Isolation of MECP2-null Rett Syndrome patient hiPS cells and isogenic controls through X-chromosome inactivation

Application of Human-Induced Pluripotent Stem Cells (hiPSCs) to Study Synaptopathy of Neurodevelopmental Disorders

Synapses are the basic structural and functional units for information processing and storage in the brain. Their diverse properties and functions ultimately underlie the complexity of human behavior. Proper development and maintenance of synapses are essential for normal functioning of the nervous system. Disruption in synaptogenesis and the consequent alteration in synaptic function have been strongly implicated to cause neurodevelopmental disorders such as autism spectrum disorders (ASDs) and schizophrenia (SCZ). The introduction of human-induced pluripotent stem cells (hiPSCs) provides a new path to elucidate disease mechanisms and potential therapies. In this review, we will discuss the advantages and limitations of using hiPSC-derived neurons to study synaptic disorders. Many mutations in genes encoding for proteins that regulate synaptogenesis have been identified in patients with ASDs and SCZ. We use Methyl-CpG binding protein 2 (MECP2), SH3 and multiple ankyrin repeat domains 3 (SHANK3) and Disrupted in schizophrenia 1 (DISC1) as examples to illustrate the promise of using hiPSCs as cellular models to elucidate the mechanisms underlying disease-related synaptopathy.

Transcriptome level analysis in Rett syndrome using human samples from different tissues

The mechanisms of neuro-genetic disorders have been mostly investigated in the brain, however, for some pathologies, transcriptomic analysis in multiple tissues represent an opportunity and a challenge to understand the consequences of the genetic mutation. This is the case for Rett Syndrome (RTT): a neurodevelopmental disorder predominantly affecting females that is characterised by a loss of purposeful movements and language accompanied by gait abnormalities and hand stereotypies. Although the genetic aetiology is largely associated to Methyl CpG binding protein 2 (MECP2) mutations, linking the pathophysiology of RTT and its clinical symptoms to direct molecular mechanisms has been difficult.One approach used to study the consequences of MECP2 dysfunction in patients, is to perform transcriptomic analysis in tissues derived from RTT patients or Induced Pluripotent Stem cells. The growing affordability and efficiency of this approach has led to a far greater understanding of the complexities of RTT syndrome but is also raised questions about previously held convictions such as the regulatory role of MECP2, the effects of different molecular mechanisms in different tissues and role of X Chromosome Inactivation in RTT.In this review we consider the results of a number of different transcriptomic analyses in different patients-derived preparations to unveil specific trends in differential gene expression across the studies. Although the analyses present limitations- such as the limited sample size- overlaps exist across these studies, and they report dysregulations in three main categories: dendritic connectivity and synapse maturation, mitochondrial dysfunction, and glial cell activity.These observations have a direct application to the disorder and give insights on the altered mechanisms in RTT, with implications on potential diagnostic criteria and treatments.

The chromatin basis of neurodevelopmental disorders: Rethinking dysfunction along the molecular and temporal axes

The complexity of the human brain emerges from a long and finely tuned developmental process orchestrated by the crosstalk between genome and environment. Vis à vis other species, the human brain displays unique functional and morphological features that result from this extensive developmental process that is, unsurprisingly, highly vulnerable to both genetically and environmentally induced alterations. One of the most striking outcomes of the recent surge of sequencing-based studies on neurodevelopmental disorders (NDDs) is the emergence of chromatin regulation as one of the two domains most affected by causative mutations or Copy Number Variations besides synaptic function, whose involvement had been largely predicted for obvious reasons. These observations place chromatin dysfunction at the top of the molecular pathways hierarchy that ushers in a sizeable proportion of NDDs and that manifest themselves through synaptic dysfunction and recurrent systemic clinical manifestation. Here we undertake a conceptual investigation of chromatin dysfunction in NDDs with the aim of systematizing the available evidence in a new framework: first, we tease out the developmental vulnerabilities in human corticogenesis as a structuring entry point into the causation of NDDs; second, we provide a much needed clarification of the multiple meanings and explanatory frameworks revolving around "epigenetics", highlighting those that are most relevant for the analysis of these disorders; finally we go in-depth into paradigmatic examples of NDD-causing chromatin dysregulation, with a special focus on human experimental models and datasets.

The promise of induced pluripotent stem cells for neurodevelopmental disorders

A major challenge in clinical genetics and medicine is represented by genetically and phenotypically highly diverse neurodevelopmental disorders, like for example intellectual disability and autism. Intellectual disability is characterized by substantial limitations in cognitive function and adaptive behaviour. At the cellular level, this is reflected by deficits in synaptic structure and plasticity and therefore has been coined as a synaptic disorder or "synaptopathy". In this review, we summarize the findings from recent studies in which iPSCs have been used to model specific neurodevelopmental syndromes, including Fragile X syndrome, Rett syndrome, Williams-Beuren syndrome and Phelan-McDermid syndrome. We discuss what we have learned from these studies and what key issues need to be addressed to move the field forward.

Use of induced pluripotent stem cells to investigate the effects of purine nucleoside phosphorylase deficiency on neuronal development

Background: Inherited defects in the function of the purine nucleoside phosphorylase (PNP) enzyme can cause severe T cell immune deficiency and early death from infection, autoimmunity, or malignancy. In addition, more than 50% of patients suffer diverse non-infectious neurological complications. However the cause for the neurological abnormalities are not known.

Objectives: Differentiate induced pluripotent stem cells (iPSC) from PNP-deficient patients into neuronal cells to better understand the effects of impaired purine metabolism on neuronal development.

Methods: Sendai virus was used to generate pluripotent stem cells from PNP-deficient and healthy control lymphoblastoid cells. Cells were differentiated into neuronal cells through the formation of embryoid bodies.

Results: After demonstration of pluripotency, normal karyotype, and retention of the PNP deficiency state, iPSC were differentiated into neuronal cells. PNP-deficient neuronal cells had reduced soma and nuclei size in comparison to cells derived from healthy controls. Spontaneous apoptosis, determined by Caspase-3 expression, was increased in PNP-deficient cells.

Conclusions: iPSC from PNP-deficient patients can be differentiated into neuronal cells, thereby providing an important tool to study the effects of impaired purine metabolism on neuronal development and potential treatments.

Statement of novelty: We report here the first generation and use of neuronal cells derived from induced pluripotent stem cells to model human PNP deficiency, thereby providing an important tool for better understanding and management of this condition.

Regulation of X-chromosome dosage compensation in human: mechanisms and model systems

The human blastocyst forms 5 days after one of the smallest human cells (the sperm) fertilizes one of the largest human cells (the egg). Depending on the sex-chromosome contribution from the sperm, the resulting embryo will either be female, with two X chromosomes (XX), or male, with an X and a Y chromosome (XY). In early development, one of the major differences between XX female and XY male embryos is the conserved process of X-chromosome inactivation (XCI), which compensates gene expression of the two female X chromosomes to match the dosage of the single X chromosome of males. Most of our understanding of the pre-XCI state and XCI establishment is based on mouse studies, but recent evidence from human pre-implantation embryo research suggests that many of the molecular steps defined in the mouse are not conserved in human. Here, we will discuss recent advances in understanding the control of X-chromosome dosage compensation in early human embryonic development and compare it to that of the mouse.This article is part of the themed issue 'X-chromosome inactivation: a tribute to Mary Lyon'.

iPSC-derived neurons profiling reveals GABAergic circuit disruption and acetylated α-tubulin defect which improves after iHDAC6 treatment in Rett syndrome

Mutations in MECP2 gene have been identified in more than 95% of patients with classic Rett syndrome, one of the most common neurodevelopmental disorders in females. Taking advantage of the breakthrough technology of genetic reprogramming, we investigated transcriptome changes in neurons differentiated from induced Pluripotent Stem Cells (iPSCs) derived from patients with different mutations. Profiling by RNA-seq in terminally differentiated neurons revealed a prominent GABAergic circuit disruption along with a perturbation of cytoskeleton dynamics. In particular, in mutated neurons we identified a significant decrease of acetylated α-tubulin which can be reverted by treatment with selective inhibitors of HDAC6, the main α-tubulin deacetylase. These findings contribute to shed light on Rett pathogenic mechanisms and provide hints for the treatment of Rett-associated epileptic behavior as well as for the definition of new therapeutic strategies for Rett syndrome.

Studying the Brain in a Dish: 3D Cell Culture Models of Human Brain Development and Disease

The study of the cellular and molecular processes of the developing human brain has been hindered by access to suitable models of living human brain tissue. Recently developed 3D cell culture models offer the promise of studying fundamental brain processes in the context of human genetic background and species-specific developmental mechanisms. Here, we review the current state of 3D human brain organoid models and consider their potential to enable investigation of complex aspects of human brain development and the underpinning of human neurological disease.

Psychiatry in a Dish: Stem Cells and Brain Organoids Modeling Autism Spectrum Disorders

Autism spectrum disorders are a group of pervasive neurodevelopmental conditions with heterogeneous etiology, characterized by deficits in social cognition, communication, and behavioral flexibility. Despite an increasing scientific effort to find the pathophysiological explanations for the disease, the neurobiological links remain unclear. A large amount of evidence suggests that pathological processes taking place in early embryonic neurodevelopment might be responsible for later manifestation of autistic symptoms. This dysfunctional development includes altered maturation/differentiation processes, disturbances in cell-cell communication, and an unbalanced ratio between certain neuronal populations. All those processes are highly dependent on the interconnectivity and three-dimensional organizations of the brain. Moreover, in order to gain a deeper understanding of the complex neurobiology of autism spectrum disorders, valid disease models are pivotal. Induced pluripotent stem cells could potentially help to elucidate the complex mechanisms of the disease and lead to the development of more effective individualized treatment. The induced pluripotent stem cells approach allows comparison between the development of various cellular phenotypes generated from cell lines of patients and healthy individuals. A newly advanced organoid technology makes it possible to create three-dimensional in vitro models of brain development and structural interconnectivity, based on induced pluripotent stem cells derived from the respective individuals. The biggest challenge for modeling psychiatric diseases in vitro is finding and establishing the link between cellular and molecular findings with the clinical symptoms, and this review aims to give an overview over the feasibility and applicability of this new tissue engineering tool in psychiatry.

Human Rett-derived neuronal progenitor cells in 3D graphene scaffold as an in vitro platform to study the effect of electrical stimulation on neuronal differentiation

Studies of electrical stimulation therapies for the treatment of neurological disorders, such as deep brain stimulation, have almost exclusively been performed using animal-models. However, because animal-models can only approximate human brain disorders, these studies should be supplemented with an in vitro human cell-culture based model to substantiate the results of animal-based studies and further investigate therapeutic benefit in humans. This study presents a novel approach to analyze the effect of electrical stimulation on the neurogenesis of patient-induced pluripotent stem cell (iPSC) derived neural progenitor cell (NPC) lines, in vitro using a 3D graphene scaffold system. The iPSC-derived hNPCs used to demonstrate the system were collected from patients with Rett syndrome, a debilitating neurodevelopmental disorder. The graphene scaffold readily supported both the wild-type and Rett NPCs. Electrical stimulation parameters were optimized to accommodate both wild-type and Rett cells. Increased cell maturation and improvements in cell morphology of the Rett cells was observed after electrical stimulation. The results of the pilot study of electrical stimulation to enhance Rett NPCs neurogenesis were promising and support further investigation of the therapy. Overall, this system provides a valuable tool to study electrical stimulation as a potential therapy for neurological disorders using patient-specific cells.

Development and disease in a dish: the epigenetics of neurodevelopmental disorders

Human neurodevelopmental disorders (NDDs) involve mutations in hundreds of individual genes, with over-representation in genes encoding proteins that alter chromatin structure to modulate gene expression. Here, we highlight efforts to model these NDDs through in vitro differentiation of patient-specific induced pluripotent stem cells into neurons. We discuss how epigenetic regulation controls normal cortical development, how mutations in several classes of epigenetic regulators contribute to NDDs, and approaches for modeling cortical development and function using both directed differentiation and formation of cerebral organoids. We explore successful applications of these models to study both syndromic and nonsyndromic NDDs and to define convergent mechanisms, addressing both the potential and challenges of using this approach to define cellular and molecular mechanisms that underlie NDDs.

X chromosome inactivation in human pluripotent stem cells as a model for human development: back to the drawing board?

BACKGROUND

Human pluripotent stem cells (hPSC), both embryonic and induced (hESC and hiPSC), are regarded as a valuable in vitro model for early human development. In order to fulfil this promise, it is important that these cells mimic as closely as possible the in vivo molecular events, both at the genetic and epigenetic level. One of the most important epigenetic events during early human development is X chromosome inactivation (XCI), the transcriptional silencing of one of the two X chromosomes in female cells. XCI is important for proper development and aberrant XCI has been linked to several pathologies. Recently, novel data obtained using high throughput single-cell technology during human preimplantation development have suggested that the XCI mechanism is substantially different from XCI in mouse. It has also been suggested that hPSC show higher complexity in XCI than the mouse. Here we compare the available recent data to understand whether XCI during human preimplantation can be properly recapitulated using hPSC.

OBJECTIVE AND RATIONALE

We will summarize what is known on the timing and mechanisms of XCI during human preimplantation development. We will compare this to the XCI patterns that are observed during hPSC derivation, culture and differentiation, and comment on the cause of the aberrant XCI patterns observed in hPSC. Finally, we will discuss the implications of the aberrant XCI patterns on the applicability of hPSC as an in vitro model for human development and as cell source for regenerative medicine.

SEARCH METHODS

Combinations of the following keywords were applied as search criteria in the PubMed database: X chromosome inactivation, preimplantation development, embryonic stem cells, induced pluripotent stem cells, primordial germ cells, differentiation.

OUTCOMES

Recent single-cell RNASeq data have shed new light on the XCI process during human preimplantation development. These indicate a gradual inactivation on both XX chromosomes, starting from Day 4 of development and followed by a random choice to inactivate one of them, instead of the mechanism in mice where imprinted XCI is followed by random XCI. We have put these new findings in perspective using previous data obtained in human (and mouse) embryos. In addition, there is an ongoing discussion whether or not hPSC lines show X chromosome reactivation upon derivation, mimicking the earliest embryonic cells, and the XCI states observed during culture of hPSC are highly variable. Recent studies have shown that hPSC rapidly progress to highly aberrant XCI patterns and that this process is probably driven by suboptimal culture conditions. Importantly, these aberrant XCI states seem to be inherited by the differentiated hPSC-progeny.

WIDER IMPLICATIONS

The aberrant XCI states (and epigenetic instability) observed in hPSC throw a shadow on their applicability as an in vitro model for development and disease modelling. Moreover, as the aberrant XCI states observed in hPSC seem to shift to a more malignant phenotype, this may also have important consequences for the safety aspect of using hPSC in the clinic.

Human-Derived Neurons and Neural Progenitor Cells in High Content Imaging Applications

Due to advances in the fields of stem cell biology and cellular engineering, a variety of commercially available human-derived neurons and neural progenitor cells (NPCs) are now available for use in research applications, including small molecule efficacy or toxicity screening. The use of human-derived neural cells is anticipated to address some of the uncertainties associated with the use of nonhuman culture models or transformed cell lines derived from human tissues. Many of the human-derived neurons and NPCs currently available from commercial sources recapitulate critical process of nervous system development including NPC proliferation, neurite outgrowth, synaptogenesis, and calcium signaling, each of which can be evaluated using high content image analysis (HCA). Human-derived neurons and NPCs are also amenable to culture in multiwell plate formats and thus may be adapted for use in HCA-based screening applications. This article reviews various types of HCA-based assays that have been used in conjunction with human-derived neurons and NPC cultures. This article also highlights instances where lower throughput analysis of neurodevelopmental processes has been performed and which demonstrate a potential for adaptation to higher-throughout imaging methods. Finally, a generic protocol for evaluating neurite outgrowth in human-derived neurons using a combination of immunocytochemistry and HCA is presented. The information provided in this article is intended to serve as a resource for cell model and assay selection for those interested in evaluating neurodevelopmental processes in human-derived cells.

Modeling Inflammation in Autism Spectrum Disorders Using Stem Cells

Recent reports show an increase in the incidence of Autism Spectrum Disorders (ASD) to 1 in every 59 children up to 8 years old in 11 states in North America. Induced pluripotent stem cell (iPSC) technology offers a groundbreaking platform for the study of polygenic neurodevelopmental disorders in live cells. Robust inflammation states and immune system dysfunctions are associated with ASD and several cell types participate on triggering and sustaining these processes. In this review, we will examine the contribution of neuroinflammation to the development of autistic features and discuss potential therapeutic approaches. We will review the available tools, emphasizing stem cell modeling as a technology to investigate the various molecular pathways and different cell types involved in the process of neuroinflammation in ASD.

Stem cell-derived neurons from autistic individuals with SHANK3 mutation show morphogenetic abnormalities during early development

Shank3 is a structural protein found predominantly at the postsynaptic density. Mutations in the SHANK3 gene have been associated with risk for autism spectrum disorder (ASD). We generated induced pluripotent stem cells (iPSCs) from control individuals and from human donors with ASD carrying microdeletions of SHANK3. In addition, we used Zinc finger nucleases to generate isogenic SHANK3 knockout human embryonic stem (ES) cell lines. We differentiated pluripotent cells into either cortical or olfactory placodal neurons. We show that patient-derived placodal neurons make fewer synapses than control cells. Moreover, patient-derived cells display a developmental phenotype: young postmitotic neurons have smaller cell bodies, more extensively branched neurites, and reduced motility compared with controls. These phenotypes were mimicked by SHANK3-edited ES cells and rescued by transduction with a Shank3 expression construct. This developmental phenotype is not observed in the same iPSC lines differentiated into cortical neurons. Therefore, we suggest that SHANK3 has a critical role in neuronal morphogenesis in placodal neurons and that early defects are associated with ASD-associated mutations.

MECP2 Is Post-transcriptionally Regulated during Human Neurodevelopment by Combinatorial Action of RNA-Binding Proteins and miRNAs

A progressive increase in MECP2 protein levels is a crucial and precisely regulated event during neurodevelopment, but the underlying mechanism is unclear. We report that MECP2 is regulated post-transcriptionally during in vitro differentiation of human embryonic stem cells (hESCs) into cortical neurons. Using reporters to identify functional RNA sequences in the MECP2 3' UTR and genetic manipulations to explore the role of interacting factors on endogenous MECP2, we discover combinatorial mechanisms that regulate RNA stability and translation. The RNA-binding protein PUM1 and pluripotent-specific microRNAs destabilize the long MECP2 3' UTR in hESCs. Hence, the 3' UTR appears to lengthen during differentiation as the long isoform becomes stable in neurons. Meanwhile, translation of MECP2 is repressed by TIA1 in hESCs until HuC predominates in neurons, resulting in a switch to translational enhancement. Ultimately, 3' UTR-directed translational fine-tuning differentially modulates MECP2 protein in the two cell types to levels appropriate for normal neurodevelopment.

Spatiotemporal Proteomic Profiling of Human Cerebral Development

Mass spectrometry (MS) analysis of human post-mortem central nervous system (CNS) tissue and induced pluripotent stem cell (iPSC)-based directed differentiations offer complementary avenues to define protein signatures of neurodevelopment. Methodological improvements of formalin-fixed, paraffin-embedded (FFPE) protein isolation now enable widespread proteomic analysis of well-annotated archival tissue samples in the context of development and disease. Here, we utilize a shotgun label-free quantification (LFQ) MS method to profile magnetically enriched human cortical neurons and neural progenitor cells (NPCs) derived from iPSCs. We use these signatures to help define spatiotemporal protein dynamics of developing human FFPE cerebral regions. We show that the use of high resolution Q Exactive mass spectrometers now allow simultaneous quantification of >2700 proteins in a single LFQ experiment and provide sufficient coverage to define novel biomarkers and signatures of NPC maintenance and differentiation. Importantly, we show that this abbreviated strategy allows efficient recovery of novel cytoplasmic, membrane-specific and synaptic proteins that are shared between both in vivo and in vitro neuronal differentiation. This study highlights the discovery potential of non-comprehensive high-throughput proteomic profiling of unfractionated clinically well-annotated FFPE human tissue from a diverse array of development and diseased states.

Human induced pluripotent stem cells for modelling neurodevelopmental disorders

We currently have a poor understanding of the pathogenesis of neurodevelopmental disorders, owing to the fact that postmortem and imaging studies can only measure the postnatal status quo and offer little insight into the processes that give rise to the observed outcomes. Human induced pluripotent stem cells (hiPSCs) should, in principle, prove powerful for elucidating the pathways that give rise to neurodevelopmental disorders. hiPSCs are embryonic-stem-cell-like cells that can be derived from somatic cells. They retain the unique genetic signature of the individual from whom they were derived, and thus enable researchers to recapitulate that individual's idiosyncratic neural development in a dish. In the case of individuals with disease, we can re-enact the disease-altered trajectory of brain development and examine how and why phenotypic and molecular abnormalities arise in these diseased brains. Here, we review hiPSC biology and possible experimental designs when using hiPSCs to model disease. We then discuss existing hiPSC models of neurodevelopmental disorders. Our hope is that, as some studies have already shown, hiPSCs will illuminate the pathophysiology of developmental disorders of the CNS and lead to therapeutic options for the millions that are affected by these conditions.

Induction of Pluripotent Stem Cells from a Manifesting Carrier of Duchenne Muscular Dystrophy and Characterization of Their X-Inactivation Status

Three to eight percent of female carriers of Duchenne muscular dystrophy (DMD) develop dystrophic symptoms ranging from mild muscle weakness to a rapidly progressive DMD-like muscular dystrophy due to skewed inactivation of X chromosomes during early development. Here, we generated human induced pluripotent stem cells (hiPSCs) from a manifesting female carrier using retroviral or Sendai viral (SeV) vectors and determined their X-inactivation status. Although manifesting carrier-derived iPS cells showed normal expression of human embryonic stem cell markers and formed well-differentiated teratomas in vivo, many hiPS clones showed bi-allelic expression of the androgen receptor (AR) gene and loss of X-inactivation-specific transcript and trimethyl-histone H3 (Lys27) signals on X chromosomes, suggesting that both X chromosomes of the hiPS cells are in an active state. Importantly, normal dystrophin was expressed in multinucleated myotubes differentiated from a manifesting carrier of DMD-hiPS cells with XaXa pattern. AR transcripts were also equally transcribed from both alleles in induced myotubes. Our results indicated that the inactivated X chromosome in the patient's fibroblasts was activated during reprogramming, and XCI occurred randomly during differentiation.

Usage of Human Mesenchymal Stem Cells in Cell-based Therapy: Advantages and Disadvantages

The use of human mesenchymal stem cells (hMSCs) in cell-based therapy has attracted extensive interest in the field of regenerative medicine, and it shows applications to numerous incurable diseases. hMSCs show several superior properties for therapeutic use compared to other types of stem cells. Different cell types are discussed in terms of their advantages and disadvantages, with focus on the characteristics of hMSCs. hMSCs can proliferate readily and produce differentiated cells that can substitute for the targeted affected tissue. To maximize the therapeutic effects of hMSCs, a substantial number of these cells are essential, requiring extensive ex vivo cell expansion. However, hMSCs have a limited lifespan in an in vitro culture condition. The senescence of hMSCs is a double-edged sword from the viewpoint of clinical applications. Although their limited cell proliferation potency protects them from malignant transformation after transplantation, senescence can alter various cell functions including proliferation, differentiation, and migration, that are essential for their therapeutic efficacy. Numerous trials to overcome the limited lifespan of mesenchymal stem cells are discussed.

The State of Skewed X Chromosome Inactivation is Retained in the Induced Pluripotent Stem Cells from a Female with Hemophilia B

Skewed X chromosome inactivation (XCI) is a rare reason for hemophilia B in females. It is indefinite whether X chromosome reactivation (XCR) would occur when cells of hemophilia B patients with skewed XCI were reprogrammed into induced pluripotent stem cells (iPSCs). In this study, we investigated a female hemophilia B patient with a known F9 gene mutation: c.676C>T, p.Arg226Trp. We demonstrated that skewed XCI was the pathogenesis of the patient, and we successfully generated numerous iPSC colonies of the patient from peripheral blood mononuclear cells (PBMNCs), which was the first time for generating hemophilia-specific iPSCs from PBMNCs. Then we detected the XCI state of these iPSCs. Ninety-two iPSC lines were picked for XCI analysis. All of them retained an inactive X chromosome, which could be proved by amplification of the androgen receptor gene and XIST (X inactivation-specific transcript), expression of H3K27me3, and existence of XIST clouds in XIST RNA fluorescence in situ hybridization (FISH) analysis. We attempted to obtain iPSC lines with the wild-type F9 gene on the active X chromosome for further disease treatment. But it turned out that the patient's iPSCs were still skewed such as the somatic cells with 92 iPSC lines having mutant F9 on the active X chromosome. In conclusion, skewed XCI is one reason for hemophilia in females. PBMNCs are excellent somatic cell resources for hemophilia patients to do reprogramming. More attentions should be paid to generate naive iPSCs with two active X chromosomes for further clinical disease treatment. The state of skewed XCI is retained in the iPSCs from a female with hemophilia B.

CREB Signaling Is Involved in Rett Syndrome Pathogenesis

Rett syndrome (RTT) is a debilitating neurodevelopmental disorder caused by mutations in the MECP2 gene. To facilitate the study of cellular mechanisms in human cells, we established several human stem cell lines: human embryonic stem cell (hESC) line carrying the common T158M mutation (MECP2^T158M/T158M ), hESC line expressing no MECP2 (MECP2-KO), congenic pair of wild-type and mutant RTT patient-specific induced pluripotent stem cell (iPSC) line carrying the V247fs mutation (V247fs-WT and V247fs-MT), and iPSC line in which the V247fs mutation was corrected by CRISPR/Cas9-based genome editing (V247fs-MT-correction). Detailed analyses of forebrain neurons differentiated from these human stem cell lines revealed genotype-dependent quantitative phenotypes in neurite growth, dendritic complexity, and mitochondrial function. At the molecular level, we found a significant reduction in the level of CREB and phosphorylated CREB in forebrain neurons differentiated from MECP2^T158M/T158M , MECP2-KO, and V247fs-MT stem cell lines. Importantly, overexpression of CREB or pharmacological activation of CREB signaling in those forebrain neurons rescued the phenotypes in neurite growth, dendritic complexity, and mitochondrial function. Finally, pharmacological activation of CREB in the female Mecp2 heterozygous mice rescued several behavioral defects. Together, our study establishes a robust in vitro platform for consistent quantitative evaluation of genotype-dependent RTT phenotypes, reveals a previously unappreciated role of CREB signaling in RTT pathogenesis, and identifies a potential therapeutic target for RTT.SIGNIFICANCE STATEMENT Our study establishes a robust human stem cell-based platform for consistent quantitative evaluation of genotype-dependent Rett syndrome (RTT) phenotypes at the cellular level. By providing the first evidence that enhancing cAMP response element binding protein signaling can alleviate RTT phenotypes both in vitro and in vivo, we reveal a previously unappreciated role of cAMP response element binding protein signaling in RTT pathogenesis, and identify a potential therapeutic target for RTT.

Modeling neurodevelopmental and psychiatric diseases with human iPSCs

Neurodevelopmental and psychiatric disorders, including autism spectrum disorder and schizophrenia, are complex and heterogeneous disorders that affect a large portion of the world's population. While the causes are still poorly understood, currently available treatments are limited; the development of rational therapeutics based on an understanding of the etiology and pathogenesis of the disease is imperative. The breakthrough technology of deriving induced pluripotent stem cells (iPSCs), reprogrammed from somatic cells of healthy subjects or patients, offers an unprecedented opportunity to recapitulate both normal and pathological development of human tissue, thereby opening up a new avenue for disease modeling and drug development in a more genetically tractable and disease-relevant system. Here, I review the recent progress in the use of human iPSCs for modeling neurodevelopmental and psychiatric disorders and developing novel therapeutic strategies, and discuss challenges in this rapidly moving field. © 2017 Wiley Periodicals, Inc.

Modeling autism spectrum disorders with human neurons

Autism spectrum disorder (ASD) is a group of neurodevelopmental disorders characterized by impaired social communication and interactions and by restricted and repetitive behaviors. Although ASD is suspected to have a heritable or sporadic genetic basis, its underlying etiology and pathogenesis are not well understood. Therefore, viable human neurons and glial cells produced using induced pluripotent stem cells (iPSC) to reprogram cells from individuals affected with ASD provide an unprecedented opportunity to elucidate the pathophysiology of these disorders, providing novel insights regarding ASD and a potential platform to develop and test therapeutic compounds. Herein, we discuss the state of art with regards to ASD modeling, including limitations of this technology, as well as potential future directions. This article is part of a Special Issue entitled SI: Exploiting human neurons.

Differential X Chromosome Inactivation Patterns during the Propagation of Human Induced Pluripotent Stem Cells

Human induced pluripotent stem cells (hiPSCs) represent a potentially useful tool for studying the molecular mechanisms of disease thanks to their ability to generate patient-specific hiPSC clones. However, previous studies have reported that DNA methylation profiles, including those for imprinted genes, may change during passaging of hiPSCs. This is particularly problematic for hiPSC models of X-linked disease, because unstable X chromosome inactivation status may affect the detection of phenotypes. In the present study, we examined the epigenetic status of hiPSCs derived from patients with Rett syndrome, an X-linked disease, during long-term culture. To analyze X chromosome inactivation, we used a methylation-specific polymerase chain reaction (MSP) to assay the human androgen receptor locus (HUMARA). We found that single cell-derived hiPSC clones exhibit various states of X chromosome inactivation immediately after clonal isolation, even when established simultaneously from a single donor. X chromosome inactivation states remain variable in hiPSC clones at early passages, and this variability may affect cellular phenotypes characteristic of X-linked diseases. Careful evaluation of X chromosome inactivation in hiPSC clones, particularly in early passages, by methods such as HUMARA-MSP, is therefore important when using patient-specific hiPSCs to model X-linked disease.

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.

A review of Rett syndrome (RTT) with induced pluripotent stem cells

Human induced pluripotent stem cells (hiPSCs) are pluripotent stem cells generated from somatic cells by the introduction of a combination of pluripotency-associated genes such as OCT4, SOX2, along with either KLF4 and c-MYC or NANOG and LIN28 via retroviral or lentiviral vectors. Most importantly, hiPSCs are similar to human embryonic stem cells (hESCs) functionally as they are pluripotent and can potentially differentiate into any desired cell type when provided with the appropriate cues, but do not have the ethical issues surrounding hESCs. For these reasons, hiPSCs have huge potential in translational medicine such as disease modeling, drug screening, and cellular therapy. Indeed, patient-specific hiPSCs have been generated for a multitude of diseases, including many with a neurological basis, in which disease phenotypes have been recapitulated in vitro and proof-of-principle drug screening has been performed. As the techniques for generating hiPSCs are refined and these cells become a more widely used tool for understanding brain development, the insights they produce must be understood in the context of the greater complexity of the human genome and the human brain. Disease models using iPS from Rett syndrome (RTT) patient's fibroblasts have opened up a new avenue of drug discovery for therapeutic treatment of RTT. The analysis of X chromosome inactivation (XCI) upon differentiation of RTT-hiPSCs into neurons will be critical to conclusively demonstrate the isolation of pre-XCI RTT-hiPSCs in comparison to post-XCI RTT-hiPSCs. The current review projects on iPSC studies in RTT as well as XCI in hiPSC were it suggests for screening new potential therapeutic targets for RTT in future for the benefit of RTT patients. In conclusion, patient-specific drug screening might be feasible and would be particularly helpful in disorders where patients frequently have to try multiple drugs before finding a regimen that works.

Utility of Induced Pluripotent Stem Cells for the Study and Treatment of Genetic Diseases: Focus on Childhood Neurological Disorders

The study of neurological disorders often presents with significant challenges due to the inaccessibility of human neuronal cells for further investigation. Advances in cellular reprogramming techniques, have however provided a new source of human cells for laboratory-based research. Patient-derived induced pluripotent stem cells (iPSCs) can now be robustly differentiated into specific neural subtypes, including dopaminergic, inhibitory GABAergic, motorneurons and cortical neurons. These neurons can then be utilized for in vitro studies to elucidate molecular causes underpinning neurological disease. Although human iPSC-derived neuronal models are increasingly regarded as a useful tool in cell biology, there are a number of limitations, including the relatively early, fetal stage of differentiated cells and the mainly two dimensional, simple nature of the in vitro system. Furthermore, clonal variation is a well-described phenomenon in iPSC lines. In order to account for this, robust baseline data from multiple control lines is necessary to determine whether a particular gene defect leads to a specific cellular phenotype. Over the last few years patient-derived neural cells have proven very useful in addressing several mechanistic questions related to central nervous system diseases, including early-onset neurological disorders of childhood. Many studies report the clinical utility of human-derived neural cells for testing known drugs with repurposing potential, novel compounds and gene therapies, which then can be translated to clinical reality. iPSCs derived neural cells, therefore provide great promise and potential to gain insight into, and treat early-onset neurological disorders.

Modeling psychiatric disorders: from genomic findings to cellular phenotypes

Major programs in psychiatric genetics have identified >150 risk loci for psychiatric disorders. These loci converge on a small number of functional pathways, which span conventional diagnostic criteria, suggesting a partly common biology underlying schizophrenia, autism and other psychiatric disorders. Nevertheless, the cellular phenotypes that capture the fundamental features of psychiatric disorders have not yet been determined. Recent advances in genetics and stem cell biology offer new prospects for cell-based modeling of psychiatric disorders. The advent of cell reprogramming and induced pluripotent stem cells (iPSC) provides an opportunity to translate genetic findings into patient-specific in vitro models. iPSC technology is less than a decade old but holds great promise for bridging the gaps between patients, genetics and biology. Despite many obvious advantages, iPSC studies still present multiple challenges. In this expert review, we critically review the challenges for modeling of psychiatric disorders, potential solutions and how iPSC technology can be used to develop an analytical framework for the evaluation and therapeutic manipulation of fundamental disease processes.

Histone deacetylase 3 associates with MeCP2 to regulate FOXO and social behavior

Mutations in MECP2 cause the neurodevelopmental disorder Rett syndrome (RTT). The RTT missense MECP2^R306C mutation prevents MeCP2 interaction with NCoR/Histone deacetylase 3 (HDAC3); however, the neuronal function of HDAC3 is incompletely understood. We report that neuronal deletion of Hdac3 in mice elicits abnormal locomotor coordination, sociability, and cognition. Transcriptional and chromatin profiling revealed HDAC3 positively regulates a subset of genes and is recruited to active gene promoters via MeCP2. HDAC3-associated promoters are enriched for the FOXO transcription factors, and FOXO acetylation is elevated in Hdac3 KO and Mecp2 KO neurons. Human RTT patient-derived MECP2^R306C neural progenitor cells have deficits in HDAC3 and FOXO recruitment and gene expression. Gene editing of MECP2^R306C cells to generate isogenic controls rescued HDAC3-FOXO-mediated impairments in gene expression. Our data suggests that HDAC3 interaction with MeCP2 positively regulates a subset of neuronal genes through FOXO deacetylation, and disruption of HDAC3 contributes to cognitive and social impairment.

Idiopathic Autism: Cellular and Molecular Phenotypes in Pluripotent Stem Cell-Derived Neurons

Autism spectrum disorder is a complex neurodevelopmental disorder whose pathophysiology remains elusive as a consequence of the unavailability for study of patient brain neurons; this deficit may potentially be circumvented by neural differentiation of induced pluripotent stem cells. Rare syndromes with single gene mutations and autistic symptoms have significantly advanced the molecular and cellular understanding of autism spectrum disorders; however, in aggregate, they only represent a fraction of all cases of autism. In an effort to define the cellular and molecular phenotypes in human neurons of non-syndromic autism, we generated induced pluripotent stem cells (iPSCs) from three male autism spectrum disorder patients who had no identifiable clinical syndromes, and their unaffected male siblings and subsequently differentiated these patient-specific stem cells into electrophysiologically active neurons. iPSC-derived neurons from these autistic patients displayed decreases in the frequency and kinetics of spontaneous excitatory postsynaptic currents relative to controls, as well as significant decreases in Na⁺ and inactivating K⁺ voltage-gated currents. Moreover, whole-genome microarray analysis of gene expression identified 161 unique genes that were significantly differentially expressed in autistic patient iPSC-derived neurons (>twofold, FDR < 0.05). These genes were significantly enriched for processes related to synaptic transmission, such as neuroactive ligand-receptor signaling and extracellular matrix interactions, and were enriched for genes previously associated with autism spectrum disorder. Our data demonstrate aberrant voltage-gated currents and underlying molecular changes related to synaptic function in iPSC-derived neurons from individuals with idiopathic autism as compared to unaffected siblings controls.

Using Patient-Derived Induced Pluripotent Stem Cells to Model and Treat Epilepsies

Human induced pluripotent stem cells (iPSCs) are transforming the fields of disease modeling and precision therapy. For the treatment of neurological disorders, iPSCs introduce the possibility for targeted cell-based therapies by deriving patient-specific neural tissue in vitro that may ultimately be used for transplantation. We review iPSC technologies and their applications that have already advanced our understanding of neurological disorders, focusing on the epilepsies. We also discuss the application of powerful new tools such as genome editing and multi-well, multi-electrode array recording platforms to iPSC disease modeling and therapy development for the epilepsies. Despite some limitations, the field of iPSCs is evolving rapidly and is quickly becoming vital for understanding mechanisms of genetic epilepsies and for future patient-specific therapeutic applications.

Modeling the autistic cell: iPSCs recapitulate developmental principles of syndromic and nonsyndromic ASD

The opportunity to model autism spectrum disorders (ASD) through generation of patient-derived induced pluripotent stem cells (iPSCs) is currently an emerging topic. Wide-scale research of altered brain circuits in syndromic ASD, including Rett Syndrome, Fragile X Syndrome, Angelman's Syndrome and sporadic Schizophrenia, was made possible through animal models. However, possibly due to species differences, and to the possible contribution of epigenetics in the pathophysiology of these diseases, animal models fail to recapitulate many aspects of ASD. With the advent of iPSCs technology, 3D cultures of patient-derived cells are being used to study complex neuronal phenotypes, including both syndromic and nonsyndromic ASD. Here, we review recent advances in using iPSCs to study various aspects of the ASD neuropathology, with emphasis on the efforts to create in vitro model systems for syndromic and nonsyndromic ASD. We summarize the main cellular activity phenotypes and aberrant genetic interaction networks that were found in iPSC-derived neurons of syndromic and nonsyndromic autistic patients.

The Human Model: Changing Focus on Autism Research

The lack of live human brain cells for research has slowed progress toward understanding the mechanisms underlying autism spectrum disorders. A human model using reprogrammed patient somatic cells offers an attractive alternative, as it captures a patient's genome in relevant cell types. Despite the current limitations, the disease-in-a-dish approach allows for progressive time course analyses of target cells, offering a unique opportunity to investigate the cellular and molecular alterations before symptomatic onset. Understanding the current drawbacks of this model is essential for the correct data interpretation and extrapolation of conclusions applicable to the human brain. Innovative strategies for collecting biological material and clinical information from large patient cohorts are important for increasing the statistical power that will allow for the extraction of information from the noise resulting from the variability introduced by reprogramming and differentiation methods. Working with large patient cohorts is also important for understanding how brain cells derived from diverse human genetic backgrounds respond to specific drugs, creating the possibility of personalized medicine for autism spectrum disorders.

Single-Cell XIST Expression in Human Preimplantation Embryos and Newly Reprogrammed Female Induced Pluripotent Stem Cells

The process of X chromosome inactivation (XCI) during reprogramming to produce human induced pluripotent stem cells (iPSCs), as well as during the extensive programming that occurs in human preimplantation development, is not well‐understood. Indeed, studies of XCI during reprogramming to iPSCs report cells with two active X chromosomes and/or cells with one inactive X chromosome. Here, we examine expression of the long noncoding RNA, XIST, in single cells of human embryos through the oocyte‐to‐embryo transition and in new mRNA reprogrammed iPSCs. We show that XIST is first expressed beginning at the 4‐cell stage, coincident with the onset of embryonic genome activation in an asynchronous manner. Additionally, we report that mRNA reprogramming produces iPSCs that initially express XIST transcript; however, expression is rapidly lost with culture. Loss of XIST and H3K27me3 enrichment at the inactive X chromosome at late passage results in X chromosome expression changes. Our data may contribute to applications in disease modeling and potential translational applications of female stem cells. Stem Cells2015;33:1771–1781

Concise Review: Progress and Challenges in Using Human Stem Cells for Biological and Therapeutics Discovery: Neuropsychiatric Disorders

In facing the daunting challenge of using human embryonic and induced pluripotent stem cells to study complex neural circuit disorders such as schizophrenia, mood and anxiety disorders, and autism spectrum disorders, a 2012 National Institute of Mental Health workshop produced a set of recommendations to advance basic research and engage industry in cell-based studies of neuropsychiatric disorders. This review describes progress in meeting these recommendations, including the development of novel tools, strides in recapitulating relevant cell and tissue types, insights into the genetic basis of these disorders that permit integration of risk-associated gene regulatory networks with cell/circuit phenotypes, and promising findings of patient-control differences using cell-based assays. However, numerous challenges are still being addressed, requiring further technological development, approaches to resolve disease heterogeneity, and collaborative structures for investigators of different disciplines. Additionally, since data obtained so far is on small sample sizes, replication in larger sample sets is needed. A number of individual success stories point to a path forward in developing assays to translate discovery science to therapeutics development.

Modeling psychiatric disorders with patient-derived iPSCs

Psychiatric disorders are heterogeneous disorders characterized by complex genetics, variable symptomatology, and anatomically distributed pathology, all of which present challenges for effective treatment. Current treatments are often blunt tools used to ameliorate the most severe symptoms, often at the risk of disrupting functional neural systems, thus there is a pressing need to develop rational therapeutics. Induced pluripotent stem cells (iPSCs) reprogrammed from patient somatic cells offer an unprecedented opportunity to recapitulate both normal and pathologic human tissue and organ development, and provides new approaches for understanding disease mechanisms and for drug discovery with higher predictability of their effects in humans. Here we review recent progress and challenges in using human iPSCs for modeling neuropsychiatric disorders and developing novel therapeutic strategies.

Advancing drug discovery for neuropsychiatric disorders using patient-specific stem cell models

Compelling clinical, social, and economic reasons exist to innovate in the process of drug discovery for neuropsychiatric disorders. The use of patient-specific, induced pluripotent stem cells (iPSCs) now affords the ability to generate neuronal cell-based models that recapitulate key aspects of human disease. In the context of neuropsychiatric disorders, where access to physiologically active and relevant cell types of the central nervous system for research is extremely limiting, iPSC-derived in vitro culture of human neurons and glial cells is transformative. Potential applications relevant to early stage drug discovery, include support of quantitative biochemistry, functional genomics, proteomics, and perhaps most notably, high-throughput and high-content chemical screening. While many phenotypes in human iPSC-derived culture systems may prove adaptable to screening formats, addressing the question of which in vitro phenotypes are ultimately relevant to disease pathophysiology and therefore more likely to yield effective pharmacological agents that are disease-modifying treatments requires careful consideration. Here, we review recent examples of studies of neuropsychiatric disorders using human stem cell models where cellular phenotypes linked to disease and functional assays have been reported. We also highlight technical advances using genome-editing technologies in iPSCs to support drug discovery efforts, including the interpretation of the functional significance of rare genetic variants of unknown significance and for the purpose of creating cell type- and pathway-selective functional reporter assays. Additionally, we evaluate the potential of in vitro stem cell models to investigate early events of disease pathogenesis, in an effort to understand the underlying molecular mechanism, including the basis of selective cell-type vulnerability, and the potential to create new cell-based diagnostics to aid in the classification of patients and subsequent selection for clinical trials. A number of key challenges remain, including the scaling of iPSC models to larger cohorts and integration with rich clinicopathological information and translation of phenotypes. Still, the overall use of iPSC-based human cell models with functional cellular and biochemical assays holds promise for supporting the discovery of next-generation neuropharmacological agents for the treatment and ultimately prevention of a range of severe mental illnesses.

Functional Evaluations of Genes Disrupted in Patients with Tourette's Disorder

Tourette's disorder (TD) is a highly heritable neurodevelopmental disorder with complex genetic architecture and unclear neuropathology. Disruptions of particular genes have been identified in subsets of TD patients. However, none of the findings have been replicated, probably due to the complex and heterogeneous genetic architecture of TD that involves both common and rare variants. To understand the etiology of TD, functional analyses are required to characterize the molecular and cellular consequences caused by mutations in candidate genes. Such molecular and cellular alterations may converge into common biological pathways underlying the heterogeneous genetic etiology of TD patients. Herein, we review specific genes implicated in TD etiology, discuss the functions of these genes in the mammalian central nervous system and the corresponding behavioral anomalies exhibited in animal models, and importantly, review functional analyses that can be performed to evaluate the role(s) that the genetic disruptions might play in TD. Specifically, the functional assays include novel cell culture systems, genome editing techniques, bioinformatics approaches, transcriptomic analyses, and genetically modified animal models applied or developed to study genes associated with TD or with other neurodevelopmental and neuropsychiatric disorders. By describing methods used to study diseases with genetic architecture similar to TD, we hope to develop a systematic framework for investigating the etiology of TD and related disorders.

Concise Review: Exciting Cells: Modeling Genetic Epilepsies with Patient-Derived Induced Pluripotent Stem Cells

Human induced pluripotent stem cell (iPSC) models of epilepsy are becoming a revolutionary platform for mechanistic studies and drug discovery. The skyrocketing pace of epilepsy gene discovery is vastly outstripping the development of in vivo animal models. Currently, antiepileptic drug prescribing to patients with specific genetic epilepsies is based on small-scale clinical trials and empiricism; however, rapid production of patient-derived iPSC models will allow for precision therapy. We review iPSC-based studies that have already afforded novel discoveries in diseases with epileptic phenotypes, as well as challenges to using iPSC-based neurological disease models. We also discuss iPSC-derived cardiomyocyte studies of arrhythmia-inducing ion channelopathies that exemplify novel drug discovery and use of multielectrode array technology that can be translated to epilepsy research. Beyond initial studies of Rett, Timothy, Phelan-McDermid, and Dravet syndromes, the stage is set for groundbreaking iPSC-based mechanistic and therapeutic discoveries in genetic epilepsies with the potential to impact patient treatment and quality of life.

A Dishful of a Troubled Mind: Induced Pluripotent Stem Cells in Psychiatric Research

Neuronal differentiation of induced pluripotent stem cells and direct reprogramming represent powerful methods for modeling the development of neurons in vitro. Moreover, this approach is also a means for comparing various cellular phenotypes between cell lines originating from healthy and diseased individuals or isogenic cell lines engineered to differ at only one or a few genomic loci. Despite methodological constraints and initial skepticism regarding this approach, the field is expanding at a fast pace. The improvements include the development of new differentiation protocols resulting in selected neuronal populations (e.g., dopaminergic, GABAergic, hippocampal, and cortical), the widespread use of genome editing methods, and single-cell techniques. A major challenge awaiting in vitro disease modeling is the integration of clinical data in the models, by selection of well characterized clinical populations. Ideally, these models will also demonstrate how different diagnostic categories share overlapping molecular disease mechanisms, but also have unique characteristics. In this review we evaluate studies with regard to the described developments, to demonstrate how differentiation of induced pluripotent stem cells and direct reprogramming can contribute to psychiatry.

Induced pluripotent stem cells for modeling neurological disorders

Several diseases have been successfully modeled since the development of induced pluripotent stem cell (iPSC) technology in 2006. Since then, methods for increased reprogramming efficiency and cell culture maintenance have been optimized and many protocols for differentiating stem cell lines have been successfully developed, allowing the generation of several cellular subtypes in vitro. Gene editing technologies have also greatly advanced lately, enhancing disease-specific phenotypes by creating isogenic cell lines, allowing mutations to be corrected in affected samples or inserted in control lines. Neurological disorders have benefited the most from iPSC-disease modeling for its capability for generating disease-relevant cell types in vitro from the central nervous system, such as neurons and glial cells, otherwise only available from post-mortem samples. Patient-specific iPSC-derived neural cells can recapitulate the phenotypes of these diseases and therefore, considerably enrich our understanding of pathogenesis, disease mechanism and facilitate the development of drug screening platforms for novel therapeutic targets. Here, we review the accomplishments and the current progress in human neurological disorders by using iPSC modeling for Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, spinal muscular atrophy, amyotrophic lateral sclerosis, duchenne muscular dystrophy, schizophrenia and autism spectrum disorders, which include Timothy syndrome, Fragile X syndrome, Angelman syndrome, Prader-Willi syndrome, Phelan-McDermid, Rett syndrome as well as Nonsyndromic Autism.

Pluripotent Stem Cells: Current Understanding and Future Directions

Pluripotent stem cells have the ability to undergo self-renewal and to give rise to all cells of the tissues of the body. However, this definition has been recently complicated by the existence of distinct cellular states that display these features. Here, we provide a detailed overview of the family of pluripotent cell lines derived from early mouse and human embryos and compare them with induced pluripotent stem cells. Shared and distinct features of these cells are reported as additional hallmark of pluripotency, offering a comprehensive scenario of pluripotent stem cells.

Applications of CRISPR-Cas systems in neuroscience

Genome-editing tools, and in particular those based on CRISPR-Cas (clustered regularly interspaced short palindromic repeat (CRISPR)-CRISPR-associated protein) systems, are accelerating the pace of biological research and enabling targeted genetic interrogation in almost any organism and cell type. These tools have opened the door to the development of new model systems for studying the complexity of the nervous system, including animal models and stem cell-derived in vitro models. Precise and efficient gene editing using CRISPR-Cas systems has the potential to advance both basic and translational neuroscience research.

Modeling synaptogenesis in schizophrenia and autism using human iPSC derived neurons

Schizophrenia (SCZ) and autism spectrum disorder (ASD) are genetically and phenotypically complex disorders of neural development. Human genetic studies, as well as studies examining structural changes at the cellular level, have converged on glutamatergic synapse formation, function, and maintenance as common pathophysiologic substrates involved in both disorders. Synapses as basic functional units of the brain are continuously modified by experience throughout life, therefore they are particularly attractive candidates for targeted therapy. Until recently we lacked a system to evaluate dynamic changes that lead to synaptic abnormalities. With the development of techniques to generate induced pluripotent stem cells (iPSCs) from patients, we are now able to study neuronal and synaptic development in cells from individual patients in the context of genetic changes conferring disease susceptibility. In this review, we discuss recent studies focusing on neural cells differentiated from SCZ and ASD patient iPSCs. These studies support a central role for glutamatergic synapse formation and function in both disorders and demonstrate that iPSC derived neurons offer a potential system for further evaluation of processes leading to synaptic dysregulation and for the design and screening of future therapies.

Transcriptomics analysis of iPSC-derived neurons and modeling of neuropsychiatric disorders

Induced pluripotent stem cell (iPSC)-derived neurons and neural progenitors are great resources for studying neural development and differentiation and their disruptions in disease conditions, and hold the promise of future cell therapy. In general, iPSC lines can be established either specifically from patients with neuropsychiatric disorders or from healthy subjects. The iPSCs can then be induced to differentiate into neural lineages and the iPSC-derived neurons are valuable for various types of cell-based assays that seek to understand disease mechanisms and identify and test novel therapies. In addition, it is an ideal system for gene expression profiling (i.e., transcriptomic analysis), an efficient and cost-effective way to explore the genetic programs regulating neurodevelopment. Moreover, transcriptomic comparison, which can be performed between patient-derived samples and controls, or in control lines in which the expression of specific genes has been disrupted, can uncover convergent gene targets and pathways that are downstream of the hundreds of candidate genes that have been associated with neuropsychiatric disorders. The results, especially after integration with spatiotemporal transcriptomic profiles of normal human brain development, have indeed helped to uncover gene networks, molecular pathways, and cellular signaling that likely play critical roles in disease development and progression. On the other hand, despite the great promise, many challenges remain in the usage of iPSC-derived neurons for modeling neuropsychiatric disorders, for example, how to generate relatively homogenous populations of specific neuronal subtypes that are affected in a particular disorder and how to better address the genetic heterogeneity that exists in the patient population.