Understanding the development and dysfunction of the human brain is a major goal of neurobiology. Much of our current understanding of human brain development has been derived from the examination of ...post-mortem and pathological specimens, bolstered by observations of developing non-human primates and experimental studies focused largely on mouse models. However, these tissue specimens and model systems cannot fully capture the unique and dynamic features of human brain development. Recent advances in stem cell technologies that enable the generation of human brain organoids from pluripotent stem cells (PSCs) promise to profoundly change our understanding of the development of the human brain and enable a detailed study of the pathogenesis of inherited and acquired brain diseases.
Despite the clinical and genetic heterogeneity of autism, bulk gene expression studies show that changes in the neocortex of autism patients converge on common genes and pathways. However, direct ...assessment of specific cell types in the brain affected by autism has not been feasible until recently. We used single-nucleus RNA sequencing of cortical tissue from patients with autism to identify autism-associated transcriptomic changes in specific cell types. We found that synaptic signaling of upper-layer excitatory neurons and the molecular state of microglia are preferentially affected in autism. Moreover, our results show that dysregulation of specific groups of genes in cortico-cortical projection neurons correlates with clinical severity of autism. These findings suggest that molecular changes in upper-layer cortical circuits are linked to behavioral manifestations of autism.
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.
The size and surface area of the mammalian brain are thought to be critical determinants of intellectual ability. Recent studies show that development of the gyrated human neocortex involves a ...lineage of neural stem and transit-amplifying cells that forms the outer subventricular zone (OSVZ), a proliferative region outside the ventricular epithelium. We discuss how proliferation of cells within the OSVZ expands the neocortex by increasing neuron number and modifying the trajectory of migrating neurons. Relating these features to other mammalian species and known molecular regulators of the mouse neocortex suggests how this developmental process could have emerged in evolution.
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.
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.
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.
Directed differentiation from human pluripotent stem cells (hPSCs) has seen significant progress in recent years. However, most differentiated populations exhibit immature properties of an early ...embryonic stage, raising concerns about their ability to model and treat disease. Here, we report the directed differentiation of hPSCs into medial ganglionic eminence (MGE)-like progenitors and their maturation into forebrain type interneurons. We find that early-stage progenitors progress via a radial glial-like stem cell enriched in the human fetal brain. Both in vitro and posttransplantation into the rodent cortex, the MGE-like cells develop into GABAergic interneuron subtypes with mature physiological properties along a prolonged intrinsic timeline of up to 7 months, mimicking endogenous human neural development. MGE-derived cortical interneuron deficiencies are implicated in a broad range of neurodevelopmental and degenerative disorders, highlighting the importance of these results for modeling human neural development and disease.
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•hPSC-derived MGE-like GABAergic interneurons model human neural development•MGE-like progenitors display human-enriched radial glial stem cell complexity•MGE-like cells exhibit protracted maturation into functional interneuron subtypes•MGE-like cells mature and functionally integrate postinjection in the mouse brain
Directed differentiation of hPSC-derived GABAergic interneurons progress along a prolonged intrinsic timeline that mirrors stages of human postnatal development.
Challenges of Organoid Research Andrews, Madeline G; Kriegstein, Arnold R
Annual review of neuroscience,
07/2022, Volume:
45, Issue:
1
Journal Article
Peer reviewed
Open access
Organoids are 3D cell culture systems derived from human pluripotent stem cells that contain tissue resident cell types and reflect features of early tissue organization. Neural organoids are a ...particularly innovative scientific advance given the lack of accessibility of developing human brain tissue and intractability of neurological diseases. Neural organoids have become an invaluable approach to model features of human brain development that are not well reflected in animal models. Organoids also hold promise for the study of atypical cellular, molecular, and genetic features that underscore neurological diseases. Additionally, organoids may provide a platform for testing therapeutics in human cells and are a potential source for cell replacement approaches to brain injury or disease. Despite the promising features of organoids, their broad utility is tempered by a variety of limitations yet to be overcome, including lack of high-fidelity cell types, limited maturation, atypical physiology, and lack of arealization, features that may limit their reliability for certain applications.
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