Hippocampal Pruning as a New Theory of Schizophrenia Etiopathogenesis

Future avenues in Drosophila mushroom body research

How does the brain translate sensory information into complex behaviors? With relatively small neuronal numbers, readable behavioral outputs, and an unparalleled genetic toolkit, the Drosophila mushroom body (MB) offers an excellent model to address this question in the context of associative learning and memory. Recent technological breakthroughs, such as the freshly completed full-brain connectome, multiomics approaches, CRISPR-mediated gene editing, and machine learning techniques, led to major advancements in our understanding of the MB circuit at the molecular, structural, physiological, and functional levels. Despite significant progress in individual MB areas, the field still faces the fundamental challenge of resolving how these different levels combine and interact to ultimately control the behavior of an individual fly. In this review, we discuss various aspects of MB research, with a focus on the current knowledge gaps, and an outlook on the future methodological developments required to reach an overall view of the neurobiological basis of learning and memory.

Modeling gene × environment interactions in PTSD using human neurons reveals diagnosis-specific glucocorticoid-induced gene expression

Post-traumatic stress disorder (PTSD) can develop following severe trauma, but the extent to which genetic and environmental risk factors contribute to individual clinical outcomes is unknown. Here, we compared transcriptional responses to hydrocortisone exposure in human induced pluripotent stem cell (hiPSC)-derived glutamatergic neurons and peripheral blood mononuclear cells (PBMCs) from combat veterans with PTSD (n = 19 hiPSC and n = 20 PBMC donors) and controls (n = 20 hiPSC and n = 20 PBMC donors). In neurons only, we observed diagnosis-specific glucocorticoid-induced changes in gene expression corresponding with PTSD-specific transcriptomic patterns found in human postmortem brains. We observed glucocorticoid hypersensitivity in PTSD neurons, and identified genes that contribute to this PTSD-dependent glucocorticoid response. We find evidence of a coregulated network of transcription factors that mediates glucocorticoid hyper-responsivity in PTSD. These findings suggest that induced neurons represent a platform for examining the molecular mechanisms underlying PTSD, identifying biomarkers of stress response, and conducting drug screening to identify new therapeutics.

Spatiotemporal Control of Neuronal Remodeling by Cell Adhesion Molecules: Insights From Drosophila

Developmental neuronal remodeling is required for shaping the precise connectivity of the mature nervous system. Remodeling involves pruning of exuberant neural connections, often followed by regrowth of adult-specific ones, as a strategy to refine neural circuits. Errors in remodeling are associated with neurodevelopmental disorders such as schizophrenia and autism. Despite its fundamental nature, our understanding of the mechanisms governing neuronal remodeling is far from complete. Specifically, how precise spatiotemporal control of remodeling and rewiring is achieved is largely unknown. In recent years, cell adhesion molecules (CAMs), and other cell surface and secreted proteins of various families, have been implicated in processes of neurite pruning and wiring specificity during circuit reassembly. Here, we review some of the known as well as speculated roles of CAMs in these processes, highlighting recent advances in uncovering spatiotemporal aspects of regulation. Our focus is on the fruit fly Drosophila, which is emerging as a powerful model in the field, due to the extensive, well-characterized and stereotypic remodeling events occurring throughout its nervous system during metamorphosis, combined with the wide and constantly growing toolkit to identify CAM binding and resulting cellular interactions in vivo. We believe that its many advantages pose Drosophila as a leading candidate for future breakthroughs in the field of neuronal remodeling in general, and spatiotemporal control by CAMs specifically.

SARS-CoV-2-associated cytokine storm during pregnancy as a possible risk factor for neuropsychiatric disorder development in post-pandemic infants

A strong association between perinatal viral infections and neurodevelopmental disorders has been established. Both the direct contact of the virus with the developing brain and the strong maternal immune response originated by viral infections can impair proper neurodevelopment. Coronavirus disease 2019 (COVID-19), caused by the highly-infectious severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is currently responsible for a large global outbreak and is a major public health issue. While initial studies focused on the viral impact on the respiratory system, increasing evidence suggest that SARS-CoV-2 infects other organs and tissues including the mature brain. While studies continue to determine the neuropathology associated to COVID-19, the consequences of SARS-CoV-2 infection to the developing brain remain largely unexplored. The present review discusses evidence suggesting that SARS-CoV-2 infection may have persistent effects on the course of pregnancy and on brain development. Studies have shown that several proinflammatory mediators which are increased in the SARS-CoV-2-associated cytokine storm, are also modified in other viral infections known to increase the risk of neurodevelopmental disorders. In this sense, further studies should assess the genuine effects of SARS-CoV-2 infection during pregnancy and delivery along with an extended follow-up of the offspring, including neurocognitive, neuroimaging, and electrophysiological examination. It also remains to be determined whether and by which mechanisms SARS-CoV-2 intrauterine and early life infection could lead to an increased risk of developing neuropsychiatric disorders, such as autism (ASD) and schizophrenia (SZ), in the offspring.

Dysregulation of synaptic pruning as a possible link between intestinal microbiota dysbiosis and neuropsychiatric disorders

The prenatal and early postnatal stages represent a critical time window for human brain development. Interestingly, this window partly overlaps with the maturation of the intestinal flora (microbiota) that play a critical role in the bidirectional communication between the central and the enteric nervous systems (microbiota-gut-brain axis). The microbial composition has important influences on general health and the development of several organ systems, such as the gastrointestinal tract, the immune system, and also the brain. Clinical studies have shown that microbiota alterations are associated with a wide range of neuropsychiatric disorders including autism spectrum disorder, attention deficit hyperactivity disorder, schizophrenia, and bipolar disorder. In this review, we dissect the link between these neuropsychiatric disorders and the intestinal microbiota by focusing on their effect on synaptic pruning, a vital process in the maturation and establishing efficient functioning of the brain. We discuss in detail how synaptic pruning is dysregulated differently in the aforementioned neuropsychiatric disorders and how it can be influenced by dysbiosis and/or changes in the intestinal microbiota composition. We also review that the improvement in the intestinal microbiota composition by a change in diet, probiotics, prebiotics, or fecal microbiota transplantation may play a role in improving neuropsychiatric functioning, which can be at least partly explained via the optimization of synaptic pruning and neuronal connections. Altogether, the demonstration of the microbiota's influence on brain function via microglial-induced synaptic pruning addresses the possibility that the manipulation of microbiota-immune crosstalk represents a promising strategy for treating neuropsychiatric disorders.

With a little help from my friends: how intercellular communication shapes neuronal remodeling

Developmental neuronal remodeling shapes the mature connectivity of the nervous system in both vertebrates and invertebrates. Remodeling often combines degenerative and regenerative events, and defects in its normal progression have been linked to neurological disorders. Here we review recent progress that highlights the roles of cell-cell interactions during remodeling. We propose that these are fundamental to elucidating how spatiotemporal control of remodeling and coordinated circuit remodeling are achieved. We cover examples spanning various neuronal circuits in vertebrates and invertebrates and involving interactions between neurons and different cell types.

CRMP2 mediates Sema3F-dependent axon pruning and dendritic spine remodeling

Regulation of axon guidance and pruning of inappropriate synapses by class 3 semaphorins are key to the development of neural circuits. Collapsin response mediator protein 2 (CRMP2) has been shown to regulate axon guidance by mediating semaphorin 3A (Sema3A) signaling; however, nothing is known about its role in synapse pruning. Here, using newly generated crmp2^-/- mice we demonstrate that CRMP2 has a moderate effect on Sema3A-dependent axon guidance in vivo, and its deficiency leads to a mild defect in axon guidance in peripheral nerves and the corpus callosum. Surprisingly, crmp2^-/- mice display prominent defects in stereotyped axon pruning in hippocampus and visual cortex and altered dendritic spine remodeling, which is consistent with impaired Sema3F signaling and with models of autism spectrum disorder (ASD). We demonstrate that CRMP2 mediates Sema3F signaling in primary neurons and that crmp2^-/- mice display ASD-related social behavior changes in the early postnatal period as well as in adults. Together, we demonstrate that CRMP2 mediates Sema3F-dependent synapse pruning and its dysfunction shares histological and behavioral features of ASD.

Basic Symptoms Are Associated With Age in Patients With a Clinical High-Risk State for Psychosis: Results From the PRONIA Study

In community studies, both attenuated psychotic symptoms (APS) and basic symptoms (BS) were more frequent but less clinically relevant in children and adolescents compared to adults. In doing so, they displayed differential age thresholds that were around age 16 for APS, around age 18 for perceptive BS, and within the early twenties for cognitive BS. Only the age effect has previously been studied and replicated in clinical samples for APS. Thus, we examined the reported age effect on and age thresholds of 14 criteria-relevant BS in a patient sample at clinical-high risk of psychosis (N = 261, age 15-40 yrs.), recruited within the European multicenter PRONIA-study. BS and the BS criteria, "Cognitive Disturbances" (COGDIS) and "Cognitive-perceptive BS" (COPER), were assessed with the "Schizophrenia Proneness Instrument, Adult version" (SPI-A). Using logistic regressions, prevalence rates of perceptive and cognitive BS, and of COGDIS and COPER, as well as the impact of social and role functioning on the association between age and BS were studied in three age groups (15-18 years, 19-23 years, 24-40 years). Most patients (91.2%) reported any BS, 55.9% any perceptive and 87.4% any cognitive BS. Furthermore, 56.3% met COGDIS and 80.5% COPER. Not exhibiting the reported differential age thresholds, both perceptive and cognitive BS, and, at trend level only, COPER were less prevalent in the oldest age group (24-40 years); COGDIS was most frequent in the youngest group (15-18 years). Functional deficits did not better explain the association with age, particularly in perceptive BS and cognitive BS meeting the frequency requirement of BS criteria. Our findings broadly confirmed an age threshold in BS and, thus, the earlier assumed link between presence of BS and brain maturation processes. Yet, age thresholds of perceptive and cognitive BS did not differ. This lack of differential age thresholds might be due to more pronounced the brain abnormalities in this clinical sample compared to earlier community samples. These might have also shown in more frequently occurring and persistent BS that, however, also resulted from a sampling toward these, i.e., toward COGDIS. Future studies should address the neurobiological basis of CHR criteria in relation to age.

Age effects on basic symptoms in the community: A route to gain new insight into the neurodevelopment of psychosis?

Reports of limited clinical significance of attenuated psychotic symptoms before age 15/16 indicate an important role of neurodevelopment in the early detection of psychoses. Therefore, we examined if age also exerts an influence on the prevalence and clinical significance of the 14 cognitive and perceptive basic symptoms (BS) used in psychosis-risk criteria and conceptualized as the most direct self-experienced expression of neurobiological aberrations. A random representative general population sample of the Swiss canton Bern (N = 689, age 8-40 years, 06/2011-05/2014) was interviewed for BS, psychosocial functioning, and current mental disorder. BS were reported by 18% of participants, mainly cognitive BS (15%). In regression analyses, age affected perceptive and cognitive BS differently, indicating an age threshold for perceptive BS in late adolescence (around age 18) and for cognitive BS in young adulthood (early twenties)-with higher prevalence, but a lesser association with functional deficits and the presence of mental disorder in the below-threshold groups. Thereby, interaction effects between age and BS on functioning and mental disorder were commonly stronger than individual effects of age and BS. Indicating support of the proposed "substrate-closeness" of BS, differential age effects of perceptual and cognitive BS seem to follow normal brain maturation processes, in which they might occur as infrequent and temporary non-pathological disturbances. Their persistence or occurrence after conclusion of main brain maturation processes, however, might signify aberrant maturation or neurodegenerative processes. Thus, BS might provide important insight into the pathogenesis of psychosis and into differential neuroprotective or anti-inflammatory targets.

Neuropsychiatric phenotype in relation to gene variants in the hemizygous allele in 3q29 deletion carriers: A case series

Background

Genetic risk variants in the hemizygous allele may influence neuropsychiatric manifestations and clinical course in 3q29 deletion carriers.

Methods

In‐depth phenotypic assessment in two deletion carriers included medical records, medical, genetic, psychiatric and neuropsychological evaluations, brain MRI scan and EEG. Blood samples were analyzed for copy number variations, and deep sequencing of the affected 3q29 region was performed in patients and seven first‐degree relatives. Risk variants were identified through bioinformatic analysis.

Results

One deletion carrier was diagnosed with learning difficulties and childhood autism, the other with mild intellectual disability and schizophrenia. EEG abnormalities in childhood normalized in adulthood in both. Cognitive abilities improved during adolescence in one deletion carrier. Both had microcytic, hypochromic erythrocytes and suffered from chronic pain and fatigue. Molecular and bioinformatic analyses identified risk variants in the hemizygous allele that were not present in the homozygous state in relatives in genes involved in cilia function and insulin action in the autistic individual and in synaptic function and neurosteroid transport in the subject with schizophrenia.

Conclusion

3q29 deletion carriers may undergo developmental phenotypic transition and need regular medical follow‐up. Identified risk variants in the remaining hemizygous allele should be explored further in autism and schizophrenia research.

Combining Developmental and Perturbation-Seq Uncovers Transcriptional Modules Orchestrating Neuronal Remodeling

Developmental neuronal remodeling is an evolutionarily conserved mechanism required for precise wiring of nervous systems. Despite its fundamental role in neurodevelopment and proposed contribution to various neuropsychiatric disorders, the underlying mechanisms are largely unknown. Here, we uncover the fine temporal transcriptional landscape of Drosophila mushroom body γ neurons undergoing stereotypical remodeling. Our data reveal rapid and dramatic changes in the transcriptional landscape during development. Focusing on DNA binding proteins, we identify eleven that are required for remodeling. Furthermore, we sequence developing γ neurons perturbed for three key transcription factors required for pruning. We describe a hierarchical network featuring positive and negative feedback loops. Superimposing the perturbation-seq on the developmental expression atlas highlights a framework of transcriptional modules that together drive remodeling. Overall, this study provides a broad and detailed molecular insight into the complex regulatory dynamics of developmental remodeling and thus offers a pipeline to dissect developmental processes via RNA profiling.

Developmental Coordination during Olfactory Circuit Remodeling in Drosophila

Developmental neuronal remodeling is crucial for proper wiring of the adult nervous system. While remodeling of individual neuronal populations has been studied, how neuronal circuits remodel-and whether remodeling of synaptic partners is coordinated-is unknown. We found that the Drosophila anterior paired lateral (APL) neuron undergoes stereotypic remodeling during metamorphosis in a similar time frame as the mushroom body (MB) ɣ-neurons, with whom it forms a functional circuit. By simultaneously manipulating both neuronal populations, we found that cell-autonomous inhibition of ɣ-neuron pruning resulted in the inhibition of APL pruning in a process that is mediated, at least in part, by Ca²⁺-Calmodulin and neuronal activity dependent interaction. Finally, ectopic unpruned MB ɣ axons display ectopic connections with the APL, as well as with other neurons, at the adult, suggesting that inhibiting remodeling of one neuronal type can affect the functional wiring of the entire micro-circuit.

Association of Hippocampal Atrophy With Duration of Untreated Psychosis and Molecular Biomarkers During Initial Antipsychotic Treatment of First-Episode Psychosis

IMPORTANCE

Duration of untreated psychosis (DUP) has been associated with poor outcomes in schizophrenia, but the mechanism responsible for this association is not known.

OBJECTIVES

To determine whether hippocampal volume loss occurs during the initial 8 weeks of antipsychotic treatment and whether it is associated with DUP, and to examine molecular biomarkers in association with hippocampal volume loss and DUP.

DESIGN, SETTING, AND PARTICIPANTS

A naturalistic longitudinal study with matched healthy controls was conducted at Shanghai Mental Health Center. Between March 5, 2013, and October 8, 2014, 71 medication-naive individuals with nonaffective first-episode psychosis (FEP) and 73 age- and sex-matched healthy controls were recruited. After approximately 8 weeks, 31 participants with FEP and 32 controls were reassessed.

EXPOSURES

The participants with FEP were treated according to standard clinical practice with second-generation antipsychotics.

MAIN OUTCOMES AND MEASURES

Hippocampal volumetric integrity (HVI) (an automated estimate of the parenchymal fraction in a standardized hippocampal volume of interest), DUP, 13 peripheral molecular biomarkers, and 14 single-nucleotide polymorphisms from 12 candidate genes were determined.

RESULTS

The full sample consisted of 71 individuals with FEP (39 women and 32 men; mean [SD] age, 25.2 [7.7] years) and 73 healthy controls (40 women and 33 men; mean [SD] age, 23.9 [6.4] years). Baseline median left HVI was lower in the FEP group (n = 57) compared with the controls (n = 54) (0.9275 vs 0.9512; difference in point estimate, -0.020 [95% CI, -0.029 to -0.010]; P = .001). During approximately 8 weeks of antipsychotic treatment, left HVI decreased in 24 participants with FEP at a median annualized rate of -.03791 (-4.1% annualized change from baseline) compared with an increase of 0.00115 (0.13% annualized change from baseline) in 31 controls (difference in point estimate, -0.0424 [95% CI, -0.0707 to -0.0164]; P = .001). The change in left HVI was inversely associated with DUP (r = -0.61; P = .002). Similar results were found for right HVI, although the association between change in right HVI and DUP did not achieve statistical significance (r = -0.35; P = .10). Exploratory analyses restricted to the left HVI revealed an association between left HVI and markers of inflammation, oxidative stress, brain-derived neurotrophic factor, glial injury, and markers reflecting dopaminergic and glutamatergic transmission.

CONCLUSIONS AND RELEVANCE

An association between longer DUP and accelerated hippocampal atrophy during initial treatment suggests that psychosis may have persistent, possibly deleterious, effects on brain structure. Additional studies are needed to replicate these exploratory findings of molecular mechanisms by which untreated psychosis may affect hippocampal volume and to determine whether these effects account for the known association between longer DUP and poor outcome.

Shep regulates Drosophila neuronal remodeling by controlling transcription of its chromatin targets

Neuronal remodeling is crucial for formation of the mature nervous system and disruption of this process can lead to neuropsychiatric diseases. Global gene expression changes in neurons during remodeling as well as the factors that regulate these changes remain poorly defined. To elucidate this process, we performed RNA-seq on isolated Drosophila larval and pupal neurons and found upregulated synaptic signaling and downregulated gene expression regulators as a result of normal neuronal metamorphosis. We further tested the role of alan shepard (shep), which encodes an evolutionarily conserved RNA-binding protein required for proper neuronal remodeling. Depletion of shep in neurons prevents the execution of metamorphic gene expression patterns, and shep-regulated genes correspond to Shep chromatin and/or RNA-binding targets. Reduced expression of a Shep-inhibited target gene that we identified, brat, is sufficient to rescue neuronal remodeling defects of shep knockdown flies. Our results reveal direct regulation of transcriptional programs by Shep to regulate neuronal remodeling during metamorphosis.

Searching for ancient balanced polymorphisms shared between Neanderthals and Modern Humans

Hominin evolution is characterized by adaptive solutions often rooted in behavioral and cognitive changes. If balancing selection had an important and long-lasting impact on the evolution of these traits, it can be hypothesized that genes associated with them should carry an excess of shared polymorphisms (trans- SNPs) across recent Homo species. In this study, we investigate the role of balancing selection in human evolution using available exomes from modern (Homo sapiens) and archaic humans (H. neanderthalensis and Denisovan) for an excess of trans-SNP in two gene sets: one associated with the immune system (IMMS) and another one with behavioral system (BEHS). We identified a significant excess of trans-SNPs in IMMS (N=547), of which six of these located within genes previously associated with schizophrenia. No excess of trans-SNPs was found in BEHS, but five genes in this system harbor potential signals for balancing selection and are associated with psychiatric or neurodevelopmental disorders. Our approach evidenced recent Homo trans-SNPs that have been previously implicated in psychiatric diseases such as schizophrenia, suggesting that a genetic repertoire common to the immune and behavioral systems could have been maintained by balancing selection starting before the split between archaic and modern humans.

Errant gardeners: glial-cell-dependent synaptic pruning and neurodevelopmental disorders

The final stage of brain development is associated with the generation and maturation of neuronal synapses. However, the same period is also associated with a peak in synapse elimination - a process known as synaptic pruning - that has been proposed to be crucial for the maturation of remaining synaptic connections. Recent studies have pointed to a key role for glial cells in synaptic pruning in various parts of the nervous system and have identified a set of critical signalling pathways between glia and neurons. At the same time, brain imaging and post-mortem anatomical studies suggest that insufficient or excessive synaptic pruning may underlie several neurodevelopmental disorders, including autism, schizophrenia and epilepsy. Here, we review current data on the cellular, physiological and molecular mechanisms of glial-cell-dependent synaptic pruning and outline their potential contribution to neurodevelopmental disorders.

A molecular pathway analysis stresses the role of inflammation and oxidative stress towards cognition in schizophrenia

Cognitive processes have a genetic component and are impaired in Schizophrenia (SKZ). The exact nature of such impairment escapes definition. The aim of the present contribution was the identification of the molecular pathways enriched with mutations (SNPs) associated with cognitive performance during antipsychotic treatment. 765 individuals from the CATIE study, males = 559, mean age 40.93 ± 11.03 were included. Working memory and the verbal memory were the evaluated outcomes. A mixed regression model for repeated measures served in R for clinical and molecular pathway analysis. The analysis of quality was conducted under the following criteria: minor allele frequency >0.01, genotype call rate >95%, missing data frequency <5%, Hardy-Weimberg equilibrium threshold >0.0001. The inflation factor was controlled by lambda values. Input for the pathway analysis was SNPs at a p level <0.05 of association genome-wide. Gender, age, education and the duration of the disease were the clinical and socio-demographic variables associated with the cognitive performance. 4268977 SNPs were available after imputation and quality analysis. Pathways related to inflammation and oxidation were the most strongly associated with verbal memory and working memory at a conservative adjusted p value < 0.01. We report that inflammation and in particular the pathway associated with arachidonic acid was enriched in mutations associated with poorer performance at the verbal memory and working memory tasks in SKZ patients.

Genetics of Aggression in Alzheimer's Disease (AD)

Alzheimer’s disease (AD) is a terminal, age-related neurological syndrome exhibiting progressive cognitive and memory decline, however AD patients in addition exhibit ancillary neuropsychiatric symptoms (NPSs) and these include aggression. In this communication we provide recent evidence for the mis-regulation of a small family of genes expressed in the human hippocampus that appear to be significantly involved in expression patterns common to both AD and aggression. DNA array- and mRNA transcriptome-based gene expression analysis and candidate gene association and/or genome-wide association studies (CGAS, GWAS) of aggressive attributes in humans have revealed a surprisingly small subset of six brain genes that are also strongly associated with altered gene expression patterns in AD. These genes encoded on five different chromosomes (chr) include the androgen receptor (AR; chrXq12), brain-derived neurotrophic factor (BDNF; chr11p14.1), catechol-O-methyl transferase (COMT; chr22q11.21), neuronal specific nitric oxide synthase (NOS1; chr12q24.22), dopamine beta-hydroxylase (DBH chr9q34.2) and tryptophan hydroxylase (TPH1, chr11p15.1 and TPH2, chr12q21.1). Interestingly, (i) the expression of three of these six genes (COMT, DBH, NOS1) are highly variable; (ii) three of these six genes (COMT, DBH, TPH1) are involved in DA or serotonin metabolism, biosynthesis and/or neurotransmission; and (iii) five of these six genes (AR, BDNF, COMT, DBH, NOS1) have been implicated in the development, onset and/or propagation of schizophrenia. The magnitude of the expression of genes implicated in aggressive behavior appears to be more pronounced in the later stages of AD when compared to MCI. These recent genetic data further indicate that the extent of cognitive impairment may have some bearing on the degree of aggression which accompanies the AD phenotype.

Using Induced Pluripotent Stem Cells to Investigate Complex Genetic Psychiatric Disorders

PURPOSE OF REVIEW

Induced pluripotent stem cells (iPSCs) can be generated from human patient tissue samples, differentiated into any somatic cell type, and studied under controlled culture conditions. We review how iPSCs are used to investigate genetic factors and biological mechanisms underlying psychiatric disorders, and considerations for synthesizing data across studies.

RECENT FINDINGS

Results from patient specific-iPSC studies often reveal cellular phenotypes consistent with postmortem and brain imaging studies. Unpredicted findings illustrate the power of iPSCs as a discovery tool, but may also be attributable to limitations in modeling dynamic neural networks or difficulty in identifying the most affected neural subtype or developmental stage.

SUMMARY

Technological advances in differentiation protocols and organoid generation will enhance our ability to model the salient pathology underlying psychiatric disorders using iPSCs. The field will also benefit from context-driven interpretations of iPSC studies that recognize all potential sources of variability, including differences in patient symptomatology, genetic risk factors and affected cellular subtype.

Transcriptomic signatures of neuronal differentiation and their association with risk genes for autism spectrum and related neuropsychiatric disorders

Genes for autism spectrum disorders (ASDs) are also implicated in fragile X syndrome (FXS), intellectual disabilities (ID) or schizophrenia (SCZ), and converge on neuronal function and differentiation. The SH-SY5Y neuroblastoma cell line, the most widely used system to study neurodevelopment, is currently discussed for its applicability to model cortical development. We implemented an optimal neuronal differentiation protocol of this system and evaluated neurodevelopment at the transcriptomic level using the CoNTeXT framework, a machine-learning algorithm based on human post-mortem brain data estimating developmental stage and regional identity of transcriptomic signatures. Our improved model in contrast to currently used SH-SY5Y models does capture early neurodevelopmental processes with high fidelity. We applied regression modelling, dynamic time warping analysis, parallel independent component analysis and weighted gene co-expression network analysis to identify activated gene sets and networks. Finally, we tested and compared these sets for enrichment of risk genes for neuropsychiatric disorders. We confirm a significant overlap of genes implicated in ASD with FXS, ID and SCZ. However, counterintuitive to this observation, we report that risk genes affect pathways specific for each disorder during early neurodevelopment. Genes implicated in ASD, ID, FXS and SCZ were enriched among the positive regulators, but only ID-implicated genes were also negative regulators of neuronal differentiation. ASD and ID genes were involved in dendritic branching modules, but only ASD risk genes were implicated in histone modification or axonal guidance. Only ID genes were over-represented among cell cycle modules. We conclude that the underlying signatures are disorder-specific and that the shared genetic architecture results in overlaps across disorders such as ID in ASD. Thus, adding developmental network context to genetic analyses will aid differentiating the pathophysiology of neuropsychiatric disorders.

The role of experience in adolescent cognitive development: Integration of executive, memory, and mesolimbic systems

Adolescence marks a time of unique neurocognitive development, in which executive functions reach adult levels of maturation. While many core facets of executive function may reach maturation in childhood, these processes continue to be refined and stabilized during adolescence. We propose that this is mediated, in part, by interactions between the hippocampus and prefrontal cortex. Specifically, we propose that development of this circuit refines adolescents' ability to extract relevant information from prior experience to support task-relevant behavior. In support of this model, we review evidence for protracted structural and functional development both within and across the hippocampus and prefrontal cortex. We describe emerging research demonstrating the refinement of adolescents' ability to integrate prior experiences to support goal-oriented behavior, which parallel hippocampal-prefrontal integration. Finally, we speculate that the development of this circuit is mediated by increases in dopaminergic neuromodulation present in adolescence, which may underlie memory processing, plasticity, and circuit integration. This model provides a novel characterization of how memory and executive systems integrate throughout adolescence to support adaptive behavior.

A fly's view of neuronal remodeling

Developmental neuronal remodeling is a crucial step in sculpting the final and mature brain connectivity in both vertebrates and invertebrates. Remodeling includes degenerative events, such as neurite pruning, that may be followed by regeneration to form novel connections during normal development. Drosophila provides an excellent model to study both steps of remodeling since its nervous system undergoes massive and stereotypic remodeling during metamorphosis. Although pruning has been widely studied, our knowledge of the molecular and cellular mechanisms is far from complete. Our understanding of the processes underlying regrowth is even more fragmentary. In this review, we discuss recent progress by focusing on three groups of neurons that undergo stereotypic pruning and regrowth during metamorphosis, the mushroom body γ neurons, the dendritic arborization neurons and the crustacean cardioactive peptide peptidergic neurons. By comparing and contrasting the mechanisms involved in remodeling of these three neuronal types, we highlight the common themes and differences as well as raise key questions for future investigation in the field. WIREs Dev Biol 2016, 5:618–635. doi: 10.1002/wdev.241

For further resources related to this article, please visit the WIREs website

Nitric Oxide as a Switching Mechanism between Axon Degeneration and Regrowth during Developmental Remodeling

During development, neurons switch among growth states, such as initial axon outgrowth, axon pruning, and regrowth. By studying the stereotypic remodeling of the Drosophila mushroom body (MB), we found that the heme-binding nuclear receptor E75 is dispensable for initial axon outgrowth of MB γ neurons but is required for their developmental regrowth. Genetic experiments and pharmacological manipulations on ex-vivo-cultured brains indicate that neuronally generated nitric oxide (NO) promotes pruning but inhibits regrowth. We found that high NO levels inhibit the physical interaction between the E75 and UNF nuclear receptors, likely accounting for its repression of regrowth. Additionally, NO synthase (NOS) activity is downregulated at the onset of regrowth, at least partially, by short inhibitory NOS isoforms encoded within the NOS locus, indicating how NO production could be developmentally regulated. Taken together, these results suggest that NO signaling provides a switching mechanism between the degenerative and regenerative states of neuronal remodeling.

Epigenetic Treatment of Neuropsychiatric Disorders: Autism and Schizophrenia

Neuropsychiatric disorders are a heterogeneous group of conditions that often share underlying mitochondrial dysfunction and biological pathways implicated in their pathogenesis, progression, and treatment. To date, these disorders have proven notoriously resistant to molecular-targeted therapies, and clinical options are relegated to interventional types, which do not address the core symptoms of the disease. In this review, we discuss emerging epigenetic-driven approaches using novel acylcarnitine esters (carnitinoids) that act on master regulators of antioxidant and cytoprotective genes and mitophagic pathways. These carnitinoids are actively transported, mitochondria-localizing, biomimetic coenzyme A surrogates of short-chain fatty acids, which inhibit histone deacetylase and may reinvigorate synaptic plasticity and protect against neuronal damage. We outline these neuroprotective effects in the context of treatment of neuropsychiatric disorders such as autism spectrum disorder and schizophrenia.