Dysregulation of the chromatin environment leads to differential alternative splicing as a mechanism of disease in a human model of autism spectrum disorder.

Autism spectrum disorder (ASD) affects 1 in 44 children. Chromatin regulatory proteins are overrepresented among genes that contain high risk variants in ASD. Disruption of the chromatin environment leads to widespread dysregulation of gene expression, which is traditionally thought of as a mechanism of disease pathogenesis associated with ASD. Alternatively, alterations in chromatin dynamics could also lead to dysregulation of alternative splicing, which is understudied as a mechanism of ASD pathogenesis. The anticonvulsant valproic acid (VPA) is a well-known environmental risk factor for ASD that acts as a class I histone deacetylase inhibitor. However, the precise molecular mechanisms underlying defects in human neuronal development associated with exposure to VPA are understudied. To dissect how VPA exposure and subsequent chromatin hyperacetylation influence molecular signatures involved in ASD pathogenesis, we conducted RNA sequencing (RNA-seq) in human cortical neurons that were treated with VPA. We observed that differentially expressed genes (DEGs) were enriched for mRNA splicing, mRNA processing, histone modification and metabolism related gene sets. Furthermore, we observed widespread increases in the number and the type of alternative splicing events. Analysis of differential transcript usage (DTU) showed that exposure to VPA induces extensive alterations in transcript isoform usage across neurodevelopmentally important genes. Finally, we find that DEGs and genes that display DTU overlap with known ASD-risk genes. Altogether, these findings suggest that, in addition to differential gene expression, changes in alternative splicing correlated with alterations in the chromatin environment could act as an additional mechanism of disease in ASD.

Convergence of human cellular models and genetics to study neural stem cell signaling to enhance central nervous system regeneration and repair.

Human central nervous system (CNS) regeneration is considered the holy grail of neuroscience research, and is one of the most pressing and difficult questions in biology and science. Despite more than 20 years of work in the field of neural stem cells (NSCs), the area remains in its infancy as our understanding of the fundamental mechanisms that can be leveraged to improve CNS regeneration in neurological diseases is still growing. Here, we focus on the recent lessons from lower organism CNS regeneration genetics and how such findings are starting to illuminate our understanding of NSC signaling pathways in humans. These findings will allow us to improve upon our knowledge of endogenous NSC function, the utility of exogenous NSCs, and the limitations of NSCs as therapeutic vehicles for providing relief from devastating human neurological diseases. We also discuss the limitations of activating NSC signaling for CNS repair in humans, especially the potential for tumor formation. Finally, we will review the recent advances in new culture techniques, including patient-derived cells and cerebral organoids to model the genetic regulation of signaling pathways controlling the function of NSCs during injury and disease states.

Venous thromboembolism in children with central nervous system tumors: Comparison of an institutional cohort to a national administrative database.

BACKGROUND: Central nervous system (CNS) tumors are the second most common malignancy of childhood, and published data on venous thromboembolism (VTE) rate and risk factors for these patients are outdated or incomplete. Here, we determine the cumulative incidence and risk factors for VTE in this population. PROCEDURE: VTE diagnosis and associated clinical risk factors were abstracted and analyzed for two cohorts of children (0-21 years) diagnosed with CNS tumors between January 1, 2010 to September 30, 2018. The first study was a retrospective single institution cohort study. The initial observations were confirmed across multiple pediatric hospitals using the Pediatric Health Information System (PHIS) administrative database. RESULTS: The single-institution cohort included 338 patients aged 3 days to 20.9 years (median age, 8.6 years); VTE developed in eight (2.4%) patients. The PHIS cohort included 17 634 patients aged from 0 to 21.9 years (median: 9.5 years); VTE developed in 354 (2.0%) patients. Univariate analysis for the single-institution cohort identified central venous catheter (CVC) placement as a risk factor for VTE (odds ratio [OR] 8.40, 95% confidence interval [CI] 1.43-49.41, P = .0186). Multivariable analysis of the PHIS dataset identified CVC placement (OR 1.97, 95% CI 1.57-2.46; P < .0001), obesity (OR 2.96, 95% CI 1.21-7.26; P = .0177), and more than one hospital admission (OR 3.54, 95% CI 2.69-4.64; P < .0001) as significant predictors of VTE. VTE diagnosis was not associated with increased mortality in either cohort. CONCLUSIONS: The VTE rate in children with CNS tumors is low (2%). CVC placement was identified as a modifiable risk factor in both cohorts.

Patient-derived organoids recapitulate glioma-intrinsic immune program and progenitor populations of glioblastoma.

Glioblastoma multiforme (GBM) is a highly lethal human cancer thought to originate from a self-renewing and therapeutically-resistant population of glioblastoma stem cells (GSCs). The intrinsic mechanisms enacted by GSCs during 3D tumor formation, however, remain unclear, especially in the stages prior to angiogenic/immunological infiltration. In this study, we performed a deep characterization of the genetic, immune, and metabolic profiles of GBM organoids from several patient-derived GSCs (GBMO). Despite being devoid of immune cells, transcriptomic analysis across GBMO revealed a surprising immune-like molecular program, enriched in cytokine, antigen presentation and processing, T-cell receptor inhibitors, and interferon genes. We find two important cell populations thought to drive GBM progression, Special AT-rich sequence-binding protein 2 (SATB2+) and homeodomain-only protein homeobox (HOPX+) progenitors, contribute to this immune landscape in GBMO and GBM in vivo. These progenitors, but not other cell types in GBMO, are resistant to conventional GBM therapies, temozolomide and irradiation. Our work defines a novel intrinsic immune-like landscape in GBMO driven, in part, by SATB2+ and HOPX+ progenitors and deepens our understanding of the intrinsic mechanisms utilized by GSCs in early GBM formation.

Conserved Cis-Acting Range Extender Element Mediates Extreme Long-Range Enhancer Activity in Mammals.

While most mammalian enhancers regulate their cognate promoters over moderate distances of tens of kilobases (kb), some enhancers act over distances in the megabase range. The sequence features enabling such extreme-distance enhancer-promoter interactions remain elusive. Here, we used in vivo enhancer replacement experiments in mice to show that short- and medium-range enhancers cannot initiate gene expression at extreme-distance range. We uncover a novel conserved cis-acting element, Range EXtender (REX), that confers extreme-distance regulatory activity and is located next to a long-range enhancer of Sall1. The REX element itself has no endogenous enhancer activity. However, addition of the REX to other short- and mid-range enhancers substantially increases their genomic interaction range. In the most extreme example observed, addition of the REX increased the range of an enhancer by an order of magnitude, from its native 71kb to 840kb. The REX element contains highly conserved [C/T]AATTA homeodomain motifs. These motifs are enriched around long-range limb enhancers genome-wide, including the ZRS, a benchmark long-range limb enhancer of Shh. Mutating the [C/T]AATTA motifs within the ZRS does not affect its limb-specific enhancer activity at short range, but selectively abolishes its long-range activity, resulting in severe limb reduction in knock-in mice. In summary, we identify a sequence signature globally associated with long-range enhancer-promoter interactions and describe a prototypical REX element that is necessary and sufficient to confer extreme-distance gene activation by remote enhancers.

Stat1 is an inducible transcriptional repressor of neural stem cells self-renewal program during neuroinflammation.

A central issue in regenerative medicine is understanding the mechanisms that regulate the self-renewal of endogenous stem cells in response to injury and disease. Interferons increase hematopoietic stem cells during infection by activating STAT1, but the mechanisms by which STAT1 regulates intrinsic programs in neural stem cells (NSCs) during neuroinflammation is less known. Here we explored the role of STAT1 on NSC self-renewal. We show that overexpressing Stat1 in NSCs derived from the subventricular zone (SVZ) decreases NSC self-renewal capacity while Stat1 deletion increases NSC self-renewal, neurogenesis, and oligodendrogenesis in isolated NSCs. Importantly, we find upregulation of STAT1 in NSCs in a mouse model of multiple sclerosis (MS) and an increase in pathological T cells expressing IFN-γ rather than interleukin 17 (IL-17) in the cerebrospinal fluid of affected mice. We find IFN-γ is superior to IL-17 in reducing proliferation and precipitating an abnormal NSC phenotype featuring increased STAT1 phosphorylation and Stat1 and p16ink4a gene expression. Notably, Stat1-/- NSCs were resistant to the effect of IFN-γ. Lastly, we identified a Stat1-dependent gene expression profile associated with an increase in the Sox9 transcription factor, a regulator of self-renewal. Stat1 binds and transcriptionally represses Sox9 in a transcriptional luciferase assay. We conclude that Stat1 serves as an inducible checkpoint for NSC self-renewal that is upregulated during chronic brain inflammation leading to decreased self-renewal. As such, Stat1 may be a potential target to modulate for next generation therapies to prevent progression and loss of repair function in NSCs/neural progenitors in MS.

Rapid and Quantitative Functional Interrogation of Human Enhancer Variant Activity in Live Mice.

Functional analysis of non-coding variants associated with human congenital disorders remains challenging due to the lack of efficient in vivo models. Here we introduce dual-enSERT, a robust Cas9-based two-color fluorescent reporter system which enables rapid, quantitative comparison of enhancer allele activities in live mice of any genetic background. We use this new technology to examine and measure the gain- and loss-of-function effects of enhancer variants linked to limb polydactyly, autism, and craniofacial malformation. By combining dual-enSERT with single-cell transcriptomics, we characterize variant enhancer alleles at cellular resolution, thereby implicating candidate molecular pathways in pathogenic enhancer misregulation. We further show that independent, polydactyly-linked enhancer variants lead to ectopic expression in the same cell populations, indicating shared genetic mechanisms underlying non-coding variant pathogenesis. Finally, we streamline dual-enSERT for analysis in F0 animals by placing both reporters on the same transgene separated by a synthetic insulator. Dual-enSERT allows researchers to go from identifying candidate enhancer variants to analysis of comparative enhancer activity in live embryos in under two weeks.

A noncoding single-nucleotide polymorphism at 8q24 drives IDH1-mutant glioma formation.

Establishing causal links between inherited polymorphisms and cancer risk is challenging. Here, we focus on the single-nucleotide polymorphism rs55705857, which confers a sixfold greater risk of isocitrate dehydrogenase (IDH)-mutant low-grade glioma (LGG). We reveal that rs55705857 itself is the causal variant and is associated with molecular pathways that drive LGG. Mechanistically, we show that rs55705857 resides within a brain-specific enhancer, where the risk allele disrupts OCT2/4 binding, allowing increased interaction with the Myc promoter and increased Myc expression. Mutating the orthologous mouse rs55705857 locus accelerated tumor development in an Idh1R132H-driven LGG mouse model from 472 to 172 days and increased penetrance from 30% to 75%. Our work reveals mechanisms of the heritable predisposition to lethal glioma in ~40% of LGG patients.

Electrophysiological Maturation of Cerebral Organoids Correlates with Dynamic Morphological and Cellular Development.

Cerebral organoids (COs) are rapidly accelerating the rate of translational neuroscience based on their potential to model complex features of the developing human brain. Several studies have examined the electrophysiological and neural network features of COs; however, no study has comprehensively investigated the developmental trajectory of electrophysiological properties in whole-brain COs and correlated these properties with developmentally linked morphological and cellular features. Here, we profiled the neuroelectrical activities of COs over the span of 5 months with a multi-electrode array platform and observed the emergence and maturation of several electrophysiologic properties, including rapid firing rates and network bursting events. To complement these analyses, we characterized the complex molecular and cellular development that gives rise to these mature neuroelectrical properties with immunohistochemical and single-cell transcriptomic analyses. This integrated approach highlights the value of COs as an emerging model system of human brain development and neurological disease.

Combined administration of MK-801 and cycloheximide produces a delayed potentiation of fear discrimination memory extinction.

Mixed evidence exists regarding the role of N-methyl-D-aspartate (NMDA) receptors in memory reconsolidation. We provide no evidence that NMDA receptors are involved with memory reconsolidation, but instead demonstrate that prereactivation systemic MK-801 injection, combined with postreactivation intrabasolateral amygdala (BLA) cycloheximide infusion, produces a delayed potentiation of extinction learning. These data suggest that an interaction between NMDA antagonism and protein synthesis inhibition may enhance extinction by exerting effects outside of the intended reconsolidation manipulation window. The present work demonstrates a novel pharmacological enhancement of extinction, and underscores the importance of employing proper control procedures in reconsolidation research. (PsycINFO Database Record

iPhemap: an atlas of phenotype to genotype relationships of human iPSC models of neurological diseases.

Disease modeling with induced pluripotent stem cells (iPSCs) is creating an abundance of phenotypic information that has become difficult to follow and interpret. Here, we report a systematic analysis of research practices and reporting bias in neurological disease models from 93 published articles. We find heterogeneity in current research practices and a reporting bias toward certain diseases. Moreover, we identified 663 CNS cell-derived phenotypes from 243 patients and 214 controls, which varied by mutation type and developmental stage in vitro We clustered these phenotypes into a taxonomy and characterized these phenotype-genotype relationships to generate a phenogenetic map that revealed novel correlations among previously unrelated genes. We also find that alterations in patient-derived molecular profiles associated with cellular phenotypes, and dysregulated genes show predominant expression in brain regions with pathology. Last, we developed the iPS cell phenogenetic map project atlas (iPhemap), an open submission, online database to continually catalog disease phenotypes. Overall, our findings offer new insights into the phenogenetics of iPSC-derived models while our web tool provides a platform for researchers to query and deposit phenotypic information of neurological diseases.