Dosage-dependent phenotypes in models of 16p11.2 lesions found in autism

Microduplication of 16p11.2 locus Potentiates Hypertrophic Obesity in Association with Imbalanced Triglyceride Metabolism in White Adipose Tissue

SCOPE

Copy number variation (CNV) of 16p11.2 is a common genetic factor contributing to the etiology of abnormal weight status, while the underlying mechanism is not fully elucidated yet.

METHODS AND RESULTS

The 16p11.2 CNV mouse model with microduplication of the 7Slx1b-Sept1 region (dp/+) is evaluated under normal chow conditions. Compared to the wild type littermates (WT), the dp/+ mice exhibit obvious obese phenotype characterized by significant increase in body mass index, fat pad mass, and fat ratio, with visceral-dominant fat deposits at 12-week age. White adipose tissue (WAT), liver tissue, and plasma are sampled to assess the comorbid metabolic syndrome. In dp/+ mice, histopathologic analyses reveal hypertrophic adipocytes and hepatic steatosis; serological examinations show hyperlipemia and hyperinsulinemia. Further, by comparing lipidomic and transcriptomic profiling of epididymal WAT between dp/+ and WT mice, the study finds the triglyceride (TG) accumulation in dp/+ mice in association with the dysfunction of lipid droplets. Validation of TG-metabolism-associated genes in WAT and in primary cultured adipocytes show enhanced TG synthesis and declined TG hydrolysis in the dp/+ model.

CONCLUSION

This study elucidates that the imbalanced TG synthesis/hydrolysis in adipocytic lipid droplets may contribute to the hypertrophic obesity and metabolic disorders in mice with 16p11.2 microduplication.

Imaging neural circuit pathology of autism spectrum disorders: autism-associated genes, animal models and the application of in vivo two-photon imaging

Recent advances in human genetics identified genetic variants involved in causing autism spectrum disorders (ASDs). Mouse models that mimic mutations found in patients with ASD exhibit behavioral phenotypes consistent with ASD symptoms. These mouse models suggest critical biological factors of ASD etiology. Another important implication of ASD genetics is the enrichment of ASD risk genes in molecules involved in developing synapses and regulating neural circuit function. Sophisticated in vivo imaging technologies applied to ASD mouse models identify common synaptic impairments in the neocortex, with genetic-mutation-specific defects in local neural circuits. In this article, we review synapse- and circuit-level phenotypes identified by in vivo two-photon imaging in multiple mouse models of ASD and discuss the contributions of altered synapse properties and neural circuit activity to ASD pathogenesis.

Inhibition of histone deacetylase 5 ameliorates abnormalities in 16p11.2 duplication mouse model

Microduplication of the human 16p11.2 gene locus is associated with a range of neurodevelopmental outcomes, including autism spectrum disorder (ASD). Mice carrying heterozygous 16p11.2 duplication (16p11.2^dp/+) display social deficits, which is attributable to impaired GABAergic synaptic function in prefrontal cortex (PFC) driven by downregulation of Npas4, an activity-dependent transcription factor that regulates GABA synapse formation. However, the molecular mechanisms underlying the diminished transcription of Npas4 in 16p11.2 duplication remain unknown. Npas4 is one of the target genes regulated by histone deacetylase 5 (HDAC5), an epigenetic enzyme repressing gene expression via removal of transcription-permissive acetyl groups from histones. Here we report that HDAC5 expression is elevated and histone acetylation is reduced at the Npas4 promoter in PFC of 16p11.2^dp/+ mice. Treatment with the HDAC5 inhibitor LMK235 normalizes histone acetylation, restores GABAergic signaling in PFC, and significantly improves social preference in 16p11.2^dp/+ mice. These findings suggest that HDAC5 inhibition is a promising therapeutic avenue to alleviate genetic, synaptic and behavioral deficits in 16p11.2 duplication conditions.

Stride-level analysis of mouse open field behavior using deep-learning-based pose estimation

Gait and posture are often perturbed in many neurological, neuromuscular, and neuropsychiatric conditions. Rodents provide a tractable model for elucidating disease mechanisms and interventions. Here, we develop a neural-network-based assay that adopts the commonly used open field apparatus for mouse gait and posture analysis. We quantitate both with high precision across 62 strains of mice. We characterize four mutants with known gait deficits and demonstrate that multiple autism spectrum disorder (ASD) models show gait and posture deficits, implying this is a general feature of ASD. Mouse gait and posture measures are highly heritable and fall into three distinct classes. We conduct a genome-wide association study to define the genetic architecture of stride-level mouse movement in the open field. We provide a method for gait and posture extraction from the open field and one of the largest laboratory mouse gait and posture data resources for the research community.

Sheppard et al. present a method for gait and posture analysis in the common open field apparatus using neural-network-based pose estimation. They apply this high-throughput method to dissect the genetic architecture of mouse movement.

Social behavior in 16p11.2 and 22q11.2 copy number variations: Insights from mice and humans

Genetic 16p11.2 and 22q11.2 deletions and duplications in humans may alter behavioral developmental trajectories increasing the risk of autism and schizophrenia spectrum disorders, and of attention-deficit/hyperactivity disorder. In this review, we will concentrate on 16p11.2 and 22q11.2 deletions' effects on social functioning, beyond diagnostic categorization. We highlight diagnostic and social sub-constructs discrepancies. Notably, we contrast evidence from human studies with social profiling performed in several mouse models mimicking 16p11.2 and 22q11.2 deletion syndromes. Given the complexity of social behavior, there is a need to assess distinct social processes. This will be important to better understand the biology underlying such genetic-dependent dysfunctions, as well as to give perspective on how therapeutic strategies can be improved. Bridges and divergent points between human and mouse studies are highlighted. Overall, we give challenges and future perspectives to sort the genetics of social heterogeneity.

Brain mapping across 16 autism mouse models reveals a spectrum of functional connectivity subtypes

Autism Spectrum Disorder (ASD) is characterized by substantial, yet highly heterogeneous abnormalities in functional brain connectivity. However, the origin and significance of this phenomenon remain unclear. To unravel ASD connectopathy and relate it to underlying etiological heterogeneity, we carried out a bi-center cross-etiological investigation of fMRI-based connectivity in the mouse, in which specific ASD-relevant mutations can be isolated and modeled minimizing environmental contributions. By performing brain-wide connectivity mapping across 16 mouse mutants, we show that different ASD-associated etiologies cause a broad spectrum of connectional abnormalities in which diverse, often diverging, connectivity signatures are recognizable. Despite this heterogeneity, the identified connectivity alterations could be classified into four subtypes characterized by discrete signatures of network dysfunction. Our findings show that etiological variability is a key determinant of connectivity heterogeneity in ASD, hence reconciling conflicting findings in clinical populations. The identification of etiologically-relevant connectivity subtypes could improve diagnostic label accuracy in the non-syndromic ASD population and paves the way for personalized treatment approaches.

From Neurodevelopmental to Neurodegenerative Disorders: The Vascular Continuum

Structural and functional integrity of the cerebral vasculature ensures proper brain development and function, as well as healthy aging. The inability of the brain to store energy makes it exceptionally dependent on an adequate supply of oxygen and nutrients from the blood stream for matching colossal demands of neural and glial cells. Key vascular features including a dense vasculature, a tightly controlled environment, and the regulation of cerebral blood flow (CBF) all take part in brain health throughout life. As such, healthy brain development and aging are both ensured by the anatomical and functional interaction between the vascular and nervous systems that are established during brain development and maintained throughout the lifespan. During critical periods of brain development, vascular networks remodel until they can actively respond to increases in neural activity through neurovascular coupling, which makes the brain particularly vulnerable to neurovascular alterations. The brain vasculature has been strongly associated with the onset and/or progression of conditions associated with aging, and more recently with neurodevelopmental disorders. Our understanding of cerebrovascular contributions to neurological disorders is rapidly evolving, and increasing evidence shows that deficits in angiogenesis, CBF and the blood-brain barrier (BBB) are causally linked to cognitive impairment. Moreover, it is of utmost curiosity that although neurodevelopmental and neurodegenerative disorders express different clinical features at different stages of life, they share similar vascular abnormalities. In this review, we present an overview of vascular dysfunctions associated with neurodevelopmental (autism spectrum disorders, schizophrenia, Down Syndrome) and neurodegenerative (multiple sclerosis, Huntington's, Parkinson's, and Alzheimer's diseases) disorders, with a focus on impairments in angiogenesis, CBF and the BBB. Finally, we discuss the impact of early vascular impairments on the expression of neurodegenerative diseases.

Novel Molecular Basis for Synapse Formation: Small Non-coding Vault RNA Functions as a Riboregulator of MEK1 to Modulate Synaptogenesis

Small non-coding vault RNAs (vtRNAs) have been described as a component of the vault complex, a hollow-and-barrel-shaped ribonucleoprotein complex found in most eukaryotes. It has been suggested that the function of vtRNAs might not be limited to simply maintaining the structure of the vault complex. Despite the increasing research on vtRNAs, little is known about their physiological functions. Recently, we have shown that murine vtRNA (mvtRNA) up-regulates synaptogenesis by activating the mitogen activated protein kinase (MAPK) signaling pathway. mvtRNA binds to and activates mitogen activated protein kinase 1 (MEK1), and thereby enhances MEK1-mediated extracellular signal-regulated kinase activation. Here, we introduce the regulatory mechanism of MAPK signaling in synaptogenesis by vtRNAs and discuss the possibility as a novel molecular basis for synapse formation.

ERK/MAPK signalling in the developing brain: Perturbations and consequences

The extracellular regulated kinase/microtubule-associated protein kinase (ERK/MAPK) signalling pathway transduces signals that cause an alteration in the ongoing metabolic pathways and modifies gene expression patterns; thus, influencing cellular behaviour. ERK/MAPK signalling is essential for the proper development of the nervous system from neural progenitor cells derived from the embryonic mesoderm. Several signalling molecules that regulate the well-coordinated process of neurodevelopment transduce developmental information through the ERK/MAPK signalling pathway. The ERK/MAPK is a potential novel therapeutic target in several neurodevelopmental disorders, however, despite years of study, there is still significant uncertainty about the exact mechanism by which the ERK/MAPK signalling pathway elicits specific responses in neurodevelopment. Here, we will review the evidence highlighting the role of ERK/MAPK signalling in neurodevelopment. We will also discuss the structural implication and behavioural deficits associated with perturbed ERK/MAPK signalling pathway in cortical development, whilst examining its contribution to the neuropathology of several neurodevelopmental disorders, such as Autism Spectrum Disorder, Schizophrenia, Fragile X, and Attention Deficit Hyperactive Disorder.

Characterizing Sleep Problems in 16p11.2 Deletion and Duplication

Studies of 16p11.2 copy number variants (CNVs) provide an avenue to identify mechanisms of impairment and develop targeted treatments for individuals with neurodevelopmental disorders. 16p11.2 deletion and duplication phenotypes are currently being ascertained; however, sleep disturbances are minimally described. In this study, we examine sleep disturbance in a well-characterized national sample of 16p11.2 CNVs, the Simons Foundation Autism Research Initiative (SFARI) database of youth and adults (n = 692). Factor analyses and multilevel models of derived sleep questionnaires for youth (n = 345) and adults (n = 347) indicate that 16p11.2 carriers show elevated sleep disturbance relative to community controls. Non-carrier family members also show elevated sleep disturbance. However, sleep duration does not differ between carriers and controls. Further studies of sleep in 16p11.2 are needed.

Targeting synaptic plasticity in schizophrenia: insights from genomic studies

Patients with schizophrenia experience cognitive dysfunction and negative symptoms that do not respond to current drug treatments. Historical evidence is consistent with the hypothesis that these deficits are due, at least in part, to altered cortical synaptic plasticity (the ability of synapses to strengthen or weaken their activity), making this an attractive pathway for therapeutic intervention. However, while synaptic transmission and plasticity is well understood in model systems, it has been challenging to identify specific therapeutic targets for schizophrenia. New information is emerging from genomic findings, which converge on synaptic plasticity and provide a new window on the neurobiology of schizophrenia. Translating this information into therapeutic advances will require a multidisciplinary and collaborative approach.

Sex-Specific Stress-Related Behavioral Phenotypes and Central Amygdala Dysfunction in a Mouse Model of 16p11.2 Microdeletion

Background

Substantial evidence indicates that a microdeletion on human chromosome 16p11.2 is linked to neurodevelopmental disorders, including autism spectrum disorder (ASD). Carriers of this deletion show divergent symptoms besides the core features of autism spectrum disorder, such as anxiety and emotional symptoms. The neural mechanisms underlying these symptoms are poorly understood.

Methods

We used mice heterozygous for a deletion allele of the genomic region corresponding to the human 16p11.2 microdeletion locus (i.e., 16p11.2 del/+ mice) and their sex-matched wild-type littermates for the study and examined their anxiety-related behaviors, auditory perception, and central amygdala circuit function using behavioral, circuit tracing, and electrophysiological techniques.

Results

Mice heterozygous for a deletion allele of the genomic region corresponding to the human 16p11.2 microdeletion locus (i.e., 16p11.2 del/+ mice) had sex-specific anxiety-related behavioral and neural circuit changes. Specifically, we found that female, but not male, 16p11.2 del/+ mice showed enhanced fear generalization-a hallmark of anxiety disorders-after auditory fear conditioning and displayed increased anxiety-like behaviors after physical restraint stress. Notably, such sex-specific behavioral changes were paralleled by an increase in activity in central amygdala neurons projecting to the globus pallidus in female, but not male, 16p11.2 del/+ mice.

Conclusions

Together, these results reveal female-specific anxiety phenotypes related to 16p11.2 microdeletion syndrome and a potential underlying neural circuit mechanism. Our study therefore identifies previously underappreciated sex-specific behavioral and neural changes in a genetic model of 16p11.2 microdeletion syndrome and highlights the importance of investigating female-specific aspects of this syndrome for targeted treatment strategies.

Reversal of synaptic and behavioral deficits in a 16p11.2 duplication mouse model via restoration of the GABA synapse regulator Npas4

The human 16p11.2 gene locus is a hot spot for copy number variations, which predispose carriers to a range of neuropsychiatric phenotypes. Microduplications of 16p11.2 are associated with autism spectrum disorder (ASD), intellectual disability (ID), and schizophrenia (SZ). Despite the debilitating nature of 16p11.2 duplications, the underlying molecular mechanisms remain poorly understood. Here we performed a comprehensive behavioral characterization of 16p11.2 duplication mice (16p11.2^dp/+) and identified social and cognitive deficits reminiscent of ASD and ID phenotypes. 16p11.2^dp/+ mice did not exhibit the SZ-related sensorimotor gating deficits, psychostimulant-induced hypersensitivity, or motor impairment. Electrophysiological recordings of 16p11.2^dp/+ mice found deficient GABAergic synaptic transmission and elevated neuronal excitability in the prefrontal cortex (PFC), a brain region critical for social and cognitive functions. RNA-sequencing identified genome-wide transcriptional aberrance in the PFC of 16p11.2^dp/+ mice, including downregulation of the GABA synapse regulator Npas4. Restoring Npas4 expression in PFC of 16p11.2^dp/+ mice ameliorated the social and cognitive deficits and reversed GABAergic synaptic impairment and neuronal hyperexcitability. These findings suggest that prefrontal cortical GABAergic synaptic circuitry and Npas4 are strongly implicated in 16p11.2 duplication pathology, and may represent potential targets for therapeutic intervention in ASD.

16p11.2 deletion is associated with hyperactivation of human iPSC-derived dopaminergic neuron networks and is rescued by RHOA inhibition in vitro

Reciprocal copy number variations (CNVs) of 16p11.2 are associated with a wide spectrum of neuropsychiatric and neurodevelopmental disorders. Here, we use human induced pluripotent stem cells (iPSCs)-derived dopaminergic (DA) neurons carrying CNVs of 16p11.2 duplication (16pdup) and 16p11.2 deletion (16pdel), engineered using CRISPR-Cas9. We show that 16pdel iPSC-derived DA neurons have increased soma size and synaptic marker expression compared to isogenic control lines, while 16pdup iPSC-derived DA neurons show deficits in neuronal differentiation and reduced synaptic marker expression. The 16pdel iPSC-derived DA neurons have impaired neurophysiological properties. The 16pdel iPSC-derived DA neuronal networks are hyperactive and have increased bursting in culture compared to controls. We also show that the expression of RHOA is increased in the 16pdel iPSC-derived DA neurons and that treatment with a specific RHOA-inhibitor, Rhosin, rescues the network activity of the 16pdel iPSC-derived DA neurons. Our data suggest that 16p11.2 deletion-associated iPSC-derived DA neuron hyperactivation can be rescued by RHOA inhibition.

Neurological consequences of neurovascular unit and brain vasculature damages: potential risks for pregnancy infections and COVID-19-babies

Intragravidic and perinatal infections, acting through either direct viral effect or immune-mediated responses, are recognized causes of liability for neurodevelopmental disorders in the progeny. The large amounts of epidemiological data and the wealth of information deriving from animal models of gestational infections have contributed to delineate, in the last years, possible underpinning mechanisms for this phenomenon, including defects in neuronal migration, impaired spine and synaptic development, and altered activation of microglia. Recently, dysfunctions of the neurovascular unit and anomalies of the brain vasculature have unexpectedly emerged as potential causes at the origin of behavioral abnormalities and psychiatric disorders consequent to prenatal and perinatal infections. This review aims to discuss the up-to-date literature evidence pointing to the neurovascular unit and brain vasculature damages as the etiological mechanisms in neurodevelopmental syndromes. We focus on the inflammatory events consequent to intragravidic viral infections as well as on the direct viral effects as the potential primary triggers. These authors hope that a timely review of the literature will help to envision promising research directions, also relevant for the present and future COVID-19 longitudinal studies.

16p11 Duplication Disrupts Hippocampal-Orbitofrontal-Amygdala Connectivity, Revealing a Neural Circuit Endophenotype for Schizophrenia

Chromosome 16p11.2 duplications dramatically increase risk for schizophrenia, but the mechanisms remain largely unknown. Here, we show that mice with an equivalent genetic mutation (16p11.2 duplication mice) exhibit impaired hippocampal-orbitofrontal and hippocampal-amygdala functional connectivity. Expression of schizophrenia-relevant GABAergic cell markers (parvalbumin and calbindin) is selectively decreased in orbitofrontal cortex, while somatostatin expression is decreased in lateral amygdala. When 16p11.2 duplication mice are tested in cognitive tasks dependent on hippocampal-orbitofrontal connectivity, performance is impaired in an 8-arm maze "N-back" working memory task and in a touchscreen continuous performance task. Consistent with hippocampal-amygdala dysconnectivity, deficits in ethologically relevant social behaviors are also observed. Overall, the cellular/molecular, brain network, and behavioral alterations markedly mirror those observed in schizophrenia patients. Moreover, the data suggest that 16p11.2 duplications selectively impact hippocampal-amygdaloid-orbitofrontal circuitry, supporting emerging ideas that dysfunction in this network is a core element of schizophrenia and defining a neural circuit endophenotype for the disease.

Targeted genome editing in vivo corrects a Dmd duplication restoring wild-type dystrophin expression

Tandem duplication mutations are increasingly found to be the direct cause of many rare heritable diseases, accounting for up to 10% of cases. Unfortunately, animal models recapitulating such mutations are scarce, limiting our ability to study them and develop genome editing therapies. Here, we describe the generation of a novel duplication mouse model, harboring a multi-exonic tandem duplication in the Dmd gene which recapitulates a human mutation. Duplication correction of this mouse was achieved by implementing a single-guide RNA (sgRNA) CRISPR/Cas9 approach. This strategy precisely removed a duplication mutation in vivo, restored full-length dystrophin expression, and was accompanied by improvements in both histopathological and clinical phenotypes. We conclude that CRISPR/Cas9 represents a powerful tool to accurately model and treat tandem duplication mutations. Our findings will open new avenues of research for exploring the study and therapeutics of duplication disorders.

Transcriptomic networks implicate neuronal energetic abnormalities in three mouse models harboring autism and schizophrenia-associated mutations

Genetic risk for psychiatric illness is complex, so identification of shared molecular pathways where distinct forms of genetic risk might coincide is of substantial interest. A growing body of genetic and genomic studies suggest that such shared molecular pathways exist across disorders with different clinical presentations, such as schizophrenia and autism spectrum disorder (ASD). But how this relates to specific genetic risk factors is unknown. Further, whether some of the molecular changes identified in brain relate to potentially confounding antemortem or postmortem factors are difficult to prove. We analyzed the transcriptome from the cortex and hippocampus of three mouse lines modeling human copy number variants (CNVs) associated with schizophrenia and ASD: Df(h15q13)/+, Df(h22q11)/+, and Df(h1q21)/+ which carry the 15q13.3 deletion, 22q11.2 deletion, and 1q21.1 deletion, respectively. Although we found very little overlap of differential expression at the level of individual genes, gene network analysis identified two cortical and two hippocampal modules of co-expressed genes that were dysregulated across all three mouse models. One cortical module was associated with neuronal energetics and firing rate, and overlapped with changes identified in postmortem human brain from SCZ and ASD patients. These data highlight aspects of convergent gene expression in mouse models harboring major risk alleles, and strengthen the connection between changes in neuronal energetics and neuropsychiatric disorders in humans.

Distinct Basal Metabolism in Three Mouse Models of Neurodevelopmental Disorders

Prevalence of metabolic disturbances is higher among individuals with neurodevelopmental disorders (NDDs), yet this association has been largely overlooked. Investigation into human disease remains challenging, as a complete pathophysiological understanding relies on accurate modeling and highly controlled variables. Genetically engineered mouse models are widely used to gain insight into the biology of human NDDs, but research focus has been on behavioral and neurophysiological abnormalities. Such models not only allow for evaluating usefulness in reproducing human features, including similarities and discrepancies with rodent phenotypes, but they also represent a unique opportunity to observe and quantify novel anomalies. Here, we present the first characterization and comparison of basal metabolism in three mouse models of NDDs, namely, Down syndrome (DS; Dp(16)Yey/+ mice), 16p11.2 deletion syndrome (16pDel; 16p11.2^df/+ mice), and fragile X syndrome [FXS; Fmr1 knock-out (KO) mice] and their wild-type (WT) counterparts. Using the Comprehensive Lab Animal Monitoring System (CLAMS) coupled to EchoMRI, as well as quantification of key plasma metabolites by liquid chromatography mass spectrometry (LC-MS), our in vivo study reveals that each mouse model expresses a unique metabolic signature that is sex-specific, independent of the amount of food consumed and minimally influenced by physical activity. In particular, we identify striking differences in body composition, respiratory exchange ratio (RER), caloric expenditure (CE), and concentrations of circulating plasma metabolites related to mitochondrial function. Providing novel insight into NDD-associated metabolic alterations is an essential prerequisite for future preclinical and clinical interventions.

Expression of Genes in the 16p11.2 Locus during Development of the Human Fetal Cerebral Cortex

The 593 kbp 16p11.2 copy number variation (CNV) affects the gene dosage of 29 protein coding genes, with heterozygous 16p11.2 microduplication or microdeletion implicated in about 1% of autism spectrum disorder (ASD) cases. The 16p11.2 CNV is frequently associated with macrocephaly or microcephaly indicating early defects of neurogenesis may contribute to subsequent ASD symptoms, but it is unknown which 16p11.2 transcripts are expressed in progenitors and whose levels are likely, therefore, to influence neurogenesis. Analysis of human fetal gene expression data revealed that KIF22, ALDOA, HIRIP3, PAGR1, and MAZ transcripts are expressed in neural progenitors with ALDOA and KIF22 significantly enriched compared to post-mitotic cells. To investigate the possible roles of ALDOA and KIF22 proteins in human cerebral cortex development we used immunohistochemical staining to describe their expression in late first and early second trimester human cerebral cortex. KIF22 protein is restricted to proliferating cells with its levels increasing during the cell cycle and peaking at mitosis. ALDOA protein is expressed in all cell types and does not vary with cell-cycle phase. Our expression analysis suggests the hypothesis that altered neurogenesis in the cerebral cortex contributes to ASD in 16p11.2 CNV patients.

Neural Mechanisms Underlying Repetitive Behaviors in Rodent Models of Autism Spectrum Disorders

Autism spectrum disorder (ASD) is comprised of several conditions characterized by alterations in social interaction, communication, and repetitive behaviors. Genetic and environmental factors contribute to the heterogeneous development of ASD behaviors. Several rodent models display ASD-like phenotypes, including repetitive behaviors. In this review article, we discuss the potential neural mechanisms involved in repetitive behaviors in rodent models of ASD and related neuropsychiatric disorders. We review signaling pathways, neural circuits, and anatomical alterations in rodent models that display robust stereotypic behaviors. Understanding the mechanisms and circuit alterations underlying repetitive behaviors in rodent models of ASD will inform translational research and provide useful insight into therapeutic strategies for the treatment of repetitive behaviors in ASD and other neuropsychiatric disorders.

Targeting the RHOA pathway improves learning and memory in adult Kctd13 and 16p11.2 deletion mouse models

Background

Gene copy number variants play an important role in the occurrence of neurodevelopmental disorders. Particularly, the deletion of the 16p11.2 locus is associated with autism spectrum disorder, intellectual disability, and several other features. Earlier studies highlighted the implication of Kctd13 genetic imbalance in 16p11.2 deletion through the regulation of the RHOA pathway.

Methods

Here, we generated a new mouse model with a small deletion of two key exons in Kctd13. Then, we targeted the RHOA pathway to rescue the cognitive phenotypes of the Kctd13 and 16p11.2 deletion mouse models in a pure genetic background. We used a chronic administration of fasudil (HA1077), an inhibitor of the Rho-associated protein kinase, for six weeks in mouse models carrying a heterozygous inactivation of Kctd13, or the deletion of the entire 16p11.2 BP4-BP5 homologous region.

Results

We found that the small Kctd13 heterozygous deletion induced a cognitive phenotype similar to the whole deletion of the 16p11.2 homologous region, in the Del/+ mice. We then showed that chronic fasudil treatment can restore object recognition memory in adult heterozygous mutant mice for Kctd13 and for 16p11.2 deletion. In addition, learning and memory improvement occurred in parallel to change in the RHOA pathway.

Limitations

The Kcdt13 mutant line does not recapitulate all the phenotypes found in the 16p11.2 Del/+ model. In particular, the locomotor activity was not altered at 12 and 18 weeks of age and the object location memory was not defective in 18-week old mutants. Similarly, the increase in locomotor activity was not modified by the treatment in the 16p11.2 Del/+ mouse model, suggesting that other loci were involved in such defects. Rescue was observed only after four weeks of treatment but no long-term experiment has been carried out so far. Finally, we did not check the social behaviour, which requires working in another hybrid genetic background.

Conclusion

These findings confirm KCTD13 as one target gene causing cognitive deficits in 16p11.2 deletion patients, and the relevance of the RHOA pathway as a therapeutic path for 16p11.2 deletion. In addition, they reinforce the contribution of other gene(s) involved in cognitive defects found in the 16p11.2 models in older mice.

Cortical organoids model early brain development disrupted by 16p11.2 copy number variants in autism

Reciprocal deletion and duplication of the 16p11.2 region is the most common copy number variation (CNV) associated with autism spectrum disorders. We generated cortical organoids from skin fibroblasts of patients with 16p11.2 CNV to investigate impacted neurodevelopmental processes. We show that organoid size recapitulates macrocephaly and microcephaly phenotypes observed in the patients with 16p11.2 deletions and duplications. The CNV dosage affects neuronal maturation, proliferation, and synapse number, in addition to its effect on organoid size. We demonstrate that 16p11.2 CNV alters the ratio of neurons to neural progenitors in organoids during early neurogenesis, with a significant excess of neurons and depletion of neural progenitors observed in deletions. Transcriptomic and proteomic profiling revealed multiple pathways dysregulated by the 16p11.2 CNV, including neuron migration, actin cytoskeleton, ion channel activity, synaptic-related functions, and Wnt signaling. The level of the active form of small GTPase RhoA was increased in both, deletions and duplications. Inhibition of RhoA activity rescued migration deficits, but not neurite outgrowth. This study provides insights into potential neurobiological mechanisms behind the 16p11.2 CNV during neocortical development.

Sleep Duration in Mouse Models of Neurodevelopmental Disorders

Sleep abnormalities are common in patients with neurodevelopmental disorders, and it is thought that deficits in sleep may contribute to the unfolding of symptoms in these disorders. Appreciating sleep abnormalities in neurodevelopmental disorders could be important for designing a treatment for these disorders. We studied sleep duration in three mouse models by means of home-cage monitoring: Tsc2^+/- (tuberous sclerosis complex), oxytocin receptor (Oxtr) knockout (KO) (autism spectrum disorders), and Shank3 ^e4-9 KO (Phelan-McDermid syndrome). We studied both male and female mice, and data were analyzed to examine effects of both genotype and sex. In general, we found that female mice slept less than males regardless of genotype or phase. We did not find any differences in sleep duration in either Tsc2^+/- or Oxtr KO mice, compared to controls. In Shank3 ^e4-9 KO mice, we found a statistically significant genotype x phase interaction (p = 0.002) with a trend that Shank3^e4-9 KO mice regardless of sex slept more than control mice in the active phase. Our results have implications for the management of patients with Phelan-McDermid syndrome.

Rare Pathogenic Copy Number Variation in the 16p11.2 (BP4-BP5) Region Associated with Neurodevelopmental and Neuropsychiatric Disorders: A Review of the Literature

Copy number variants (CNVs) play an important role in the genetic underpinnings of neuropsychiatric/neurodevelopmental disorders. The chromosomal region 16p11.2 (BP4-BP5) harbours both deletions and duplications that are associated in carriers with neurodevelopmental and neuropsychiatric conditions as well as several rare disorders including congenital malformation syndromes. The aim of this article is to provide a review of the current knowledge of the diverse neurodevelopmental disorders (NDD) associated with 16p11.2 deletions and duplications reported in published cohorts. A literature review was conducted using the PubMed/MEDLINE electronic database limited to papers published in English between 1 January 2010 and 31 July 2020, describing 16p11.2 deletions and duplications carriers' cohorts. Twelve articles meeting inclusion criteria were reviewed from the 75 articles identified by the search. Of these twelve papers, eight described both deletions and duplications, three described deletions only and one described duplications only. This study highlights the heterogeneity of NDD descriptions of the selected cohorts and inconsistencies concerning accuracy of data reporting.

Cortico-basal ganglia circuits underlying dysfunctional control of motor behaviors in neuropsychiatric disorders

Neuropsychiatric disorders often manifest with abnormal control of motor behavior. Common symptoms include restricted and repetitive patterns of behavior (RRBs). Cortico-basal ganglia circuits have been implicated in the etiology of RBBs. However, there is a vast range of behaviors encompassed in RRBs, from simple explosive motor tics to rather complex ritualized compulsions. In this review, we highlight how recent findings about the function of specific basal ganglia circuits can begin to shed light into defined motor symptoms associated with neuropsychiatric disorders. We discuss recent studies using genetic animal models that advocate that different aspects of motor repetition in neurodevelopmental disorders, like obsessive-compulsive disorder and autism spectrum disorder, emerge from particular dysregulations in distinct cortico-basal ganglia circuits.

BDNF and JNK Signaling Modulate Cortical Interneuron and Perineuronal Net Development: Implications for Schizophrenia-Linked 16p11.2 Duplication Syndrome

Schizophrenia (SZ) is a neurodevelopmental disorder caused by the interaction of genetic and environmental risk factors. One of the strongest genetic risk variants is duplication (DUP) of chr.16p11.2. SZ is characterized by cortical gamma-amino-butyric acid (GABA)ergic interneuron dysfunction and disruption to surrounding extracellular matrix structures, perineuronal nets (PNNs). Developmental maturation of GABAergic interneurons, and also the resulting closure of the critical period of cortical plasticity, is regulated by brain-derived neurotrophic factor (BDNF), although the mechanisms involved are unknown. Here, we show that BDNF promotes GABAergic interneuron and PNN maturation through JNK signaling. In mice reproducing the 16p11.2 DUP, where the JNK upstream activator Taok2 is overexpressed, we find that JNK is overactive and there are developmental abnormalities in PNNs, which persist into adulthood. Prefrontal cortex parvalbumin (PVB) expression is reduced, while PNN intensity is increased. Additionally, we report a unique role for TAOK2 signaling in the regulation of PVB interneurons. Our work implicates TAOK2-JNK signaling in cortical interneuron and PNN development, and in the responses to BDNF. It also demonstrates that over-activation of this pathway in conditions associated with SZ risk causes long-lasting disruption in cortical interneurons.

16p11.2 Copy Number Variations and Neurodevelopmental Disorders

Copy number variations (CNVs) of the human 16p11.2 genetic locus are associated with a range of neurodevelopmental disorders, including autism spectrum disorder, intellectual disability, and epilepsy. In this review, we delineate genetic information and diverse phenotypes in individuals with 16p11.2 CNVs, and synthesize preclinical findings from transgenic mouse models of 16p11.2 CNVs. Mice with 16p11.2 deletions or duplications recapitulate many core behavioral phenotypes, including social and cognitive deficits, and exhibit altered synaptic function across various brain areas. Mechanisms of transcriptional dysregulation and cortical maldevelopment are reviewed, along with potential therapeutic intervention strategies.

A standardized social preference protocol for measuring social deficits in mouse models of autism

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by social communication deficits and other behavioral abnormalities. The three-chamber social preference test is often used to assess social deficits in mouse models of ASD. However, varying and often contradicting phenotypic descriptions of ASD mouse models can be found in the scientific literature, and the substantial variability in the methods used by researchers to assess social deficits in mice could be a contributing factor. Here we describe a standardized three-chamber social preference protocol, which is sensitive and reliable at detecting social preference deficits in several mouse models of ASD. This protocol comprises three phases that can all be completed within 1 d. The test mouse is first habituated to the apparatus containing two empty cups in the side chambers, followed by the pre-test phase in which the mouse can interact with two identical inanimate objects placed in the cups. During the test phase, the mouse is allowed to interact with a social stimulus (an unfamiliar wild-type (WT) mouse) contained in one cup and a novel non-social stimulus contained in the other cup. The protocol is thus designed to assess preference between social and non-social stimuli under conditions of equal salience. The broad implementation of the three-chamber social preference protocol presented here should improve the accuracy and consistency of assessments for social preference deficits associated with ASD and other psychiatric disorders.

Comprehensive Behavioral Phenotyping of a 16p11.2 Del Mouse Model for Neurodevelopmental Disorders

The microdeletion of copy number variant 16p11.2 is one of the most common genetic mutations associated with neurodevelopmental disorders, such as Autism Spectrum Disorders (ASDs). Here, we describe our comprehensive behavioral phenotyping of the 16p11.2 deletion line developed by Alea Mills on a C57BL/6J and 129S1/SvImJ F1 background (Del^m ). Male and female Del^m mice were tested in developmental milestones as preweanlings (PND2-PND12), and were tested in open field activity, elevated zero maze, rotarod, novel object recognition, fear conditioning, social approach, and other measures during post-weaning (PND21), adolescence (PND42), and adulthood (>PND70). Developmentally, Del^m mice show distinct weight reduction that persists into adulthood. Del^m males also have reduced grasp reflexes and limb strength during development, but no other reflexive deficits whereas Del^m females show limb strength deficits and decreased sensitivity to heat. In a modified version of a rotarod task that measures balance and coordinated motor activity, Del^m males, but not females, show improved performance at high speeds. Del^m males and females also show age-specific reductions in anxiety-like behavior compared with WTs, but neither sex show deficits in a social preference task. When assessing learning and memory, Del^m males and females show age-specific impairments in a novel object or spatial object recognition, but no deficits in contextual fear memory. This work extends the understanding of the behavioral phenotypes seen with 16p11.2 deletion by emphasizing age and sex-specific deficits; important variables to consider when studying mouse models for neurodevelopmental disorders. LAY SUMMARY: Autism spectrum disorder is a common neurodevelopmental disorder that causes repetitive behavior and impairments in social interaction and communication. Here, we assess the effects of one of the most common genetic alterations in ASDs, a deletion of one copy of 29 genes, using a mouse model. These animals show differences in behavior between males and females and across ages compared with control animals, including changes in development, cognition, and motor coordination. Autism Res 2020, 13: 1670-1684. © 2020 International Society for Autism Research and Wiley Periodicals LLC.

Dysfunctional d-aspartate metabolism in BTBR mouse model of idiopathic autism

BACKGROUND

Autism spectrum disorders (ASD) comprise a heterogeneous group of neurodevelopmental conditions characterized by impairment in social interaction, deviance in communication, and repetitive behaviors. Dysfunctional ionotropic NMDA and AMPA receptors, and metabotropic glutamate receptor 5 activity at excitatory synapses has been recently linked to multiple forms of ASD. Despite emerging evidence showing that d-aspartate and d-serine are important neuromodulators of glutamatergic transmission, no systematic investigation on the occurrence of these D-amino acids in preclinical ASD models has been carried out.

METHODS

Through HPLC and qPCR analyses we investigated d-aspartate and d-serine metabolism in the brain and serum of four ASD mouse models. These include BTBR mice, an idiopathic model of ASD, and Cntnap2^-/-, Shank3^-/-, and 16p11.2^+/- mice, three established genetic mouse lines recapitulating high confidence ASD-associated mutations.

RESULTS

Biochemical and gene expression mapping in Cntnap2^-/-, Shank3^-/-, and 16p11.2^+/- failed to find gross cerebral and serum alterations in d-aspartate and d-serine metabolism. Conversely, we found a striking and stereoselective increased d-aspartate content in the prefrontal cortex, hippocampus and serum of inbred BTBR mice. Consistent with biochemical assessments, in the same brain areas we also found a robust reduction in mRNA levels of d-aspartate oxidase, encoding the enzyme responsible for d-aspartate catabolism.

CONCLUSIONS

Our results demonstrated the presence of disrupted d-aspartate metabolism in a widely used animal model of idiopathic ASD.

GENERAL SIGNIFICANCE

Overall, this work calls for a deeper investigation of D-amino acids in the etiopathology of ASD and related developmental disorders.

Drug-responsive autism phenotypes in the 16p11.2 deletion mouse model: a central role for gene-environment interactions

There are no current treatments for autism, despite its high prevalence. Deletions of chromosome 16p11.2 dramatically increase risk for autism, suggesting that mice with an equivalent genetic rearrangement may offer a valuable model for the testing of novel classes of therapeutic drug. 16p11.2 deletion (16p11.2 DEL) mice and wild-type controls were assessed using an ethological approach, with 24 h monitoring of activity and social interaction of groups of mice in a home-cage environment. The ability of the excitation/inhibition modulator N-acetyl cysteine (NAC) and the 5-HT_1B/1D/1F receptor agonist eletriptan to normalise the behavioural deficits observed was tested. 16p11.2 DEL mice exhibited largely normal behaviours, but, following the stress of an injection, showed hyperlocomotion, reduced sociability, and a strong anxiolytic phenotype. The hyperactivity and reduced sociability, but not the suppressed anxiety, were effectively attenuated by both NAC and eletriptan. The data suggest that 16p11.2 DEL mice show an autism-relevant phenotype that becomes overt after an acute stressor, emphasising the importance of gene-environmental interactions in phenotypic analysis. Further, they add to an emerging view that NAC, or 5-HT_1B/1D/1F receptor agonist treatment, may be a promising strategy for further investigation as a future treatment.

Vascular contributions to 16p11.2 deletion autism syndrome modeled in mice

While the neuronal underpinnings of autism spectrum disorder (ASD) are being unraveled, vascular contributions to ASD remain elusive. Here, we investigated postnatal cerebrovascular development in the 16p11.2^df/+ mouse model of 16p11.2 deletion ASD syndrome. We discover that 16p11.2 hemizygosity leads to male-specific, endothelium-dependent structural and functional neurovascular abnormalities. In 16p11.2^df/+ mice, endothelial dysfunction results in impaired cerebral angiogenesis at postnatal day 14, and in altered neurovascular coupling and cerebrovascular reactivity at postnatal day 50. Moreover, we show that there is defective angiogenesis in primary 16p11.2^df/+ mouse brain endothelial cells and in induced-pluripotent-stem-cell-derived endothelial cells from human carriers of the 16p11.2 deletion. Finally, we find that mice with an endothelium-specific 16p11.2 deletion (16p11.2^ΔEC) partially recapitulate some of the behavioral changes seen in 16p11.2 syndrome, specifically hyperactivity and impaired motor learning. By showing that developmental 16p11.2 haploinsufficiency from endothelial cells results in neurovascular and behavioral changes in adults, our results point to a potential role for endothelial impairment in ASD.

Mouse model systems of autism spectrum disorder: Replicability and informatics signature

Phenotyping mouse model systems of human disease has proven to be a difficult task, with frequent poor inter- and intra-laboratory replicability, particularly in behavioral domains such as social and cognitive function. However, establishing robust animal model systems with strong construct validity is of fundamental importance as they are central tools for understanding disease pathophysiology and developing therapeutics. To complete our studies of mouse model systems relevant to autism spectrum disorder (ASD), we present a replication of the main findings from our two published studies of five genetic mouse model systems of ASD. To assess the intra-laboratory robustness of previous results, we chose the two model systems that showed the greatest phenotypic differences, the Shank3/F and Cntnap2, and repeated assessments of general health, activity and social behavior. We additionally explored all five model systems in the same framework, comparing all results obtained in this three-yearlong effort using informatics techniques to assess commonalities and differences. Our results showed high intra-laboratory replicability of results, even for those with effect sizes that were not particularly large, suggesting that discrepancies in the literature may be dependent on subtle but pivotal differences in testing conditions, housing enrichment, or background strains and less so on the variability of the behavioral phenotypes. The overall informatics analysis suggests that in our behavioral assays we can separate the set of tested mouse model system into two main classes that in some aspects lie on opposite ends of the behavioral spectrum, supporting the view that autism is not a unitary concept.

Drosophila models of pathogenic copy-number variant genes show global and non-neuronal defects during development

While rare pathogenic copy-number variants (CNVs) are associated with both neuronal and non-neuronal phenotypes, functional studies evaluating these regions have focused on the molecular basis of neuronal defects. We report a systematic functional analysis of non-neuronal defects for homologs of 59 genes within ten pathogenic CNVs and 20 neurodevelopmental genes in Drosophila melanogaster. Using wing-specific knockdown of 136 RNA interference lines, we identified qualitative and quantitative phenotypes in 72/79 homologs, including 21 lines with severe wing defects and six lines with lethality. In fact, we found that 10/31 homologs of CNV genes also showed complete or partial lethality at larval or pupal stages with ubiquitous knockdown. Comparisons between eye and wing-specific knockdown of 37/45 homologs showed both neuronal and non-neuronal defects, but with no correlation in the severity of defects. We further observed disruptions in cell proliferation and apoptosis in larval wing discs for 23/27 homologs, and altered Wnt, Hedgehog and Notch signaling for 9/14 homologs, including AATF/Aatf, PPP4C/Pp4-19C, and KIF11/Klp61F. These findings were further supported by tissue-specific differences in expression patterns of human CNV genes, as well as connectivity of CNV genes to signaling pathway genes in brain, heart and kidney-specific networks. Our findings suggest that multiple genes within each CNV differentially affect both global and tissue-specific developmental processes within conserved pathways, and that their roles are not restricted to neuronal functions.

Rare copy-number variants (CNVs), or large deletions and duplications in the genome, are associated with both neuronal and non-neuronal clinical features. Previous functional studies for these disorders have primarily focused on understanding the cellular mechanisms for neurological and behavioral phenotypes. To understand how genes within these CNVs contribute to developmental defects in non-neuronal tissues, we assessed 79 homologs of CNV and known neurodevelopmental genes in Drosophila models. We found that most homologs showed developmental defects when knocked down in the adult fly wing, ranging from mild size changes to severe wrinkled wings or lethality. Although a majority of tested homologs showed defects when knocked down specifically in wings or eyes, we found no correlation in the severity of the observed defects in these two tissues. A subset of the homologs showed disruptions in cellular processes in the developing fly wing, including alterations in cell proliferation, apoptosis, and cellular signaling pathways. Furthermore, human CNV genes also showed differences in gene expression patterns and interactions with signaling pathway genes across multiple human tissues. Our findings suggest that genes within CNV disorders affect global developmental processes in both neuronal and non-neuronal tissues.

Increased TBX6 gene dosages induce congenital cervical vertebral malformations in humans and mice

BACKGROUND

Congenital vertebral malformations (CVMs) manifest with abnormal vertebral morphology. Genetic factors have been implicated in CVM pathogenesis, but the underlying pathogenic mechanisms remain unclear in most subjects. We previously reported that the human 16p11.2 BP4-BP5 deletion and its associated TBX6 dosage reduction caused CVMs. We aim to investigate the reciprocal 16p11.2 BP4-BP5 duplication and its potential genetic contributions to CVMs.

METHODS AND RESULTS

Patients who were found to carry the 16p11.2 BP4-BP5 duplication by chromosomal microarray analysis were retrospectively analysed for their vertebral phenotypes. The spinal assessments in seven duplication carriers showed that four (57%) presented characteristics of CVMs, supporting the contention that increased TBX6 dosage could induce CVMs. For further in vivo functional investigation in a model organism, we conducted genome editing of the upstream regulatory region of mouse Tbx6 using CRISPR-Cas9 and obtained three mouse mutant alleles (Tbx6up1 to Tbx6up3 ) with elevated expression levels of Tbx6. Luciferase reporter assays showed that the Tbx6up3 allele presented with the 160% expression level of that observed in the reference (+) allele. Therefore, the homozygous Tbx6up3/up3 mice could functionally mimic the TBX6 dosage of heterozygous carriers of 16p11.2 BP4-BP5 duplication (approximately 150%, ie, 3/2 gene dosage of the normal level). Remarkably, 60% of the Tbx6up3/up3 mice manifested with CVMs. Consistent with our observations in humans, the CVMs induced by increased Tbx6 dosage in mice mainly affected the cervical vertebrae.

CONCLUSION

Our findings in humans and mice consistently support that an increased TBX6 dosage contributes to the risk of developing cervical CVMs.

Zebrafish as a tool to study schizophrenia-associated copy number variants

Schizophrenia remains one of the most debilitating human neurodevelopmental disorders, with few effective treatments and striking consequences felt by individuals, communities and society as a whole. As such, there remains a critical need for further investigation into the mechanistic underpinnings of schizophrenia so that novel therapeutic targets can be identified. Because schizophrenia is a highly heritable disorder, genetic risk factors remain an attractive avenue for this research. Given their clear molecular genetic consequences, recurrent microdeletions and duplications, or copy number variants (CNVs), represent one of the most tractable genetic entry points to elucidating these mechanisms. To date, eight CNVs have been shown to significantly increase the risk of schizophrenia. Although rodent models of these CNVs that exhibit behavioral phenotypes have been generated, the underlying molecular mechanisms remain largely elusive. Over the past decades, the zebrafish has emerged as a powerful vertebrate model that has led to fundamental discoveries in developmental neurobiology and behavioral genetics. Here, we review the attributes that make zebrafish exceptionally well suited to investigating individual and combinatorial gene contributions to CNV-mediated brain dysfunction in schizophrenia. With highly conserved genetics and neural substrates, an ever-expanding molecular genetic and imaging toolkit, and ability to perform high-throughput and high-content genetic and pharmacologic screens, zebrafish is poised to generate deep insights into the molecular genetic mechanisms of schizophrenia-associated neurodevelopmental and behavioral deficits, and to facilitate the identification of therapeutic targets.

The abiding relevance of mouse models of rare mutations to psychiatric neuroscience and therapeutics

Studies using powerful family-based designs aided by large scale case-control studies, have been instrumental in cracking the genetic complexity of the disease, identifying rare and highly penetrant risk mutations and providing a handle on experimentally tractable model systems. Mouse models of rare mutations, paired with analysis of homologous cognitive and sensory processing deficits and state-of-the-art neuroscience methods to manipulate and record neuronal activity have started providing unprecedented insights into pathogenic mechanisms and building the foundation of a new biological framework for understanding mental illness. A number of important principles are emerging, namely that degradation of the computational mechanisms underlying the ordered activity and plasticity of both local and long-range neuronal assemblies, the building blocks necessary for stable cognition and perception, might be the inevitable consequence and the common point of convergence of the vastly heterogeneous genetic liability, manifesting as defective internally- or stimulus-driven neuronal activation patterns and triggering the constellation of schizophrenia symptoms. Animal models of rare mutations have the unique potential to help us move from "which" (gene) to "how", "where" and "when" computational regimes of neural ensembles are affected. Linking these variables should improve our understanding of how symptoms emerge and how diagnostic boundaries are established at a circuit level. Eventually, a better understanding of pathophysiological trajectories at the level of neural circuitry in mice, aided by basic human experimental biology, should guide the development of new therapeutics targeting either altered circuitry itself or the underlying biological pathways.

Altered sleep architecture, rapid eye movement sleep, and neural oscillation in a mouse model of human chromosome 16p11.2 microdeletion

Sleep abnormalities are common among children with neurodevelopmental disorders. The human chr16p11.2 microdeletion is associated with a range of neurological and neurobehavioral abnormalities. Previous studies of a mouse model of human chr16p11.2 microdeletion (chr16p11.2df/+) have demonstrated pathophysiological changes at the synapses in the hippocampus and striatum; however, the impact of this genetic abnormality on system level brain functions, such as sleep and neural oscillation, has not been adequately investigated. Here, we show that chr16p11.2df/+ mice have altered sleep architecture, with increased wake time and reduced time in rapid eye movement (REM) and non-REM (NREM) sleep. Importantly, several measurements of REM sleep are significantly changed in deletion mice. The REM bout number and the bout number ratio of REM to NREM are decreased in mutant mice, suggesting a deficit in REM-NREM transition. The average REM bout duration is shorter in mutant mice, indicating a defect in REM maintenance. In addition, whole-cell patch clamp recording of the ventrolateral periaqueductal gray (vlPAG)-projecting gamma-aminobutyric acid (GABA)ergic neurons in the lateral paragigantocellular nucleus of ventral medulla of mutant mice reveal that these neurons, which are important for NREM-REM transition and REM maintenance, have hyperpolarized resting membrane potential and increased membrane resistance. These changes in intrinsic membrane properties suggest that these projection-specific neurons of mutant mice are less excitable, and thereby may play a role in deficient NREM-REM transition and REM maintenance. Furthermore, mutant mice exhibit changes in neural oscillation involving multiple frequency classes in several vigilance states. The most significant alterations occur in the theta frequency during wake and REM sleep.

The Human-Specific BOLA2 Duplication Modifies Iron Homeostasis and Anemia Predisposition in Chromosome 16p11.2 Autism Individuals

Human-specific duplications at chromosome 16p11.2 mediate recurrent pathogenic 600 kbp BP4-BP5 copy-number variations, which are among the most common genetic causes of autism. These copy-number polymorphic duplications are under positive selection and include three to eight copies of BOLA2, a gene involved in the maturation of cytosolic iron-sulfur proteins. To investigate the potential advantage provided by the rapid expansion of BOLA2, we assessed hematological traits and anemia prevalence in 379,385 controls and individuals who have lost or gained copies of BOLA2: 89 chromosome 16p11.2 BP4-BP5 deletion carriers and 56 reciprocal duplication carriers in the UK Biobank. We found that the 16p11.2 deletion is associated with anemia (18/89 carriers, 20%, p = 4e-7, OR = 5), particularly iron-deficiency anemia. We observed similar enrichments in two clinical 16p11.2 deletion cohorts, which included 6/63 (10%) and 7/20 (35%) unrelated individuals with anemia, microcytosis, low serum iron, or low blood hemoglobin. Upon stratification by BOLA2 copy number, our data showed an association between low BOLA2 dosage and the above phenotypes (8/15 individuals with three copies, 53%, p = 1e-4). In parallel, we analyzed hematological traits in mice carrying the 16p11.2 orthologous deletion or duplication, as well as Bola2^+/- and Bola2^-/- animals. The Bola2-deficient mice and the mice carrying the deletion showed early evidence of iron deficiency, including a mild decrease in hemoglobin, lower plasma iron, microcytosis, and an increased red blood cell zinc-protoporphyrin-to-heme ratio. Our results indicate that BOLA2 participates in iron homeostasis in vivo, and its expansion has a potential adaptive role in protecting against iron deficiency.

Oligogenic Effects of 16p11.2 Copy-Number Variation on Craniofacial Development

A copy-number variant (CNV) of 16p11.2 encompassing 30 genes is associated with developmental and psychiatric disorders, head size, and body mass. The genetic mechanisms that underlie these associations are not understood. To determine the influence of 16p11.2 genes on development, we investigated the effects of CNV on craniofacial structure in humans and model organisms. We show that deletion and duplication of 16p11.2 have "mirror" effects on specific craniofacial features that are conserved between human and rodent models of the CNV. By testing dosage effects of individual genes on the shape of the mandible in zebrafish, we identify seven genes with significant effects individually and find evidence for others when genes were tested in combination. The craniofacial phenotypes of 16p11.2 CNVs represent a model for studying the effects of genes on development, and our results suggest that the associated facial gestalts are attributable to the combined effects of multiple genes.

Autism Spectrum Disorder-Related Syndromes: Modeling with Drosophila and Rodents

Whole exome analyses have identified a number of genes associated with autism spectrum disorder (ASD) and ASD-related syndromes. These genes encode key regulators of synaptogenesis, synaptic plasticity, cytoskeleton dynamics, protein synthesis and degradation, chromatin remodeling, transcription, and lipid homeostasis. Furthermore, in silico studies suggest complex regulatory networks among these genes. Drosophila is a useful genetic model system for studies of ASD and ASD-related syndromes to clarify the in vivo roles of ASD-associated genes and the complex gene regulatory networks operating in the pathogenesis of ASD and ASD-related syndromes. In this review, we discuss what we have learned from studies with vertebrate models, mostly mouse models. We then highlight studies with Drosophila models. We also discuss future developments in the related field.

Genetic Causes and Modifiers of Autism Spectrum Disorder

Autism Spectrum Disorder (ASD) is one of the most prevalent neurodevelopmental disorders, affecting an estimated 1 in 59 children. ASD is highly genetically heterogeneous and may be caused by both inheritable and de novo gene variations. In the past decade, hundreds of genes have been identified that contribute to the serious deficits in communication, social cognition, and behavior that patients often experience. However, these only account for 10-20% of ASD cases, and patients with similar pathogenic variants may be diagnosed on very different levels of the spectrum. In this review, we will describe the genetic landscape of ASD and discuss how genetic modifiers such as copy number variation, single nucleotide polymorphisms, and epigenetic alterations likely play a key role in modulating the phenotypic spectrum of ASD patients. We also consider how genetic modifiers can alter convergent signaling pathways and lead to impaired neural circuitry formation. Lastly, we review sex-linked modifiers and clinical implications. Further understanding of these mechanisms is crucial for both comprehending ASD and for developing novel therapies.

Targeting Peripheral Somatosensory Neurons to Improve Tactile-Related Phenotypes in ASD Models

Somatosensory over-reactivity is common among patients with autism spectrum disorders (ASDs) and is hypothesized to contribute to core ASD behaviors. However, effective treatments for sensory over-reactivity and ASDs are lacking. We found distinct somatosensory neuron pathophysiological mechanisms underlie tactile abnormalities in different ASD mouse models and contribute to some ASD-related behaviors. Developmental loss of ASD-associated genes Shank3 or Mecp2 in peripheral mechanosensory neurons leads to region-specific brain abnormalities, revealing links between developmental somatosensory over-reactivity and the genesis of aberrant behaviors. Moreover, acute treatment with a peripherally restricted GABAA receptor agonist that acts directly on mechanosensory neurons reduced tactile over-reactivity in six distinct ASD models. Chronic treatment of Mecp2 and Shank3 mutant mice improved body condition, some brain abnormalities, anxiety-like behaviors, and some social impairments but not memory impairments, motor deficits, or overgrooming. Our findings reveal a potential therapeutic strategy targeting peripheral mechanosensory neurons to treat tactile over-reactivity and select ASD-related behaviors.

Behavioral neuroscience of autism

Autism spectrum disorder (ASD) is a neurodevelopmental disorder. Several genetic causes of ASD have been identified and this has enabled researchers to construct mouse models. Mouse behavioral tests reveal impaired social interaction and communication, as well as increased repetitive behavior and behavioral inflexibility in these mice, which correspond to core behavioral deficits observed in individuals with ASD. However, the connection between these behavioral abnormalities and the underlying dysregulation in neuronal circuits and synaptic function is poorly understood. Moreover, different components of the ASD phenotype may be linked to dysfunction in different brain regions, making it even more challenging to chart the pathophysiological mechanisms involved in ASD. Here we summarize the research on mouse models of ASD and their contribution to understanding pathophysiological mechanisms. Specifically, we emphasize abnormal serotonin production and regulation, as well as the disruption in circadian rhythms and sleep that are observed in a subset of ASD, and propose that spatiotemporal disturbances in brainstem development may be a primary cause of ASD that propagates towards the cerebral cortex.

Kctd13-deficient mice display short-term memory impairment and sex-dependent genetic interactions

The 16p11.2 BP4-BP5 deletion and duplication syndromes are associated with a complex spectrum of neurodevelopmental phenotypes that includes developmental delay and autism spectrum disorder, with a reciprocal effect on head circumference, brain structure and body mass index. Mouse models of the 16p11.2 copy number variant have recapitulated some of the patient phenotypes, while studies in flies and zebrafish have uncovered several candidate contributory genes within the region, as well as complex genetic interactions. We evaluated one of these loci, KCTD13, by modeling haploinsufficiency and complete knockout in mice. In contrast to the zebrafish model, and in agreement with recent data, we found normal brain structure in heterozygous and homozygous mutants. However, recapitulating previously observed genetic interactions, we discovered sex-specific brain volumetric alterations in double heterozygous Kctd13xMvp and Kctd13xLat mice. Behavioral testing revealed a significant deficit in novel object recognition, novel location recognition and social transmission of food preference in Kctd13 mutants. These phenotypes were concomitant with a reduction in density of mature spines in the hippocampus, but potentially independent of RhoA abundance, which was unperturbed postnatally in our mutants. Furthermore, transcriptome analyses from cortex and hippocampus highlighted the dysregulation of pathways important in neurodevelopment, the most significant of which was synaptic formation. Together, these data suggest that KCTD13 contributes to the neurocognitive aspects of patients with the BP4-BP5 deletion, likely through genetic interactions with other loci.

Refining the Phenotype of Recurrent Rearrangements of Chromosome 16

Chromosome 16 is one of the most gene-rich chromosomes of our genome, and 10% of its sequence consists of segmental duplications, which give instability and predisposition to rearrangement by the recurrent mechanism of non-allelic homologous recombination. Microarray technologies have allowed for the analysis of copy number variations (CNVs) that can contribute to the risk of developing complex diseases. By array comparative genomic hybridization (CGH) screening of 1476 patients, we detected 27 cases with CNVs on chromosome 16. We identified four smallest regions of overlapping (SROs): one at 16p13.11 was found in seven patients; one at 16p12.2 was found in four patients; two close SROs at 16p11.2 were found in twelve patients; finally, six patients were found with atypical rearrangements. Although phenotypic variability was observed, we identified a male bias for Childhood Apraxia of Speech associated to 16p11.2 microdeletions. We also reported an elevated frequency of second-site genomic alterations, supporting the model of the second hit to explain the clinical variability associated with CNV syndromes. Our goal was to contribute to the building of a chromosome 16 disease-map based on disease susceptibility regions. The role of the CNVs of chromosome 16 was increasingly made clear in the determination of developmental delay. We also found that in some cases a second-site CNV could explain the phenotypic heterogeneity by a simple additive effect or a pejorative synergistic effect.

Shank3 Transgenic and Prenatal Zinc-Deficient Autism Mouse Models Show Convergent and Individual Alterations of Brain Structures in MRI

Research efforts over the past decades have unraveled both genetic and environmental factors, which contribute to the development of autism spectrum disorders (ASD). It is, to date, largely unknown how different underlying causes result in a common phenotype. However, the individual course of development and the different comorbidities might reflect the heterogeneous genetic and non-genetic contributions. Therefore, it is reasonable to identify commonalities and differences in models of these disorders at the different hierarchical levels of brain function, including genetics/environment, cellular/synaptic functions, brain regions, connectivity, and behavior. To that end, we investigated Shank3 transgenic mouse lines and compared them with a prenatal zinc-deficient (PZD) mouse model of ASD at the level of brain structural alterations in an 11,7 T small animal magnetic resonance imaging (MRI). Animals were measured at 4 and 9 weeks of age. We identified a decreased total brain volume (TBV) and hippocampal size of Shank3^−/− mice but a convergent increase of basal ganglia (striatum and globus pallidus) in most mouse lines. Moreover, Shank3 transgenic mice had smaller thalami, whereas PZD mice had this region enlarged. Intriguingly, Shank3 heterozygous knockout mice mostly showed minor abnormalities to full knockouts, which might reflect the importance of proper Shank3 dosage in neuronal cells. Most reported volume changes seemed to be more pronounced at younger age. Our results indicate both convergent and divergent brain region abnormalities in genetic and non-genetic models of ASD. These alterations of brain structures might be mirrored in the reported behavior of both models, which have not been assessed in this study.

Home-cage hypoactivity in mouse genetic models of autism spectrum disorder

Genome-wide association and whole exome sequencing studies from Autism Spectrum Disorder (ASD) patient populations have implicated numerous risk factor genes whose mutation or deletion results in significantly increased incidence of ASD. Behavioral studies of monogenic mutant mouse models of ASD-associated genes have been useful for identifying aberrant neural circuitry. However, behavioral results often differ from lab to lab, and studies incorporating both males and females are often not performed despite the significant sex-bias of ASD. In this study, we sought to investigate the simple, passive behavior of home-cage activity monitoring across multiple 24-h days in four different monogenic mouse models of ASD: Shank3b^-/-, Cntnap2^-/-, Pcdh10^+/-, and Fmr1 knockout mice. Relative to sex-matched wildtype (WT) littermates, we discovered significant home-cage hypoactivity, particularly in the dark (active) phase of the light/dark cycle, in male mice of all four ASD-associated transgenic models. For Cntnap2^-/- and Pcdh10^+/- mice, these activity alterations were sex-specific, as female mice did not exhibit home-cage activity differences relative to sex-matched WT controls. These home-cage hypoactivity alterations differ from activity findings previously reported using short-term activity measurements in a novel open field. Despite circadian problems reported in human ASD patients, none of the mouse models studied had alterations in free-running circadian period. Together, these findings highlight a shared phenotype across several monogenic mouse models of ASD, outline the importance of methodology on behavioral interpretation, and in some genetic lines parallel the male-enhanced phenotypic presentation observed in human ASDs.