophrenia and bipolar disorders may be responsible for a subset of behavioral abnormalities in the patients.

Alterations of social interaction through genetic and environmental manipulation of the 22q11.2 gene Sept5 in the mouse brain

Social behavior dysfunction is a symptomatic element of schizophrenia and autism spectrum disorder (ASD). Although altered activities in numerous brain regions are associated with defective social cognition and perception, the causative relationship between these altered activities and social cognition and perception-and their genetic underpinnings-are not known in humans. To address these issues, we took advantage of the link between hemizygous deletion of human chromosome 22q11.2 and high rates of social behavior dysfunction, schizophrenia and ASD. We genetically manipulated Sept5, a 22q11.2 gene, and evaluated its role in social interaction in mice. Sept5 deficiency, against a high degree of homogeneity in a congenic genetic background, selectively impaired active affiliative social interaction in mice. Conversely, virally guided overexpression of Sept5 in the hippocampus or, to a lesser extent, the amygdala elevated levels of active affiliative social interaction in C57BL/6J mice. Congenic knockout mice and mice overexpressing Sept5 in the hippocampus or amygdala were indistinguishable from control mice in novelty and olfactory responses, anxiety or motor activity. Moreover, post-weaning individual housing, an environmental condition designed to reduce stress in male mice, selectively raised levels of Sept5 protein in the amygdala and increased active affiliative social interaction in C57BL/6J mice. These findings identify this 22q11.2 gene in the hippocampus and amygdala as a determinant of social interaction and suggest that defective social interaction seen in 22q11.2-associated schizophrenia and ASD can be genetically and environmentally modified by altering this 22q11.2 gene.

Mouse Models of 22q11.2-Associated Autism Spectrum Disorder

Copy number variation (CNV) of human chromosome 22q11.2 is associated with an elevated rate of autism spectrum disorder (ASD) and represents one of syndromic ASDs with rare genetic variants. However, the precise genetic basis of this association remains unclear due to its relatively large hemizygous and duplication region, including more than 30 genes. Previous studies using genetic mouse models suggested that although not all 22q11.2 genes contribute to ASD symptomatology, more than one 22q11.2 genes have distinct phenotypic targets for ASD symptoms. Our data show that deficiency of the two 22q11.2 genesTbx1 and Sept5 causes distinct phenotypic sets of ASD symptoms.

Tbx1: identification of a 22q11.2 gene as a risk factor for autism spectrum disorder in a mouse model

Although twin studies indicate clear genetic bases of autism spectrum disorder (ASD), the precise mechanisms through which genetic variations causally result in ASD are poorly understood. Individuals with 3 Mb and nested 1.5 Mb hemizygosity of the chromosome 22q11.2 represent genetically identifiable cases of ASD. However, because more than 30 genes are deleted even in the minimal deletion cases of 22q11.2 deficiency, the individual 22q11.2 gene(s) responsible for ASD remain elusive. Here, we examined the impact of constitutive heterozygosity of Tbx1, a 22q11.2 gene, on the behavioral phenotypes of ASD and characterized the regional and cellular expression of its mRNA and protein in mice. Congenic Tbx1 heterozygous (HT) mice were impaired in social interaction, ultrasonic vocalization, memory-based behavioral alternation, working memory and thigmotaxis, compared with wild-type (WT) mice. These phenotypes were not due to non-specific alterations in olfactory function, exploratory behavior, motor movement or anxiety-related behavior. Tbx1 mRNA and protein were ubiquitously expressed throughout the brains of C57BL/6J mice, but protein expression was enriched in regions that postnatally retain the capacity of neurogenesis, and in fact, postnatally proliferating cells expressed Tbx1. In postnatally derived hippocampal culture cells of C57BL/6J mice, Tbx1 levels were higher during proliferation than during differentiation, and expressed in neural progenitor cells, immature and matured neurons and glial cells. Taken together, our data suggest that Tbx1 is a gene responsible for the phenotypes of 22q11.2 hemizygosity-associated ASD possibly through its role in diverse cell types, including postnatally and prenatally generated neurons.

Molecular mechanisms in 22q11 deletion syndrome

It is now well recognized that as well as having a characteristic facial dysmorphology and a range of congenital abnormalities, individuals with chromosome 22q11 deletion syndrome (22q11DS) have a greatly increased risk of developing psychosis, in particular schizophrenia. The majority of deletions span a large 3Mb region at 22q11. However, the presence of affected individuals carrying smaller deletions have not been sufficient to satisfactorily reduce the critical region for the behavioral phenotype beyond a ~1.5Mb region that contains at least 28 genes. By having a shared genetic variant that greatly increases risk to psychosis, individuals with 22q11DS are a relatively homogeneous population to study psychiatric disease. Despite this, the large volume of research performed over the last 15 years suggest that the mechanism by which haploinsufficiency at 22q11 increases risk to psychiatric illness is likely to be complex and it remains uncertain why individuals carrying identical 22q11 deletions can present with such a wide range of neuropsychiatric phenotypes. This review will therefore consider the ways in which deletions at 22q11 are expected to increase risk to develop psychiatric disease by summarizing the work that has been done to investigate three of the most likely disease causing mechanisms: (a) gene dosage sensitivity; (b) unmasking of recessive alleles or functional polymorphism; and (c) position effect.

Supportive evidence for reduced expression of GNB1L in schizophrenia

BACKGROUND

Chromosome 22q11 deletion syndrome (22q11DS) increases the risk of development of schizophrenia more than 10 times compared with that of the general population, indicating that haploinsufficiency of a subset of the more than 20 genes contained in the 22q11DS region could increase the risk of schizophrenia. In the present study, we screened for genes located in the 22q11DS region that are expressed at lower levels in postmortem prefrontal cortex of patients with schizophrenia than in those of controls.

METHODS

Gene expression was screened by Illumina Human-6 Expression BeadChip arrays and confirmed by real-time reverse transcription-polymerase chain reaction assays and Western blot analysis.

RESULTS

Expression of GNB1L was lower in patients with schizophrenia than in control subjects in both Australian (10 schizophrenia cases and 10 controls) and Japanese (43 schizophrenia cases and 11 controls) brain samples. TBX1 could not be evaluated due to its low expression levels. Expression levels of the other genes were not significantly lower in patients with schizophrenia than in control subjects. Association analysis of tag single-nucleotide polymorphisms in the GNB1L gene region did not confirm excess homozygosity in 1918 Japanese schizophrenia cases and 1909 Japanese controls. Haloperidol treatment for 50 weeks increased Gnb1l gene expression in prefrontal cortex of mice.

CONCLUSIONS

Taken together with the impaired prepulse inhibition observed in heterozygous Gnb1l knockout mice reported by the previous study, the present findings support assertions that GNB1L is one of the genes in the 22q11DS region responsible for increasing the risk of schizophrenia.

Hyperactivity, startle reactivity and cell-proliferation deficits are resistant to chronic lithium treatment in adult Nr2e1(frc/frc) mice

The NR2E1 region on Chromosome 6q21-22 has been repeatedly linked to bipolar disorder (BP) and NR2E1 has been associated with BP, and more specifically bipolar I disorder (BPI). In addition, patient sequencing has shown an enrichment of rare candidate-regulatory variants. Interestingly, mice carrying either spontaneous (Nr2e1(frc) ) or targeted (Tlx(-) ) deletions of Nr2e1 (here collectively known as Nr2e1-null) show similar neurological and behavioral anomalies, including hypoplasia of the cerebrum, reduced neural stem cell proliferation, extreme aggression and deficits in fear conditioning; these are the traits that have been observed in some patients with BP. Thus, NR2E1 is a positional and functional candidate for a role in BP. However, no Nr2e1-null mice have been fully evaluated for behaviors used to model BP in rodents or pharmacological responses to drugs effective in treating BP symptoms. In this study we examine Nr2e1(frc/frc) mice, homozygous for the spontaneous deletion, for abnormalities in activity, learning and information processing, and cell proliferation; these are the phenotypes that are either affected in patients with BP or commonly assessed in rodent models of BP. The effect of lithium, a drug used to treat BP, was also evaluated for its ability to attenuate Nr2e1(frc/frc) behavioral and neural stem cell-proliferation phenotypes. We show for the first time that Nr2e1-null mice exhibit extreme hyperactivity in the open field as early as postnatal day 18 and in the home cage, deficits in open-field habituation and passive avoidance, and surprisingly, an absence of acoustic startle. We observed a reduction in neural stem/progenitor cell proliferation in Nr2e1(frc/frc) mice, similar to that seen in other Nr2e1-null strains. These behavioral and cell-proliferation phenotypes were resistant to chronic-adult-lithium treatment. Thus, Nr2e1(frc/frc) mice exhibit behavioral traits used to model BP in rodents, but our results do not support Nr2e1(frc/frc) mice as pharmacological models for BP.

Genome-wide approaches to schizophrenia

Schizophrenia (SZ) is a common and severe psychiatric disorder with both environmental and genetic risk factors, and a high heritability. After over 20 years of molecular genetics research, new molecular strategies, primarily genome-wide association studies (GWAS), have generated major tangible progress. This new data provides evidence for: (1) a number of chromosomal regions with common polymorphisms showing genome-wide association with SZ (the major histocompatibility complex, MHC, region at 6p22-p21; 18q21.2; and 2q32.1). The associated alleles present small odds ratios (the odds of a risk variant being present in cases vs. controls) and suggest causative involvement of gene regulatory mechanisms in SZ. (2) Polygenic inheritance. (3) Involvement of rare (<1%) and large (>100kb) copy number variants (CNVs). (4) A genetic overlap of SZ with autism and with bipolar disorder (BP) challenging the classical clinical classifications. Most new SZ findings (chromosomal regions and genes) have generated new biological leads. These new findings, however, still need to be translated into a better understanding of the underlying biology and into causal mechanisms. Furthermore, a considerable amount of heritability still remains unexplained (missing heritability). Deep resequencing for rare variants and system biology approaches (e.g., integrating DNA sequence and functional data) are expected to further improve our understanding of the genetic architecture of SZ and its underlying biology.

Analysis of prepulse inhibition in mouse lines overexpressing 22q11.2 orthologues

Animal models have been useful in elucidating the genetic basis of the cognitive and behavioural phenotypes associated with the 22q11.2 microdeletions. Loss-of-function models have implicated a number of genes as playing a role in prepulse inhibition (PPI) of the startle response. Here, we report the generation and initial analysis of bacterial artificial chromosome (BAC) transgenic (Tg) mice, overexpressing genes from within the 22q11.2 locus. We used engineered BAC constructs to generate Tg lines and quantitative RT-PCR to assess levels of gene expression in each line. We assessed PPI and open-field activity in mice from two low copy number lines. In Tg-1, a line overexpressing Prodh and Vpreb2, PPI was significantly increased at prepulse levels of 78 dB and 82 dB while no differences were found in activity measures. By contrast, no significant differences were found in PPI testing of the Tg-2 line overexpressing Zdhhc8, Ranbp1, Htf9c, T10, Arvcf and Comt. Taken together with previous loss-of-function reports, these findings suggest that Prodh has a key role in modulating the degree of sensorimotor gating in mice and possibly in humans and provide additional support for an important role of this pathway in modulating behavioural deficits associated with genomic gains or losses at 22q11.2.

Over-expression of a human chromosome 22q11.2 segment including TXNRD2, COMT and ARVCF developmentally affects incentive learning and working memory in mice

Duplication of human chromosome 22q11.2 is associated with elevated rates of mental retardation, autism and many other behavioral phenotypes. However, because duplications cover 1.5-6 Mb, the precise manner in which segments of 22q11.2 causally affect behavior is not known in humans. We have now determined the developmental impact of over-expression of an approximately 190 kb segment of human 22q11.2, which includes the genes TXNRD2, COMT and ARVCF, on behaviors in bacterial artificial chromosome (BAC) transgenic (TG) mice. BAC TG mice and wild-type (WT) mice were tested for their cognitive capacities, affect- and stress-related behaviors and motor activity at 1 and 2 months of age. An enzymatic assay determined the impact of BAC over-expression on the activity level of COMT. BAC TG mice approached a rewarded goal faster (i.e. incentive learning), but were impaired in delayed rewarded alternation during development. In contrast, BAC TG and WT mice were indistinguishable in rewarded alternation without delays, spontaneous alternation, prepulse inhibition, social interaction, anxiety-, stress- and fear-related behaviors and motor activity. Compared with WT mice, BAC TG mice had an approximately 2-fold higher level of COMT activity in the prefrontal cortex, striatum and hippocampus. These data suggest that over-expression of this 22q11.2 segment enhances incentive learning and impairs the prolonged maintenance of working memory, but has no apparent effect on working memory per se, affect- and stress-related behaviors or motor capacity. High copy numbers of this 22q11.2 segment might contribute to a highly selective set of phenotypes in learning and cognition during development.

Sept5 deficiency exerts pleiotropic influence on affective behaviors and cognitive functions in mice

Deletion or duplication of the human chromosome 22q11.2 is associated with many behavioral traits and neuropsychiatric disorders, including autism spectrum disorders and schizophrenia. However, why phenotypes vary widely among individuals with identical deletions or duplications of 22q11.2 and which specific 22q11.2 genes contribute to these phenotypes are still poorly understood. Previous studies have identified a approximately 200 kb 22q11.2 region that contributes to behavioral phenotypes in mice. We tested the role of Septin 5 (Sept5), a gene encoded in the approximately 200 kb region, in affective behaviors, cognitive capacities and motor activity. To evaluate the impact of genetic backgrounds on behavioral phenotypes of Sept5 deficiency, we used mice on two genetic backgrounds. Our data show that Sept5 deficiency decreased affiliative active social interaction, but this phenotypic expression was influenced by genetic backgrounds. In contrast, Sept5 deficiency decreased anxiety-related behavior, increased prepulse inhibition and delayed acquisition of rewarded goal approach, independent of genetic background. These data suggest that Sept5 deficiency exerts pleiotropic effects on a select set of affective behaviors and cognitive processes and that genetic backgrounds could provide an epistatic influence on phenotypic expression.

Design and development of biomimetic quadruped robot for behavior studies of rats and mice

This paper presents the design and development of a novel biomimetic quadruped robot for behavior studies of rats and mice. Many studies have been performed using these animals for the purpose of understanding human mind in psychology, pharmacology and brain science. In these fields, several experiments on social interactions have been performed using rats as basic studies of mental disorders or social learning. However, some researchers mention that the experiments on social interactions using animals are poorly-reproducible. Therefore, we consider that reproducibility of these experiments can be improved by using a robotic agent that interacts with an animal subject. Thus, we developed a small quadruped robot WR-2 (Waseda Rat No. 2) that behaves like a real rat. Proportion and DOF arrangement of WR-2 are designed based on those of a mature rat. This robot has four 3-DOF legs, a 2-DOF waist and a 1-DOF neck. A microcontroller and a wireless communication module are implemented on it. A battery is also implemented. Thus, it can walk, rear by limbs and groom its body.

Failure of neuronal homeostasis results in common neuropsychiatric phenotypes

Failure of normal brain development leads to mental retardation or autism in about 3% of children. Many genes integral to pathways by which synaptic modification and the remodelling of neuronal networks mediate cognitive and social development have been identified, usually through loss of function. Evidence is accumulating, however, that either loss or gain of molecular functions can be deleterious to the nervous system. Copy-number variation, regulation of gene expression by non-coding RNAs and epigenetic changes are all mechanisms by which altered gene dosage can cause the failure of neuronal homeostasis.

Failure to detect the 22q11.2 duplication syndrome rearrangement among patients with schizophrenia

Chromosome aberrations have long been studied in an effort to identify susceptibility genes for schizophrenia. Chromosome 22q11.2 microdeletion is associated with DiGeorge and Velocardiofacial syndromes (DG/VCF) and provides the most convincing evidence of an association between molecular cytogenetic abnormality and schizophrenia. In addition, this region is one of the best replicated linkage findings for schizophrenia. Recently, the reciprocal microduplication on 22q11.2 has been reported as a new syndrome. Preliminary data indicates that individuals with these duplications also suffer from neuropsychiatric disorders. In this study we have investigated the appropriateness of testing schizophrenia patients for the 22q11.2 microduplication. We used multiplex ligation-dependent probe amplification (MLPA) to measure copy number changes on the 22q11.2 region in a sample of 190 patients with schizophrenia. Our results corroborate the prevalence of the 22q11.2 microdeletion in patients with schizophrenia and clinical features of DG/VCFS and do not suggest an association between 22q11.2 microduplication and schizophrenia.

Analysis of TBX1 variation in patients with psychotic and affective disorders

A significant portion of patients with 22q11 deletion syndrome (22q11DS) develop psychiatric disorders, including schizophrenia and other psychotic and affective symptoms, and the responsible gene/s are assumed to also play a significant role in the etiology of nonsyndromic psychiatric disease. The most common psychiatric diagnosis among patients with 22q11DS is schizophrenia, thought to result from neurotransmitter imbalances and also from disturbed brain development. Several genes in the 22q11 region with known or suspected roles in neurotransmitter metabolism have been analyzed in patients with isolated schizophrenia; however, their contribution to the disease remains controversial. Haploinsufficiency of the TBX1 gene has been shown to be sufficient to cause the core physical malformations associated with 22q11DS in mice and humans and via abnormal brain development could contribute to 22q11DS-related and isolated psychiatric disease. 22q11DS populations also have increased rates of psychiatric conditions other than schizophrenia, including mood disorders. We therefore analyzed variations at the TBX1 locus in a cohort of 446 white patients with psychiatric disorders relevant to 22q11DS and 436 ethnically matched controls. The main diagnoses included schizophrenia (n = 226), schizoaffective disorder (n = 67), bipolar disorder (n = 82), and major depressive disorder (n = 29). We genotyped nine tag SNPs in this sample but did not observe significant differences in allele or haplotype frequencies in any of the analyzed groups (all affected, schizophrenia and schizoaffective disorder, schizophrenia alone, and bipolar disorder and major depressive disorder) compared with the control group. Based on these results we conclude that TBX1 variation does not make a strong contribution to the genetic etiology of nonsyndromic forms of psychiatric disorders commonly seen in patients with 22q11DS.

An association study between the genetic polymorphisms within TBX1 and schizophrenia in the Chinese population

The strong association between common psychiatric disorders and the 22q11.2 microdeletion suggests that haploinsufficiency of one or more genes in the region confers susceptibility to these disorders. Recent mouse studies have shown that the T-box 1 (TBX1) gene in the 22q11.2 region can cause prepulse inhibition (PPI) impairment in the heterozygous state. A study has also shown that phenotypic features of 22q11 deletion syndrome (22q11DS) were segregated with an inactivating mutation of TBX1 in one family, suggesting that the TBX1 gene plays a role in the pathogenesis of some psychiatric disorders. We performed an association study between three single nucleotide polymorphisms (SNPs) in the TBX1 gene and schizophrenia. However, we found no significant difference in the genotype or allele distributions between the 328 schizophrenics and 288 controls for any of the polymorphisms, nor was there any haplotype association. Our data suggest that the genetic polymorphisms within TBX1 do not confer an increased susceptibility to schizophrenia in the Chinese population.

Altered motor activity, exploration and anxiety in heterozygous neuregulin 1 mutant mice: implications for understanding schizophrenia

Human genetic studies have shown that neuregulin 1 (NRG1) is a potential susceptibility gene for schizophrenia. Nrg1 influences various neurodevelopmental processes, which are potentially related to schizophrenia. The neurodevelopmental theory of schizophrenia suggests that interactions between genetic and environmental factors are responsible for biochemical alterations leading to schizophrenia. To investigate these interactions and to match experimental design with the pathophysiology of schizophrenia, we applied a comprehensive behavioural phenotyping strategy for motor activity, exploration and anxiety in a heterozygous Nrg1 transmembrane domain mutant mouse model (Nrg1 HET) using different housing conditions and age groups. We observed a locomotion- and exploration-related hyperactive phenotype in Nrg1 HETs. Increased age had a locomotion- and exploration-inhibiting effect, which was significantly attenuated in mutant mice. Environmental enrichment (EE) had a stimulating influence on locomotion and exploration. The impact of EE was more pronounced in Nrg1 hypomorphs. Our study also showed a moderate task-specific anxiolytic-like phenotype for Nrg1 HETs, which was influenced by external factors. The behavioural phenotype detected in heterozygous Nrg1 mutant mice is not specific to schizophrenia per se, but the increased sensitivity of mutant mice to exogenous factors is consistent with the pathophysiology of schizophrenia and the neurodevelopmental theory. Our findings reinforce the importance of carefully controlling experimental designs for external factors and of comprehensive, integrative phenotyping strategies. Thus, Nrg1 HETs may, in combination with other genetic and drug models, help to clarify pathophysiological mechanisms behind schizophrenia.

Analysis of TBX1 variation in patients with psychotic and affective disorders

A significant portion of patients with 22q11 deletion syndrome (22q11DS) develop psychiatric disorders, including schizophrenia and other psychotic and affective symptoms, and the responsible gene/s are assumed to also play a significant role in the etiology of nonsyndromic psychiatric disease. The most common psychiatric diagnosis among patients with 22q11DS is schizophrenia, thought to result from neurotransmitter imbalances and also from disturbed brain development. Several genes in the 22q11 region with known or suspected roles in neurotransmitter metabolism have been analyzed in patients with isolated schizophrenia; however, their contribution to the disease remains controversial. Haploinsufficiency of the TBX1 gene has been shown to be sufficient to cause the core physical malformations associated with 22q11DS in mice and humans and via abnormal brain development could contribute to 22q11DS-related and isolated psychiatric disease. 22q11DS populations also have increased rates of psychiatric conditions other than schizophrenia, including mood disorders. We therefore analyzed variations at the TBX1 locus in a cohort of 446 white patients with psychiatric disorders relevant to 22q11DS and 436 ethnically matched controls. The main diagnoses included schizophrenia (n = 226), schizoaffective disorder (n = 67), bipolar disorder (n = 82), and major depressive disorder (n = 29). We genotyped nine tag SNPs in this sample but did not observe significant differences in allele or haplotype frequencies in any of the analyzed groups (all affected, schizophrenia and schizoaffective disorder, schizophrenia alone, and bipolar disorder and major depressive disorder) compared with the control group. Based on these results we conclude that TBX1 variation does not make a strong contribution to the genetic etiology of nonsyndromic forms of psychiatric disorders commonly seen in patients with 22q11DS.

Non-B DNA conformations, mutagenesis and disease

Recent discoveries have revealed that simple repeating DNA sequences, which are known to adopt non-B DNA conformations (such as triplexes, cruciforms, slipped structures, left-handed Z-DNA and tetraplexes), are mutagenic. The mutagenesis is due to the non-B DNA conformation rather than to the DNA sequence per se in the orthodox right-handed Watson-Crick B-form. The human genetic consequences of these non-B structures are approximately 20 neurological diseases, approximately 50 genomic disorders (caused by gross deletions, inversions, duplications and translocations), and several psychiatric diseases involving polymorphisms in simple repeating sequences. Thus, the convergence of biochemical, genetic and genomic studies has demonstrated a new paradigm implicating the non-B DNA conformations as the mutagenesis specificity determinants, not the sequences as such.

Analyses of the associations between the genes of 22q11 deletion syndrome and schizophrenia

Schizophrenia is a severe, debilitating mental disorder characterized by profound disturbances of cognition, emotion and social functioning. The lifetime morbid risk is surprisingly uniform at slightly less than 1% across different populations and different cultures. The evidence of genetic risk factors is our strongest clue to the cause of schizophrenia. Linkage and association analyses have identified genes associated with the development of schizophrenia. However, most of the alleles or haplotypes identified thus far have only a weak association or are reported to be population specific. A deletion of 22q11.2 that causes the most common microdeletion syndrome (22q11DS) with an estimated prevalence of 1:2,500-1:4,000 live births may represent one of the greatest known genetic risk factors for schizophrenia. Schizophrenia is a late manifestation in approximately 30% of patients with 22q11.2 deletion, comparable to the risk to offspring of two parents with schizophrenia. Clinical and neuroimaging assessments indicate that 22q11DS-schizophrenia is a neurodevelopmental model of schizophrenia. Recent studies have provided evidence that haploinsufficiency of TBX1 is likely to be responsible for many of the physical features associated with the deletion. Most of the genes in the 22q11 deletion region are conserved together on mouse chromosome 16, enabling the generation of mouse models. Similarities in the cardiovascular and other phenotypes between 22q11DS patients and mouse models can provide important insights into roles of genes in neurobehavioral phenotypes. Because more than one gene in the 22q11DS region is likely to contribute to the marked risk for schizophrenia, further extensive studies are necessary. Analyses of 22q11DS will help clarify the molecular pathogenesis of schizophrenia.