Potentially pathogenic alterations have been identified in individuals with autism spectrum disorders (ASDs) within a variety of key neurodevelopment genes. While this hints at a common ASD molecular etiology, gaps persist in our understanding of the neurodevelopmental mechanisms impacted by genetic variants enriched in ASD patients. Induced pluripotent stem cells (iPSCs) can model neurodevelopment in vitro, permitting the characterization of pathogenic mechanisms that manifest during corticogenesis. Taking this approach, we examined the transcriptional differences between iPSC-derived cortical neurons from patients with idiopathic ASD and unaffected controls over a 135-day course of neuronal differentiation. Our data show ASD-specific misregulation of genes involved in neuronal differentiation, axon guidance, cell migration, DNA and RNA metabolism, and neural region patterning. Furthermore, functional analysis revealed defects in neuronal migration and electrophysiological activity, providing compelling support for the transcriptome analysis data. This study reveals important and functionally validated insights into common processes altered in early neuronal development and corticogenesis and may contribute to ASD pathogenesis.

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Autism Spectrum Disorder (ASD) is a behaviorally defined neurodevelopmental condition. Symptoms of ASD cover the spectrum from mild qualitative differences in social interaction to severe communication and social and behavioral challenges that require lifelong support. Attempts at understanding the pathophysiology of ASD have been hampered by a multifactorial etiology that stretches the limits of current behavioral and cell based models. Recent progress has implicated numerous autism-risk genes but efforts to gain a better understanding of the underlying biological mechanisms have seen slow progress. This is in part due to lack of appropriate models for complete molecular and pharmacological studies. The advent of induced pluripotent stem cells (iPSC) has reinvigorated efforts to establish more complete model systems that more reliably identify molecular pathways and predict effective drug targets and candidates in ASD. iPSCs are particularly appealing because they can be derived from human patients and controls for research purposes and provide a technology for the development of a personalized treatment regimen for ASD patients. The pluripotency of iPSCs allow them to be reprogrammed into a number of CNS cell types and phenotypically screened across many patients. This quality is already being exploited in protocols to generate 2-dimensional (2-D) and three-dimensional (3-D) models of neurons and developing brain structures. iPSC models make powerful platforms that can be interrogated using electrophysiology, gene expression studies, and other cell-based quantitative assays. iPSC technology has limitations but when combined with other model systems has great potential for helping define the underlying pathophysiology of ASD. Autism Res 2016, 9: 513-535. © 2015 International Society for Autism Research, Wiley Periodicals, Inc.

Autism spectrum disorder (ASD) is a neurological condition characterized by alterations in social interaction and communication, and restricted and/or repetitive behaviors. The classical type II cadherins cadherin-8 (Cdh8, CDH8) and cadherin-11 (Cdh11, CDH11) have been implicated as autism risk gene candidates. To explore the role of cadherins in the etiology of autism, we investigated their expression patterns during mouse brain development and in autismspecific human tissue. In mice, expression of cadherin-8 and cadherin-11 was developmentally regulated and enriched in the cortex, hippocampus, and thalamus/striatum during the peak of dendrite formation and synaptogenesis. Both cadherins were expressed in synaptic compartments but only cadherin-8 associated with the excitatory synaptic marker neuroligin-1. Induced pluripotent stem cell (iPSC)-derived cortical neural precursor cells (NPCs) and cortical organoids generated from individuals with autism showed upregulated CDH8 expression levels while CDH11 expression levels were downregulated. We used Cdh11 knockout mice of both sexes to analyze the function of cadherin-11, which could help explain phenotypes observed in autism. Cdh11 -/hippocampal neurons exhibited increased dendritic complexity along with altered neuronal and synaptic activity. Similar to the expression profiles in human tissue, levels of cadherin-8 were significantly elevated in Cdh11 knockout brains. Additionally, excitatory synaptic markers neuroligin-1 and PSD-95 were both increased. Together, these results strongly suggest that cadherin-11 is involved in regulating the development of neuronal circuitry and that alterations in the expression levels of cadherin-11 may contribute to the etiology of autism. Cadherin-11 in Neurodevelopment and Autism 2 Significance StatementAutism is a neurodevelopmental condition with high genetic and phenotypic heterogeneity.Multiple genes have been implicated in autism, including the cadherin superfamily of adhesion molecules, cadherin-8 and cadherin-11. This study first characterizes the expression profiles of cadherin-8 and cadherin-11 to understand the potential roles they play in the development of neurons. The study further describes novel contributions of cadherin-11 in neural circuit formation. Loss of cadherin-11 in mice results in altered levels of several synaptic proteins, including PSD-95, neuroligin-1, and cadherin-8, and changes the morphology and activity of excitatory neurons. The levels of cadherin-8 and cadherin-11 in human cells of autistic individuals are both altered, strengthening the hypothesis that these two cadherins may involve in aspects of autism etiology.

Although a number of in vitro disease models have been developed using hiPSCs, one limitation is that these two-dimensional (2-D) systems may not represent the underlying cytoarchitectural and functional complexity of the affected individuals carrying suspected disease variants. Conventional 2-D models remain incomplete representations of in vivo-like structures and do not adequately capture the complexity of the brain. Thus, there is an emerging need for more 3-D hiPSC-based models that can better recapitulate the cellular interactions and functions seen in an in vivo system. Here we report a protocol to develop a 3-D system from undifferentiated hiPSCs based on the serum free embryoid body (SFEB). This 3-D model mirrors aspects of a developing ventralized neocortex and allows for studies into functions integral to living neural cells and intact tissue such as migration, connectivity, communication, and maturation. Specifically, we demonstrate that the SFEBs using our protocol can be interrogated using physiologically relevant and high-content cell based assays such as calcium imaging, and multi-electrode array (MEA) recordings without cryosectioning. In the case of MEA recordings, we demonstrate that SFEBs increase both spike activity and network-level bursting activity during long-term culturing. This SFEB protocol provides a robust and scalable system for the study of developing network formation in a 3-D model that captures aspects of early cortical development.