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Gaucher disease (GD) is caused by insufficient activity of acid $\$-glucosidase (GCase) resulting from mutations in GBA1. To understand the pathogenesis of the neuronopathic GD,induced pluripotent stem cells (iPSCs) were generated from fibroblasts isolated from three GD type 2 (GD2) and 2 unaffected (normal and GD carrier) individuals. The iPSCs were converted to neural precursor cells (NPCs) which were further differentiated into neurons. Parental GD2 fibroblasts as well as iPSCs,NPCs,and neurons had similar degrees of GCase deficiency. Lipid analyses showed increases of glucosylsphingosine and glucosylceramide in the GD2 cells. In addition,GD2 neurons showed increased $\$-synuclein protein compared to control neurons. Whole cell patch-clamping of the GD2 and control iPSCs-derived neurons demonstrated excitation characteristics of neurons,but intriguingly,those from GD2 exhibited consistently less negative resting membrane potentials with various degree of reduction in action potential amplitudes,sodium and potassium currents. Culture of control neurons in the presence of the GCase inhibitor (conduritol B epoxide) recapitulated these findings,providing a functional link between decreased GCase activity in GD and abnormal neuronal electrophysiological properties. To our knowledge,this study is first to report abnormal electrophysiological properties in GD2 iPSC-derived neurons that may underlie the neuropathic phenotype in Gaucher disease. View Publication

The ability to generate spiral ganglion neurons (SGNs) from stem cells is a necessary prerequisite for development of cell-replacement therapies for sensorineural hearing loss. We present a protocol that directs human embryonic stem cells (hESCs) toward a purified population of otic neuronal progenitors (ONPs) and SGN-like cells. Between 82% and 95% of these cells express SGN molecular markers,they preferentially extend neurites to the cochlear nucleus rather than nonauditory nuclei,and they generate action potentials. The protocol follows an in vitro stepwise recapitulation of developmental events inherent to normal differentiation of hESCs into SGNs,resulting in efficient sequential generation of nonneuronal ectoderm,preplacodal ectoderm,early prosensory ONPs,late ONPs,and cells with cellular and molecular characteristics of human SGNs. We thus describe the sequential signaling pathways that generate the early and later lineage species in the human SGN lineage,thereby better describing key developmental processes. The results indicate that our protocol generates cells that closely replicate the phenotypic characteristics of human SGNs,advancing the process of guiding hESCs to states serving inner-ear cell-replacement therapies and possible next-generation hybrid auditory prostheses. textcopyright Stem Cells Translational Medicine 2017;6:923-936. View Publication

The essential functions of Polycomb Repressive Complex 1 (PRC1) in development and gene silencing are thought to involve long non-coding RNAs (lncRNAs),but few specific lncRNAs that guide PRC1 activity are known. We screened for lncRNAs which co-precipitate with PRC1 from chromatin and found candidates that impact Polycomb Group protein (PcG)-regulated gene expression in vivo. A novel lncRNA from this screen,CAT7,regulates expression and PcG binding at the MNX1 locus during early neuronal differentiation. CAT7 contains a unique tandem repeat domain which shares high sequence similarity to a non-syntenic zebrafish analog,cat7l. Defects caused by interference of cat7l RNA during zebrafish embryogenesis were rescued by human CAT7 RNA,enhanced by interference of a PRC1 component,and suppressed by interference of a known PRC1 target gene,demonstrating cat7l genetically interacts with a PRC1. We propose a model whereby PRC1 acts in concert with specific lncRNAs,and that CAT7/cat7l represent convergent lncRNAs that independently evolved to tune PRC1 repression at individual loci. View Publication

Generation of induced dopaminergic (iDA) neurons may provide a significant step forward towards cell replacement therapy for Parkinson's disease (PD). To study and compare transcriptional programs of induced cells versus primary DA neurons is a preliminary step towards characterizing human iDA neurons. We have optimized a protocol to efficiently generate iDA neurons from human pluripotent stem cells (hPSCs). We then sequenced the transcriptomes of iDA neurons derived from 6 different hPSC lines and compared them to that of primary midbrain (mDA) neurons. We identified a small subset of genes with altered expression in derived iDA neurons from patients with Parkinson's Disease (PD). We also observed that iDA neurons differ significantly from primary mDA neurons in global gene expression,especially in genes related to neuron maturation level. Results suggest iDA neurons from patient iPSCs could be useful for basic and translational studies,including in vitro modeling of PD. However,further refinement of methods of induction and maturation of neurons may better recapitulate full development of mDA neurons from hPSCs. View Publication

Spinal muscular atrophy (SMA) is an inherited neuromuscular disease primarily characterized by degeneration of spinal motor neurons,and caused by reduced levels of the SMN protein. Previous studies to understand the proteomic consequences of reduced SMN have mostly utilized patient fibroblasts and animal models. We have derived human motor neurons from type I SMA and healthy controls by creating their induced pluripotent stem cells (iPSCs). Quantitative mass spectrometry of these cells revealed increased expression of 63 proteins in control motor neurons compared to respective fibroblasts,whereas 30 proteins were increased in SMA motor neurons vs. their fibroblasts. Notably,UBA1 was significantly decreased in SMA motor neurons,supporting evidence for ubiquitin pathway defects. Subcellular distribution of UBA1 was predominantly cytoplasmic in SMA motor neurons in contrast to nuclear in control motor neurons; suggestive of neurodevelopmental abnormalities. Many of the proteins that were decreased in SMA motor neurons,including beta III-tubulin and UCHL1,were associated with neurodevelopment and differentiation. These neuron-specific consequences of SMN depletion were not evident in fibroblasts,highlighting the importance of iPSC technology. The proteomic profiles identified here provide a useful resource to explore the molecular consequences of reduced SMN in motor neurons,and for the identification of novel biomarker and therapeutic targets for SMA. View Publication

Induced pluripotent stem cell (iPSC)-derived cortical neurons potentially present a powerful new model to understand corticogenesis and neurological disease. Previous work has established that differentiation protocols can produce cortical neurons,but little has been done to characterize these at cellular resolution. In particular,it is unclear to what extent in vitro two-dimensional,relatively disordered culture conditions recapitulate the development of in vivo cortical layer identity. Single-cell multiplex reverse transcriptase-quantitative polymerase chain reaction (RT-qPCR) was used to interrogate the expression of genes previously implicated in cortical layer or phenotypic identity in individual cells. Totally,93.6% of single cells derived from iPSCs expressed genes indicative of neuronal identity. High proportions of single neurons derived from iPSCs expressed glutamatergic receptors and synaptic genes. And,68.4% of iPSC-derived neurons expressing at least one layer marker could be assigned to a laminar identity using canonical cortical layer marker genes. We compared single-cell RNA-seq of our iPSC-derived neurons to available single-cell RNA-seq data from human fetal and adult brain and found that iPSC-derived cortical neurons closely resembled primary fetal brain cells. Unexpectedly,a subpopulation of iPSC-derived neurons co-expressed canonical fetal deep and upper cortical layer markers. However,this appeared to be concordant with data from primary cells. Our results therefore provide reassurance that iPSC-derived cortical neurons are highly similar to primary cortical neurons at the level of single cells but suggest that current layer markers,although effective,may not be able to disambiguate cortical layer identity in all cells. View Publication

Increased dosage of methyl-CpG-binding protein-2 (MeCP2) results in a dramatic neurodevelopmental phenotype with onset at birth. We generated induced pluripotent stem cells (iPSCs) from patients with the MECP2 duplication syndrome (MECP2dup),carrying different duplication sizes,to study the impact of increased MeCP2 dosage in human neurons. We show that cortical neurons derived from these different MECP2dup iPSC lines have increased synaptogenesis and dendritic complexity. In addition,using multi-electrodes arrays,we show that neuronal network synchronization was altered in MECP2dup-derived neurons. Given MeCP2 functions at the epigenetic level,we tested whether these alterations were reversible using a library of compounds with defined activity on epigenetic pathways. One histone deacetylase inhibitor,NCH-51,was validated as a potential clinical candidate. Interestingly,this compound has never been considered before as a therapeutic alternative for neurological disorders. Our model recapitulates early stages of the human MECP2 duplication syndrome and represents a promising cellular tool to facilitate therapeutic drug screening for severe neurodevelopmental disorders. View Publication

GTF2IRD1 is one of the three members of the GTF2I gene family,clustered on chromosome 7 within a 1.8 Mb region that is prone to duplications and deletions in humans. Hemizygous deletions cause Williams-Beuren syndrome (WBS) and duplications cause WBS duplication syndrome. These copy number variations disturb a variety of developmental systems and neurological functions. Human mapping data and analyses of knockout mice show that GTF2IRD1 and GTF2I underpin the craniofacial abnormalities,mental retardation,visuospatial deficits and hypersociability of WBS. However,the cellular role of the GTF2IRD1 protein is poorly understood due to its very low abundance and a paucity of reagents. Here,for the first time,we show that endogenous GTF2IRD1 has a punctate pattern in the nuclei of cultured human cell lines and neurons. To probe the functional relationships of GTF2IRD1 in an unbiased manner,yeast two-hybrid libraries were screened,isolating 38 novel interaction partners,which were validated in mammalian cell lines. These relationships illustrate GTF2IRD1 function,as the isolated partners are mostly involved in chromatin modification and transcriptional regulation,whilst others indicate an unexpected role in connection with the primary cilium. Mapping of the sites of protein interaction also indicates key features regarding the evolution of the GTF2IRD1 protein. These data provide a visual and molecular basis for GTF2IRD1 nuclear function that will lead to an understanding of its role in brain,behaviour and human disease. View Publication

Induced pluripotent stem cells (iPSC) and their differentiated derivatives offer a unique source of human primary cells for toxicity screens. Here,we report on the comparative cytotoxicity of 80 compounds (neurotoxicants,developmental neurotoxicants,and environmental compounds) in iPSC as well as isogenic iPSC-derived neural stem cells (NSC),neurons,and astrocytes. All compounds were tested over a 24-h period at 10 and 100$\$,in duplicate,with cytotoxicity measured using the MTT assay. Of the 80 compounds tested,50 induced significant cytotoxicity in at least one cell type; per cell type,32,38,46,and 41 induced significant cytotoxicity in iPSC,NSC,neurons,and astrocytes,respectively. Four compounds (valinomycin,3,3',5,5'-tetrabromobisphenol,deltamethrin,and triphenyl phosphate) were cytotoxic in all four cell types. Retesting these compounds at 1,10,and 100$\$ using the same exposure protocol yielded consistent results as compared with the primary screen. Using rotenone,we extended the testing to seven additional iPSC lines of both genders; no substantial difference in the extent of cytotoxicity was detected among the cell lines. Finally,the cytotoxicity assay was simplified by measuring luciferase activity using lineage-specific luciferase reporter iPSC lines which were generated from the parental iPSC line. This article is part of a Special Issue entitled SI: PSC and the brain. View Publication

RTP801 expression is induced by cellular stress and has a pro-apoptotic function in non-proliferating differentiated cells such as neurons. In several neurodegenerative disorders,including Parkinson's disease and Alzheimer's disease,elevated levels of RTP801 have been observed,which suggests a role for RTP801 in neuronal death. Neuronal death is also a pathological hallmark in Huntington's disease (HD),an inherited neurodegenerative disorder caused by a CAG repeat expansion in the huntingtin gene. Currently,the exact mechanisms underlying mutant huntingtin (mhtt)-induced toxicity are still unclear. Here,we investigated whether RTP801 is involved in (mhtt)-induced cell death. Ectopic exon-1 mhtt elevated RTP801 mRNA and protein levels in nerve growth factor (NGF)-differentiated PC12 cells and in rat primary cortical neurons. In neuronal PC12 cells,mhtt also contributed to RTP801 protein elevation by reducing its proteasomal degradation rate,in addition to promoting RTP801 gene expression. Interestingly,silencing RTP801 expression with short hairpin RNAs (shRNAs) blocked mhtt-induced cell death in NGF-differentiated PC12 cells. However,RTP801 protein levels were not altered in the striatum of Hdh(Q7/Q111) and R6/1 mice,two HD models that display motor deficits but not neuronal death. Importantly,RTP801 protein levels were elevated in both neural telencephalic progenitors differentiated from HD patient-derived induced pluripotent stem cells and in the putamen and cerebellum of human HD postmortem brains. Taken together,our results suggest that RTP801 is a novel downstream effector of mhtt-induced toxicity and that it may be relevant to the human disease. View Publication

3D suspension culture is generally considered a promising method to achieve efficient expansion and controlled differentiation of human pluripotent stem cells (hPSCs). In this work,we focused on developing an integrated culture platform for expansion and neural commitment of hPSCs into neural precursors using 3D suspension conditions and chemically-defined culture media. We evaluated different inoculation methodologies for hPSC expansion as 3D aggregates and characterized the resulting cultures in terms of aggregate size distribution. It was demonstrated that upon single-cell inoculation,after four days of culture,3D aggregates were composed of homogenous populations of hPSC and were characterized by an average diameter of 139 ± 26 μm,which was determined to be the optimal size to initiate neural commitment. Temporal analysis revealed that upon neural specification it is possible to maximize the percentage of neural precursor cells expressing the neural markers Sox1 and Pax6 after nine days of culture. These results highlight our ability to define a robust method for production of hPSC-derived neural precursors that minimizes processing steps and that constitutes a promising alternative to the traditional planar adherent culture system due to a high potential for scaling-up. View Publication

For diseases of the brain,the pig (Sus scrofa) is increasingly being used as a model organism that shares many anatomical and biological similarities with humans. We report that pig induced pluripotent stem cells (iPSC) can recapitulate events in early mammalian neural development. Pig iPSC line (POU5F1(high)/SSEA4(low)) had a higher potential to form neural rosettes (NR) containing neuroepithelial cells than either POU5F1(low)/SSEA4(low) or POU5F1(low)/SSEA4(high) lines. Thus,POU5F1 and SSEA4 pluripotency marker profiles in starting porcine iPSC populations can predict their propensity to form more robust NR populations in culture. The NR were isolated and expanded in vitro,retaining their NR morphology and neuroepithelial molecular properties. These cells expressed anterior central nervous system fate markers OTX2 and GBX2 through at least seven passages,and responded to retinoic acid,promoting a more posterior fate (HOXB4+,OTX2-,and GBX2-). These findings offer insight into pig iPSC development,which parallels the human iPSC in both anterior and posterior neural cell fates. These in vitro similarities in early neural differentiation processes support the use of pig iPSC and differentiated neural cells as a cell therapy in allogeneic porcine neural injury and degeneration models,providing relevant translational data for eventual human neural cell therapies. View Publication