The recent outbreak of Zika virus (ZIKV) in Brazil has been linked to substantial increases in fetal abnormalities and microcephaly. However, information about the underlying molecular and cellular ...mechanisms connecting viral infection to these defects remains limited. In this study we have examined the expression of receptors implicated in cell entry of several enveloped viruses including ZIKV across diverse cell types in the developing brain. Using single-cell RNA-seq and immunohistochemistry, we found that the candidate viral entry receptor AXL is highly expressed by human radial glial cells, astrocytes, endothelial cells, and microglia in developing human cortex and by progenitor cells in developing retina. We also show that AXL expression in radial glia is conserved in developing mouse and ferret cortex and in human stem cell-derived cerebral organoids, highlighting multiple experimental systems that could be applied to study mechanisms of ZIKV infectivity and effects on brain development.
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•Single-cell analysis reveals expression and specificity of candidate Zika receptors•AXL shows strong expression in human radial glia, brain capillaries, and microglia•Developing human retina progenitors also show high AXL expression•AXL expression is conserved in rodents and human cerebral organoid model systems
The recent outbreak of Zika virus and the association with fetal abnormalities including microcephaly represents a global health emergency. Kriegstein and colleagues survey the expression of candidate Zika virus entry proteins to suggest that high AXL expression in neural stem cells may render this population selectively vulnerable to viral infection.
The classic view of cortical development, embodied in the radial unit hypothesis, highlights the ventricular radial glia (vRG) scaffold as a key architectonic feature of the developing neocortex. The ...scaffold includes continuous fibers spanning the thickness of the developing cortex during neurogenesis across mammals. However, we find that in humans, the scaffold transforms into a physically discontinuous structure during the transition from infragranular to supragranular neuron production. As a consequence of this transformation, supragranular layer neurons arrive at their terminal positions in the cortical plate along outer radial glia (oRG) cell fibers. In parallel, the radial glia that contact the ventricle develop distinct gene expression profile and “truncated” morphology. We propose a supragranular layer expansion hypothesis that posits a deterministic role of oRG cells in the radial and tangential expansion of supragranular layers in primates, with implications for patterns of neuronal migration, area patterning, and cortical folding.
•The radial glia scaffold of the human brain becomes discontinuous at mid-neurogenesis•Radial glia along the ventricle develop truncated fibers and a distinct molecular identity•The radial glia scaffold is discontinuous during supragranular layer neurogenesis
Radial glia fibers form a physical scaffold that supports neuronal migration during neurogenesis. During human neurogenesis, this scaffold transforms into a physically discontinuous structure formed by two morphologically and molecularly distinct radial glia subtypes: truncated and outer radial glia.
Radial glia, the neural stem cells of the neocortex, are located in two niches: the ventricular zone and outer subventricular zone. Although outer subventricular zone radial glia may generate the ...majority of human cortical neurons, their molecular features remain elusive. By analyzing gene expression across single cells, we find that outer radial glia preferentially express genes related to extracellular matrix formation, migration, and stemness, including TNC, PTPRZ1, FAM107A, HOPX, and LIFR. Using dynamic imaging, immunostaining, and clonal analysis, we relate these molecular features to distinctive behaviors of outer radial glia, demonstrate the necessity of STAT3 signaling for their cell cycle progression, and establish their extensive proliferative potential. These results suggest that outer radial glia directly support the subventricular niche through local production of growth factors, potentiation of growth factor signals by extracellular matrix proteins, and activation of self-renewal pathways, thereby enabling the developmental and evolutionary expansion of the human neocortex.
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•oRG and vRG cells represent molecularly distinct subpopulations of human radial glia•oRG transcriptional state first emerges in VZ during early cortical development•Single oRG cells generate hundreds of daughter cells of diverse types•Molecular profile suggests that oRG cells sustain proliferative niche in primate OSVZ
Single-cell transcriptomics reveals molecular distinctions between human radial glia residing in the ventricular and outer subventricular zones, suggesting that outer radial glia may generate a self-sustaining proliferative niche that supports primate brain expansion during development of the cerebral cortex.
The human cortex comprises diverse cell types that emerge from an initially uniform neuroepithelium that gives rise to radial glia, the neural stem cells of the cortex. To characterize the earliest ...stages of human brain development, we performed single-cell RNA-sequencing across regions of the developing human brain, including the telencephalon, diencephalon, midbrain, hindbrain and cerebellum. We identify nine progenitor populations physically proximal to the telencephalon, suggesting more heterogeneity than previously described, including a highly prevalent mesenchymal-like population that disappears once neurogenesis begins. Comparison of human and mouse progenitor populations at corresponding stages identifies two progenitor clusters that are enriched in the early stages of human cortical development. We also find that organoid systems display low fidelity to neuroepithelial and early radial glia cell types, but improve as neurogenesis progresses. Overall, we provide a comprehensive molecular and spatial atlas of early stages of human brain and cortical development.
Abstract
Aims
Inflammation is an important driver of hypertension. Periodontitis is a chronic inflammatory disease, which could provide a mechanism for pro-hypertensive immune activation, but ...evidence of a causal relationship in humans is scarce. We aimed to investigate the nature of the association between periodontitis and hypertension.
Methods and results
We performed a two-sample Mendelian randomization analysis in the ∼750 000 UK-Biobank/International Consortium of Blood Pressure-Genome-Wide Association Studies participants using single nucleotide polymorphisms (SNPs) in SIGLEC5, DEFA1A3, MTND1P5, and LOC107984137 loci GWAS-linked to periodontitis, to ascertain their effect on blood pressure (BP) estimates. This demonstrated a significant relationship between periodontitis-linked SNPs and BP phenotypes. We then performed a randomized intervention trial on the effects of treatment of periodontitis on BP. One hundred and one hypertensive patients with moderate/severe periodontitis were randomized to intensive periodontal treatment (IPT; sub- and supragingival scaling/chlorhexidine; n = 50) or control periodontal treatment (CPT; supragingival scaling; n = 51) with mean ambulatory 24-h (ABPM) systolic BP (SBP) as primary outcome. Intensive periodontal treatment improved periodontal status at 2 months, compared to CPT. This was accompanied by a substantial reduction in mean SBP in IPT compared to the CPT (mean difference of −11.1 mmHg; 95% CI 6.5–15.8; P < 0.001). Systolic BP reduction was correlated to periodontal status improvement. Diastolic BP and endothelial function (flow-mediated dilatation) were also improved by IPT. These cardiovascular changes were accompanied by reductions in circulating IFN-γ and IL-6 as well as activated (CD38+) and immunosenescent (CD57+CD28null) CD8+T cells, previously implicated in hypertension.
Conclusion
A causal relationship between periodontitis and BP was observed providing proof of concept for development of clinical trial in a large cohort of hypertensive patients. ClinicalTrials.gov: NCT02131922.
Long non-coding RNAs (lncRNAs) are a diverse and poorly conserved category of transcripts that have expanded greatly in primates, particularly in the brain. We identified an lncRNA, which has ...acquired 16 microRNA response elements for miR-143-3p in the Catarrhini branch of primates. This lncRNA, termed LncND (neurodevelopment), is expressed in neural progenitor cells and then declines in neurons. Binding and release of miR-143-3p by LncND control the expression of Notch receptors. LncND expression is enriched in radial glia cells (RGCs) in the ventricular and subventricular zones of developing human brain. Downregulation in neuroblastoma cells reduced cell proliferation and induced neuronal differentiation, an effect phenocopied by miR-143-3p overexpression. Gain of function of LncND in developing mouse cortex led to an expansion of PAX6+ RGCs. These findings support a role for LncND in miRNA-mediated regulation of Notch signaling within the neural progenitor pool in primates that may have contributed to the expansion of cerebral cortex.
•Identification of LncND with a Catarrhine insertion of 16 MREs for miR-143-3p•LncND regulates expression of Notch genes by sequestering miR-143-3p•High expression of LncND in radial glia cells in human VZ and OSVZ•LncND appears to be involved in the expansion of radial glia cells in primates
Rani et al. demonstrate the function of a primate lncRNA, designated LncND, as a miRNA reservoir regulating the expression of Notch-1 and Notch-2 by sequestering miR-143-3p. They provide evidence for the involvement of LncND in primate brain expansion.
Adult cortical areas consist of specialized cell types and circuits that support unique higher-order cognitive functions. How this regional diversity develops from an initially uniform ...neuroepithelium has been the subject of decades of seminal research, and emerging technologies, including single-cell transcriptomics, provide a new perspective on area-specific molecular diversity. Here, we review the early developmental processes that underlie cortical arealization, including both cortex intrinsic and extrinsic mechanisms as embodied by the protomap and protocortex hypotheses, respectively. We propose an integrated model of serial homology whereby intrinsic genetic programs and local factors establish early transcriptomic differences between excitatory neurons destined to give rise to broad “proto-regions,” and activity-dependent mechanisms lead to progressive refinement and formation of sharp boundaries between functional areas. Finally, we explore the potential of these basic developmental processes to inform our understanding of the emergence of functional neural networks and circuit abnormalities in neurodevelopmental disorders.
Cadwell et al. review the early developmental processes that underlie arealization of the cerebral cortex, with a focus on recent single-cell transcriptomic studies, the interplay of intrinsic genetic programs and extrinsic signals, and implications for developmental of functional circuits.
Classical lissencephaly is a genetic neurological disorder associated with mental retardation and intractable epilepsy, and Miller-Dieker syndrome (MDS) is the most severe form of the disease. In ...this study, to investigate the effects of MDS on human progenitor subtypes that control neuronal output and influence brain topology, we analyzed cerebral organoids derived from control and MDS-induced pluripotent stem cells (iPSCs) using time-lapse imaging, immunostaining, and single-cell RNA sequencing. We saw a cell migration defect that was rescued when we corrected the MDS causative chromosomal deletion and severe apoptosis of the founder neuroepithelial stem cells, accompanied by increased horizontal cell divisions. We also identified a mitotic defect in outer radial glia, a progenitor subtype that is largely absent from lissencephalic rodents but critical for human neocortical expansion. Our study, therefore, deepens our understanding of MDS cellular pathogenesis and highlights the broad utility of cerebral organoids for modeling human neurodevelopmental disorders.
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•Cortical organoids from control and MDS patient-derived iPSCs model lissencephaly•Neural stem cells in MDS organoids show increased apoptosis and horizontal divisions•Deep-layer neurons are more abundant in MDS organoids than in controls•Outer radial glia-like cells forming in MDS organoids show a mitotic delay
Bershteyn and colleagues show that cerebral organoid modeling of lissencephaly using iPSCs derived from Miller-Dieker syndrome patients can characterize cellular and neurodevelopmental disease phenotypes and identify a mitotic defect in outer radial glia, a cell type that is particularly important for human cortical development.
Systematic analyses of spatiotemporal gene expression trajectories during organogenesis have been challenging because diverse cell types at different stages of maturation and differentiation coexist ...in the emerging tissues. We identified discrete cell types as well as temporally and spatially restricted trajectories of radial glia maturation and neurogenesis in developing human telencephalon. These lineage-specific trajectories reveal the expression of neurogenic transcription factors in early radial glia and enriched activation of mammalian target of rapamycin signaling in outer radial glia. Across cortical areas, modest transcriptional differences among radial glia cascade into robust typological distinctions among maturing neurons. Together, our results support a mixed model of topographical, typological, and temporal hierarchies governing cell-type diversity in the developing human telencephalon, including distinct excitatory lineages emerging in rostral and caudal cerebral cortex.
Direct comparisons of human and non-human primate brains can reveal molecular pathways underlying remarkable specializations of the human brain. However, chimpanzee tissue is inaccessible during ...neocortical neurogenesis when differences in brain size first appear. To identify human-specific features of cortical development, we leveraged recent innovations that permit generating pluripotent stem cell-derived cerebral organoids from chimpanzee. Despite metabolic differences, organoid models preserve gene regulatory networks related to primary cell types and developmental processes. We further identified 261 differentially expressed genes in human compared to both chimpanzee organoids and macaque cortex, enriched for recent gene duplications, and including multiple regulators of PI3K-AKT-mTOR signaling. We observed increased activation of this pathway in human radial glia, dependent on two receptors upregulated specifically in human: INSR and ITGB8. Our findings establish a platform for systematic analysis of molecular changes contributing to human brain development and evolution.
•Brain organoids preserve gene expression networks despite elevated metabolic stress•Chimpanzee organoids enable studies of the evolution of human brain development•Primary and organoid samples reveal 261 human-specific gene expression changes•Human radial glia exhibit increased mTOR activation compared to non-human primates
Comparisons of cerebral organoids between chimpanzees, macaques, and humans reveal gene duplications and cell-signaling alterations that explain developmental evolutionary differences that are unique to us as a species.
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