Dividing Precursor Cells of the Embryonic Cortical Ventricular Zone Have Morphological and Molecular Characteristics of Radial Glia

The Journal of Neuroscience : the Official Journal of the Society for Neuroscience. Apr, 2002  |  Pubmed ID: 11943818

The embryonic ventricular zone (VZ) of the cerebral cortex contains migrating neurons, radial glial cells, and a large population of cycling progenitor cells that generate newborn neurons. The latter two cell classes have been assumed for some time to be distinct in both function and anatomy, but the cellular anatomy of the progenitor cell type has remained poorly defined. Several recent reports have raised doubts about the distinction between radial glial and precursor cells by demonstrating that radial glial cells are themselves neuronal progenitor cells (Malatesta et al., 2000; Hartfuss et al., 2001; Miyata et al., 2001; Noctor et al., 2001). This discovery raises the possibility that radial glia and the population of VZ progenitor cells may be one anatomical and functional cell class. Such a hypothesis predicts that throughout neurogenesis almost all mitotically active VZ cells and a substantial percentage of VZ cells overall are radial glia. We have therefore used various anatomical, immunohistochemical, and electrophysiological techniques to test these predictions. Our data demonstrate that the majority of VZ cells, and nearly all mitotically active VZ cells during neurogenesis, both have radial glial morphology and express radial glial markers. In addition, intracellular dye filling of electrophysiologically characterized progenitor cells in the VZ demonstrates that these cells have the morphology of radial glia. Because the vast majority cycling cells in the cortical VZ have characteristics of radial glia, the radial glial precursor cell may be responsible for both the production of newborn neurons and the guidance of daughter neurons to their destinations in the developing cortex.

Increased Excitability and Decreased Sensitivity to GABA in an Animal Model of Dysplastic Cortex

Epilepsia. Sep, 2002  |  Pubmed ID: 12199722

Cortical dysplasia (CD) is associated with epilepsy in both the pediatric and adult populations. The mechanism underlying seizures with cortical malformations is still poorly understood. To study the physiology of dysplastic cortex, we developed an experimental model of CD.

Is There More to GABA Than Synaptic Inhibition?

Nature Reviews. Neuroscience. Sep, 2002  |  Pubmed ID: 12209120

In the mature brain, GABA (gamma-aminobutyric acid) functions primarily as an inhibitory neurotransmitter. But it can also act as a trophic factor during nervous system development to influence events such as proliferation, migration, differentiation, synapse maturation and cell death. GABA mediates these processes by the activation of traditional ionotropic and metabotropic receptors, and probably by both synaptic and non-synaptic mechanisms. However, the functional properties of GABA receptor signalling in the immature brain are significantly different from, and in some ways opposite to, those found in the adult brain. The unique features of the early-appearing GABA signalling systems might help to explain how GABA acts as a developmental signal.

Developmental Neurotransmitters?

Neuron. Dec, 2002  |  Pubmed ID: 12495613

Previous studies support an early role for neurotransmitter signaling before synaptogenesis, but puzzlingly, a neurological phenotype is absent in embryonic mice that lack vesicular release. Demarque et al. (in this issue of Neuron) now report that early release of transmitter is unconventional in not requiring action potentials, Ca(2+) entry, or vesicle fusion, thus potentially reconciling the discrepancy.

Neurons from Radial Glia: the Consequences of Asymmetric Inheritance

Current Opinion in Neurobiology. Feb, 2003  |  Pubmed ID: 12593980

Recent work suggests that radial glial cells represent many, if not most, of the neuronal progenitors in the developing cortex. Asymmetric cell division of radial glia results in the self-renewal of the radial glial cell and the birth of a neuron. Among the proteins that direct cell fate in Drosophila melanogaster that have known mammalian homologs, Numb is the best candidate to have a similar function in radial glia. During asymmetric divisions of radial glial cells, the basal cell may inherit the radial glial fibre, while the apical cell sequesters the majority of the Numb protein. We suggest two models that make opposite predictions as to whether the radial glia or nascent neuron inherit the radial glial fiber or the majority of the Numb protein.

Radial Glia Diversity: a Matter of Cell Fate

Glia. Jul, 2003  |  Pubmed ID: 12761864

Early in development of the central nervous system, radial glial cells arise from the neuroepithelial cells lining the ventricles around the time that neurons begin to appear. The transition of neuroepithelial cells to radial glia is accompanied by a series of structural and functional changes, including the appearance of "glial" features, as well as the appearance of new signaling molecules and junctional proteins. However, not all radial glia are alike. Radial glial lineages appear to be heterogeneous both within and across different brain regions. Subtypes of neurogenic radial glia within the cortex, for example, may have restricted potential in terms of the cell types they are able to generate. Radial glia located in different brain regions also differ in their expression of growth factors, a diverse number of transcription factors, and the cell types they generate, suggesting that they are involved in regionalization of the developing nervous system in several aspects. These findings highlight the important but complex role of radial glia as participants in key steps of brain development.

Changing Concepts of Cortical Development

Cerebral Cortex (New York, N.Y. : 1991). Jun, 2003  |  Pubmed ID: 12764026

Neurogenic Radial Glial Cells in Reptile, Rodent and Human: from Mitosis to Migration

Cerebral Cortex (New York, N.Y. : 1991). Jun, 2003  |  Pubmed ID: 12764028

Radial glial cells play at least two crucial roles in cortical development: neuronal production in the ventricular zone (VZ) and the subsequent guidance of neuronal migration. There is evidence that radial glia-like cells are present not only during development but in the adult mammalian brain as well. In addition, radial glial cells appear to be neurogenic in the central nervous system of a number of vertebrate species. We demonstrate here that most dividing progenitor cells in the embryonic human VZ express radial glial proteins. Furthermore, we provide evidence that radial glial cells maintain a vimentin-positive radial fiber throughout each stage of cell division. Asymmetric inheritance of this fiber may be an important factor in determining how neuronal progeny will migrate into the developing cortical plate. Although radial glial cells have traditionally been characterized by their role in guiding migration, their role as neuronal progenitors may represent their defining characteristic throughout the vertebrate CNS.

Terpene Trilactones from Ginkgo Biloba Are Antagonists of Cortical Glycine and GABA(A) Receptors

The Journal of Biological Chemistry. Dec, 2003  |  Pubmed ID: 14504293

Glycine and gamma-aminobutyric acid, type A (GABA(A)) receptors are members of the ligand-gated ion channel superfamily that mediate inhibitory synaptic transmission in the adult central nervous system. During development, the activation of these receptors leads to membrane depolarization. Ligands for the two receptors have important implications both in disease therapy and as pharmacological tools. Terpene trilactones (ginkgolides and bilobalide) are unique constituents of Ginkgo biloba extracts that have various effects on the central nervous system. We have investigated the relative potency of these compounds on glycine and GABA(A) receptors. We find that most of the ginkgolides are selective and potent antagonists of the glycine receptor. Bilobalide, the single major component in G. biloba extracts, also reduces glycine-induced currents, although to a lesser extent. Both ginkgolides and bilobalide inhibit GABA(A) receptors, with bilobalide demonstrating a more potent effect. Additionally, we provide evidence that open channels are required for glycine receptor inhibition by ginkgolides. Finally, we employ molecular modeling to elucidate the similarities and differences in the structure of the terpene trilactones to account for the pharmacological properties of these compounds and demonstrate a striking similarity between ginkgolides and picrotoxinin, a GABA(A) and recombinant glycine alpha-homomeric receptor antagonist.

Cortical Neurons Arise in Symmetric and Asymmetric Division Zones and Migrate Through Specific Phases

Nature Neuroscience. Feb, 2004  |  Pubmed ID: 14703572

Precise patterns of cell division and migration are crucial to transform the neuroepithelium of the embryonic forebrain into the adult cerebral cortex. Using time-lapse imaging of clonal cells in rat cortex over several generations, we show here that neurons are generated in two proliferative zones by distinct patterns of division. Neurons arise directly from radial glial cells in the ventricular zone (VZ) and indirectly from intermediate progenitor cells in the subventricular zone (SVZ). Furthermore, newborn neurons do not migrate directly to the cortex; instead, most exhibit four distinct phases of migration, including a phase of retrograde movement toward the ventricle before migration to the cortical plate. These findings provide a comprehensive and new view of the dynamics of cortical neurogenesis and migration.

Patterns of Neuronal Migration in the Embryonic Cortex

Trends in Neurosciences. Jul, 2004  |  Pubmed ID: 15219738

Real-time imaging of migrating neurons has changed our understanding of how newborn neurons reach their final positions in the developing cerebral cortex. The migratory routes and modes of migration are more diverse and complex than previously thought. The finding that cortical interneurons migrate to the cortex from origins in the ventral telencephalon has already markedly altered our view of cortical migration. More recent findings have demonstrated additional nuances in the migratory pattern and highlighted differences between subsets of interneurons. Moreover, radial migration of pyramidal neurons does not progress smoothly from ventricle to cortical plate, but is instead characterized by distinct migratory phases in which neurons change shape and direction of movement. Integrating these findings with the molecular machinery underlying migration will provide a more complete picture of how the cerebral cortex is assembled.

Controlling Neuron Number: Does Numb Do the Math?

Nature Neuroscience. Aug, 2004  |  Pubmed ID: 15280888

Calcium Waves Propagate Through Radial Glial Cells and Modulate Proliferation in the Developing Neocortex

Neuron. Sep, 2004  |  Pubmed ID: 15339647

The majority of neurons in the adult neocortex are produced embryonically during a brief but intense period of neuronal proliferation. The radial glial cell, a transient embryonic cell type known for its crucial role in neuronal migration, has recently been shown to function as a neuronal progenitor cell and appears to produce most cortical pyramidal neurons. Radial glial cell modulation could thus affect neuron production, neuronal migration, and overall cortical architecture; however, signaling mechanisms among radial glia have not been studied directly. We demonstrate here that calcium waves propagate through radial glial cells in the proliferative cortical ventricular zone (VZ). Radial glial calcium waves occur spontaneously and require connexin hemichannels, P2Y1 ATP receptors, and intracellular IP3-mediated calcium release. Furthermore, we show that wave disruption decreases VZ proliferation during the peak of embryonic neurogenesis. Taken together, these results demonstrate a radial glial signaling mechanism that may regulate cortical neuronal production.

Cortical Development: New Concepts

Neuron. May, 2005  |  Pubmed ID: 15882631

GABA Puts the Brake on Stem Cells

Nature Neuroscience. Sep, 2005  |  Pubmed ID: 16127444

LIS1 RNA Interference Blocks Neural Stem Cell Division, Morphogenesis, and Motility at Multiple Stages

The Journal of Cell Biology. Sep, 2005  |  Pubmed ID: 16144905

Mutations in the human LIS1 gene cause the smooth brain disease classical lissencephaly. To understand the underlying mechanisms, we conducted in situ live cell imaging analysis of LIS1 function throughout the entire radial migration pathway. In utero electroporation of LIS1 small interference RNA and short hairpin dominant negative LIS1 and dynactin cDNAs caused a dramatic accumulation of multipolar progenitor cells within the subventricular zone of embryonic rat brains. This effect resulted from a complete failure in progression from the multipolar to the migratory bipolar state, as revealed by time-lapse analysis of brain slices. Surprisingly, interkinetic nuclear oscillations in the radial glial progenitors were also abolished, as were cell divisions at the ventricular surface. Those few bipolar cells that reached the intermediate zone also exhibited a complete block in somal translocation, although, remarkably, process extension persisted. Finally, axonal growth also ceased. These results identify multiple distinct and novel roles for LIS1 in nucleokinesis and process dynamics and suggest that nuclear position controls neural progenitor cell division.

Constructing Circuits: Neurogenesis and Migration in the Developing Neocortex

Epilepsia. 2005  |  Pubmed ID: 16201991

Our knowledge of the proliferation, migration, and differentiation of neurons has changed dramatically over the last 10 years. Whereas traditionally it was thought that glial and neuronal cells were separate cell lines with different lineages, we now know that this is not true. Radial glia are a type of neural stem cell that generate excitatory pyramidal neurons directly through asymmetric cell division in the ventricular zone (VZ) of the telencephalon and indirectly through the symmetric division of daughter intermediate precursor cells that divide in the subventricular zone (SVZ). Moreover, pyramidal neurons, once thought to migrate only along radial guide fibers to the developing layers of the cortex, have been shown to proceed through four distinct stages of migration during which they change shape, direction, and speed. Gamma-aminobutyric acid (GABAergic) inhibitory interneurons, on the other hand, are generated not in the cortex, but in the medial ganglionic eminence and migrate tangentially to their final cortical destinations. Evidence suggests that GABA activation may play a role in coordinating the generation and migration of both pyramidal and interneuron populations. At the end of neurogenesis, radial glial cells translocate to the cortex and transform into astrocytes. Although they do not actively divide in the adult brain, astrocytes may retain the potential to generate new neurons. These new findings have increased our understanding of the mechanisms underlying certain developmental disorders and, in doing so, reveal potentially useful modes of therapeutic intervention.

A New Era in the Ethics of Human Embryonic Stem Cell Research

Stem Cells (Dayton, Ohio). Nov-Dec, 2005  |  Pubmed ID: 16293581

Scientific progress in human embryonic stem cell (hESC) research and increased funding make it imperative to look ahead to the ethical issues generated by the expected use of hESCs for transplantation. Several issues should be addressed now, even though phase I clinical trials of hESC transplantation are still in the future. To minimize the risk of hESC transplantation, donors of materials used to derive hESC lines will need to be recontacted to update their medical history and screening. Because of privacy concerns, such recontact needs to be discussed and agreed to at the time of donation, before new hESC lines are derived. Informed consent for phase I clinical trials of hESC transplantation also raises ethical concerns. In previous phase I trials of highly innovative interventions, allegations that trial participants had not really understood the risk and benefits caused delays in subsequent trials. Thus, researchers should consider what information needs to be discussed during the consent process for hESC clinical trials and how to verify that participants have a realistic understanding of the study. Lack of attention to the special ethical concerns raised by clinical trials of hESC transplantation and their implications for the derivation of new hESC lines may undermine or delay progress toward stem cell therapies.

The Temporal and Spatial Origins of Cortical Interneurons Predict Their Physiological Subtype

Neuron. Nov, 2005  |  Pubmed ID: 16301176

Interneurons of the cerebral cortex represent a heterogeneous population of cells with important roles in network function. At present, little is known about how these neurons are specified in the developing telencephalon. To explore whether this diversity is established in the early progenitor populations, we conducted in utero fate-mapping of the mouse medial and caudal ganglionic eminences (MGE and CGE, respectively), from which most cortical interneurons arise. Mature interneuron subtypes were assessed by electrophysiological and immunological analysis, as well as by morphological reconstruction. At E13.5, the MGE gives rise to fast-spiking (FS) interneurons, whereas the CGE generates predominantly regular-spiking interneurons (RSNP). Later at E15.5, the CGE produces RSNP classes distinct from those generated from the E13.5 CGE. Thus, we provide evidence that the spatial and temporal origin of interneuron precursors in the developing telencephalic eminences predicts the intrinsic physiological properties of mature interneurons.

Progress in Corticogenesis

Cerebral Cortex (New York, N.Y. : 1991). Jul, 2006  |  Pubmed ID: 16766695

The Role of Intermediate Progenitor Cells in the Evolutionary Expansion of the Cerebral Cortex

Cerebral Cortex (New York, N.Y. : 1991). Jul, 2006  |  Pubmed ID: 16766701

The vertebrate cerebral cortex varies from the 3-layered dorsal cortex of reptiles to the 6-layered lissencephalic cortex characteristic of rodents and to the 6-layered gyrencephalic cortex typical of carnivores and primates. Distinct developmental mechanisms may have evolved independently to account for the radial expansion that produced the multilayered cortex of mammals and for the tangential expansion of cortical surface area that resulted in gyrencephalic cortex. Recent evidence shows that during the late stages of cortical development, radial glial cells divide asymmetrically in the ventricular zone to generate radial glial cells and intermediate progenitor (IP) cells and that IP cells subsequently divide symmetrically in the subventricular zone to produce multiple neurons. We propose that the evolution of this two-step pattern of neurogenesis played an important role in the amplification of cell numbers underlying the radial and tangential expansion of the cerebral cortex.

Patterns of Neural Stem and Progenitor Cell Division May Underlie Evolutionary Cortical Expansion

Nature Reviews. Neuroscience. Nov, 2006  |  Pubmed ID: 17033683

The dramatic evolutionary expansion of the cerebral cortex of Homo sapiens underlies our unique higher cortical functions, and therefore bears on the ultimate issue of what makes us human. Recent insights into developmental events during early proliferative stages of cortical development indicate how neural stem and progenitor cells might interact to produce cortical expansion during development, and could shed light on evolutionary changes in cortical structure.

Estradiol Stimulates Progenitor Cell Division in the Ventricular and Subventricular Zones of the Embryonic Neocortex

The European Journal of Neuroscience. Dec, 2006  |  Pubmed ID: 17229096

Two distinct populations of cerebral cortical progenitor cells that generate neurons during embryogenesis have been identified: radial glial cells and intermediate progenitor cells. Despite advances in our understanding of progenitor cell populations, we know relatively little about factors that regulate their proliferative behaviour. 17-beta-Estradiol (E2) is present in the adult and developing mammalian brain, and plays an important role in central nervous system processes such as neuronal differentiation, survival and plasticity. E2 also stimulates neurogenesis in the adult dentate gyrus. We examined the role of E2 during embryonic cortical neurogenesis through immunohistochemistry, in situ hybridization, functional enzyme assay, organotypic culture and in utero administration of estradiol-blocking agents in mice. We show that aromatase, the E2 synthesizing enzyme, is present in the embryonic neocortex, that estrogen receptor-alpha is present in progenitor cells during cortical neurogenesis, that in vitro E2 administration rapidly promotes proliferation, and that in utero blockade of estrogen receptors decreases proliferation of embryonic cortical progenitor cells. Furthermore, the E2 inhibitor alpha-fetoprotein is expressed at high levels by radial glial cells but at lower levels by intermediate progenitor cells, suggesting that E2 differentially influences the proliferation of these cortical progenitor cell types. These findings demonstrate a new functional role for E2 as a proliferative agent during critical stages of cerebral cortex development.

Blind Patch Clamp Recordings in Embryonic and Adult Mammalian Brain Slices

Nature Protocols. 2006  |  Pubmed ID: 17406279

To obtain electrophysiological recordings in brain slices, sophisticated and expensive pieces of equipment can be used. However, costly microscope equipment with infrared differential interference contrast optics is not always necessary or even desirable. For instance, obtaining a randomized unbiased sample in a given preparation would be better accomplished if cells were not directly visualized before recording. In addition, some preparations require thick slices, and direct visualization is not possible. Here we describe a protocol for the 'blind patch clamp method' that we developed several years ago to perform electrophysiological recordings in mammalian brain slices using a standard patch clamp amplifier, dissecting microscope and recording chamber. Overall, it takes approximately 3-4 h to set up this procedure.

Contribution of Intermediate Progenitor Cells to Cortical Histogenesis

Archives of Neurology. May, 2007  |  Pubmed ID: 17502462

The mammalian cerebral cortex is the most cellularly complex structure in the animal kingdom. Almost all cortical neurons are produced during a limited embryonic period by cortical progenitor cells in a proliferative region that surrounds the ventricular system of the developing brain. The proliferative region comprises 2 distinct zones, the ventricular zone, which is a neuroepithelial layer directly adjacent to the ventricular lumen, and the subventricular zone, which is positioned superficial to the ventricular zone. Recent advances in molecular and cell biology have made possible the study of specific cell populations, and 2 cortical progenitor cell types, radial glial cells in the ventricular zone and intermediate progenitor cells in the subventricular zone, have been shown to generate neurons in the embryonic cerebral cortex. These findings have refined our understanding of cortical neurogenesis, with implications for understanding the causes of neurodevelopmental disorders and for their potential treatment.

Gap Junction Adhesion is Necessary for Radial Migration in the Neocortex

Nature. Aug, 2007  |  Pubmed ID: 17713529

Radial glia, the neuronal stem cells of the embryonic cerebral cortex, reside deep within the developing brain and extend radial fibres to the pial surface, along which embryonic neurons migrate to reach the cortical plate. Here we show that the gap junction subunits connexin 26 (Cx26) and connexin 43 (Cx43) are expressed at the contact points between radial fibres and migrating neurons, and acute downregulation of Cx26 or Cx43 impairs the migration of neurons to the cortical plate. Unexpectedly, gap junctions do not mediate neuronal migration by acting in the classical manner to provide an aqueous channel for cell-cell communication. Instead, gap junctions provide dynamic adhesive contacts that interact with the internal cytoskeleton to enable leading process stabilization along radial fibres as well as the subsequent translocation of the nucleus. These results indicate that gap junction adhesions are necessary for glial-guided neuronal migration, raising the possibility that the adhesive properties of gap junctions may have an important role in other physiological processes and diseases associated with gap junction function.

Neural Stem and Progenitor Cells in Cortical Development

Novartis Foundation Symposium. 2007  |  Pubmed ID: 18494252

Recent work has begun to identify neural stem and progenitor cells in the embryonic and adult brain, and is unravelling the mechanisms whereby new nerve cells are created and delivered to their correct locations. Radial glial (RG) cells, which are present in the developing mammalian brain, have been proposed to be neural stem cells because they produce multiple cell types. Furthermore, time-lapse imaging demonstrates that RG cells undergo asymmetric self-renewing divisions to produce immature neurons that migrate along their parent radial fibre to reach the developing cerebral cortex. RG cells also produce intermediate progenitor (IP) cells that undergo symmetric division in the subventricular zone of the embryonic cortex to produce pairs of neurons. The symmetric IP divisions increase cell number within the same cortical layer. This two-step process of neurogenesis suggests new mechanisms for the generation of cell diversity and cell number in the developing cortex and supports a model similar to that proposed for the development of the fruit fly CNS. In this model, a temporal sequence of gene expression changes in asymmetrically dividing self-renewed RG cells could lead to the differential inheritance of cell identity genes in cortical cells generated at different cell cycles.

GABA Regulates Excitatory Synapse Formation in the Neocortex Via NMDA Receptor Activation

The Journal of Neuroscience : the Official Journal of the Society for Neuroscience. May, 2008  |  Pubmed ID: 18495889

The development of a balance between excitatory and inhibitory synapses is a critical process in the generation and maturation of functional circuits. Accumulating evidence suggests that neuronal activity plays an important role in achieving such a balance in the developing cortex, but the mechanism that regulates this process is unknown. During development, GABA, the primary inhibitory neurotransmitter in adults, excites neurons as a result of high expression of the Na(+)-K(+)-2Cl(-) cotransporter (NKCC1). Using NKCC1 RNA interference knockdown in vivo, we show that GABA-induced depolarization is necessary for proper excitatory synapse formation and dendritic development of newborn cortical neurons. Blocking NKCC1 with the diuretic bumetanide during development leads to similar persistent changes in cortical circuitry in the adult. Interestingly, expression of a voltage-independent NMDA receptor rescues the failure of NKCC1 knockdown neurons to develop excitatory AMPA transmission, indicating that GABA depolarization cooperates with NMDA receptor activation to regulate excitatory synapse formation. Our study identifies an essential role for GABA in the synaptic integration of newborn cortical neurons and suggests an activity-dependent mechanism for achieving the balance between excitation and inhibition in the developing cortex.

Progenitors from the Postnatal Forebrain Subventricular Zone Differentiate into Cerebellar-like Interneurons and Cerebellar-specific Astrocytes Upon Transplantation

Molecular and Cellular Neurosciences. Nov, 2008  |  Pubmed ID: 18718868

Forebrain subventricular zone (SVZ) progenitor cells give rise to glia and olfactory bulb interneurons during early postnatal life in rats. We investigated the potential of SVZ cells to alter their fate by transplanting them into a heterotypic neurogenic and gliogenic environment-the cerebellum. Transplanted cells were examined 1 to 7 weeks and 6 months post transplantation. Forebrain progenitors populated the cerebellum and differentiated into oligodendrocytes, cerebellar-specific Bergmann glia and velate astrocytes, and neurons. The transplanted cells that differentiated into neurons maintained an interneuronal fate: they were GABA-positive, expressed interneuronal markers, such as calretinin, and exhibited membrane properties that are characteristic of interneurons. However, the transplanted interneurons lost the expression of the olfactory bulb transcription factors Tbr2 and Dlx1, and acquired a cerebellar-like morphology. Forebrain SVZ progenitors thus have the potential to adapt to a new environment and integrate into diverse regions, and may be a useful tool in transplantation strategies.

A Time and a Place for Nkx2-1 in Interneuron Specification and Migration

Neuron. Sep, 2008  |  Pubmed ID: 18786351

The homeobox transcription factor, Nkx2-1, plays multiple roles during forebrain development. Using restricted genetic ablation of Nkx2-1, in this issue of Neuron, Butt et al. show that Nkx2-1 in telencephalic progenitors regulates interneuron subtype specification, while Nóbrega-Pereira et al. demonstrate that postmitotic Nkx2-1 regulates migration and sorting of interneurons to the striatum or cortex by controlling the expression of the guidance receptor, Neuropilin-2.

Clinical Trials in Stem Cell Transplantation: Guidelines for Scientific and Ethical Review

Clinical Trials (London, England). 2008  |  Pubmed ID: 18827044

Transplantation of cells derived through the manipulation of pluripotent stem cells may involve great uncertainty and the possibility of serious risks.

GABA Regulates Stem Cell Proliferation Before Nervous System Formation

Epilepsy Currents / American Epilepsy Society. Sep-Oct, 2008  |  Pubmed ID: 18852839

Distinct Behaviors of Neural Stem and Progenitor Cells Underlie Cortical Neurogenesis

The Journal of Comparative Neurology. May, 2008  |  Pubmed ID: 18288691

Neocortical precursor cells undergo symmetric and asymmetric divisions while producing large numbers of diverse cortical cell types. In Drosophila, cleavage plane orientation dictates the inheritance of fate-determinants and the symmetry of newborn daughter cells during neuroblast cell divisions. One model for predicting daughter cell fate in the mammalian neocortex is also based on cleavage plane orientation. Precursor cell divisions with a cleavage plane orientation that is perpendicular with respect to the ventricular surface (vertical) are predicted to be symmetric, while divisions with a cleavage plane orientation that is parallel to the surface (horizontal) are predicted to be asymmetric neurogenic divisions. However, analysis of cleavage plane orientation at the ventricle suggests that the number of predicted neurogenic divisions might be insufficient to produce large amounts of cortical neurons. To understand factors that correlate with the symmetry of cell divisions, we examined rat neocortical precursor cells in situ through real-time imaging, marker analysis, and electrophysiological recordings. We find that cleavage plane orientation is more closely associated with precursor cell type than with daughter cell fate, as commonly thought. Radial glia cells in the VZ primarily divide with a vertical orientation throughout cortical development and undergo symmetric or asymmetric self-renewing divisions depending on the stage of development. In contrast, most intermediate progenitor cells divide in the subventricular zone with a horizontal orientation and produce symmetric daughter cells. We propose a model for predicting daughter cell fate that considers precursor cell type, stage of development, and the planar segregation of fate determinants.

Gap Junctions: Multifaceted Regulators of Embryonic Cortical Development

Trends in Neurosciences. May, 2008  |  Pubmed ID: 18403031

The morphological development of the cerebral cortex from a primitive neuroepithelium into a complex laminar structure underlying higher cognition must rely on a network of intercellular signaling. Gap junctions are widely expressed during embryonic development and provide a means of cell-cell contact and communication. We review the roles of gap junctions in regulating the proliferation of neural progenitors as well as the migration and differentiation of young neurons in the embryonic cerebral cortex. There is substantial evidence that although gap junctions act in the classical manner coupling neural progenitors, they also act as hemichannels mediating the spread of calcium waves across progenitor cell populations and as adhesive molecules aiding neuronal migration. Gap junctions are thus emerging as multifaceted regulators of cortical development playing diverse roles in intercellular communication.

Manipulating Midbrain Stem Cell Self-renewal

Cell Stem Cell. May, 2008  |  Pubmed ID: 18462687

In this issue of Cell Stem Cell, Falk and colleagues (Falk et al., 2008) demonstrate that differential responsiveness to TGF-beta signaling selectively modulates self-renewal of dorsal midbrain stem cells. This observation may lead to strategies for expanding specific neural stem cell subtypes.

Defining the Role of GABA in Cortical Development

The Journal of Physiology. May, 2009  |  Pubmed ID: 19153158

Of the many signals in the developing nervous system, GABA (gamma-aminobutyric acid) has been shown to be one of the earliest neurotransmitters present. Unlike in the adult, where this transmitter acts synaptically to inhibit neurons, during development, GABA can depolarize progenitor cells and their progeny due to their high intracellular chloride concentration. This early form of GABA signalling may provide the main excitatory drive for the immature cortical network and play a central role in regulating cortical development. Many features of GABA signalling are conserved in different species and are recapitulated during neurogenesis in the adult brain, demonstrating the importance of this versatile molecule in driving cortical formation. Here, we present recent evidence supporting the multiple functions of GABA during embryonic development and adult neurogenesis, from regulating progenitor proliferation to influencing the migration and maturation of newborn neurons.

Importing Human Pluripotent Stem Cell Lines Derived at Another Institution: Tailoring Review to Ethical Concerns

Cell Stem Cell. Feb, 2009  |  Pubmed ID: 19200800

Stem cell researchers commonly use human pluripotent stem cell lines derived by other investigators. Researchers may use lines derived elsewhere, provided that their derivation met consensus core standards. Some types of derivation raise heightened levels of ethical concern and require greater scrutiny. To maintain public trust, research institutions need to justify why they allow researchers to use lines whose derivation would not have been permitted locally.

Commentary: the Prospect of Cell-based Therapy for Epilepsy

Neurotherapeutics : the Journal of the American Society for Experimental NeuroTherapeutics. Apr, 2009  |  Pubmed ID: 19332322

About 30% of patient with epilepsy do not respond to available antiepileptic drugs. In addition to seizure suppression, novel approaches are needed to prevent or alleviate epileptogenic process after various types of brain injuries. The use of cell transplants as factories to produce endogeneous anticonvulsants or as bricks to repair abnormal ictogenic and epileptogenic neuronal circuits has generated hope that cell-based therapies could become a novel therapeutic category in the treatment arsenal of epilepsy. Herein we summarize the current status and future perspectives of cell-based therapies in the treatment of epilepsy.

A Stem Cell Niche for Intermediate Progenitor Cells of the Embryonic Cortex

Cerebral Cortex (New York, N.Y. : 1991). Jul, 2009  |  Pubmed ID: 19346271

The excitatory neurons of the mammalian cerebral cortex arise from asymmetric divisions of radial glial cells in the ventricular zone and symmetric division of intermediate progenitor cells (IPCs) in the subventricular zone (SVZ) of the embryonic cortex. Little is known about the microenvironment in which IPCs divide or whether a stem cell niche exists in the SVZ of the embryonic cortex. Recent evidence suggests that vasculature may provide a niche for adult stem cells but its role in development is less clear. We have investigated the vasculature in the embryonic cortex during neurogenesis and find that IPCs are spatially and temporally associated with blood vessels during cortical development. Intermediate progenitors mimic the pattern of capillaries suggesting patterns of angiogenesis and neurogenesis are coordinated during development. More importantly, we find that IPCs divide near blood vessel branch points suggesting that cerebral vasculature establishes a stem cell niche for intermediate progenitors in the SVZ. These data provide novel evidence for the presence of a neurogenic niche for intermediate progenitors in the embryonic SVZ and suggest blood vessels are important for proper patterning of neurogenesis.

The Glial Nature of Embryonic and Adult Neural Stem Cells

Annual Review of Neuroscience. 2009  |  Pubmed ID: 19555289

Glial cells were long considered end products of neural differentiation, specialized supportive cells with an origin very different from that of neurons. New studies have shown that some glial cells--radial glia (RG) in development and specific subpopulations of astrocytes in adult mammals--function as primary progenitors or neural stem cells (NSCs). This is a fundamental departure from classical views separating neuronal and glial lineages early in development. Direct visualization of the behavior of NSCs and lineage-tracing studies reveal how neuronal lineages emerge. In development and in the adult brain, many neurons and glial cells are not the direct progeny of NSCs, but instead originate from transit amplifying, or intermediate, progenitor cells (IPCs). Within NSCs and IPCs, genetic programs unfold for generating the extraordinary diversity of cell types in the central nervous system. The timing in development and location of NSCs, a property tightly linked to their neuroepithelial origin, appear to be the key determinants of the types of neurons generated. Identification of NSCs and IPCs is critical to understand brain development and adult neurogenesis and to develop new strategies for brain repair.

Mammalian Par3 Regulates Progenitor Cell Asymmetric Division Via Notch Signaling in the Developing Neocortex

Neuron. Jul, 2009  |  Pubmed ID: 19640478

Asymmetric cell division of radial glial progenitors produces neurons while allowing self-renewal; however, little is known about the mechanism that generates asymmetry in daughter cell fate specification. Here, we found that mammalian partition defective protein 3 (mPar3), a key cell polarity determinant, exhibits dynamic distribution in radial glial progenitors. While it is enriched at the lateral membrane domain in the ventricular endfeet during interphase, mPar3 becomes dispersed and shows asymmetric localization as cell cycle progresses. Either removal or ectopic expression of mPar3 prevents radial glial progenitors from dividing asymmetrically yet generates different outcomes in daughter cell fate specification. Furthermore, the expression level of mPar3 affects Notch signaling, and manipulations of Notch signaling or Numb expression suppress mPar3 regulation of radial glial cell division and daughter cell fate specification. These results reveal a critical molecular pathway underlying asymmetric cell division of radial glial progenitors in the mammalian neocortex.

Cloning Mice and Men: Prohibiting the Use of IPS Cells for Human Reproductive Cloning

Cell Stem Cell. Jan, 2010  |  Pubmed ID: 20085739

The use of iPSCs and tetraploid complementation for human reproductive cloning would raise profound ethical objections. Professional standards and laws that ban human reproductive cloning by somatic cell nuclear transfer should be revised to also forbid it by other methods, such as iPSCs via tetraploid complementation.

Neurogenic Radial Glia in the Outer Subventricular Zone of Human Neocortex

Nature. Mar, 2010  |  Pubmed ID: 20154730

Neurons in the developing rodent cortex are generated from radial glial cells that function as neural stem cells. These epithelial cells line the cerebral ventricles and generate intermediate progenitor cells that migrate into the subventricular zone (SVZ) and proliferate to increase neuronal number. The developing human SVZ has a massively expanded outer region (OSVZ) thought to contribute to cortical size and complexity. However, OSVZ progenitor cell types and their contribution to neurogenesis are not well understood. Here we show that large numbers of radial glia-like cells and intermediate progenitor cells populate the human OSVZ. We find that OSVZ radial glia-like cells have a long basal process but, surprisingly, are non-epithelial as they lack contact with the ventricular surface. Using real-time imaging and clonal analysis, we demonstrate that these cells can undergo proliferative divisions and self-renewing asymmetric divisions to generate neuronal progenitor cells that can proliferate further. We also show that inhibition of Notch signalling in OSVZ progenitor cells induces their neuronal differentiation. The establishment of non-ventricular radial glia-like cells may have been a critical evolutionary advance underlying increased cortical size and complexity in the human brain.

Research Ethics. NIH Guidelines for Stem Cell Research and Gamete Donors

Science (New York, N.Y.). Feb, 2010  |  Pubmed ID: 20167773

Regenerative Medicine: Cell Reprogramming Gets Direct

Nature. Feb, 2010  |  Pubmed ID: 20182502

Embryonic MGE Precursor Cells Grafted into Adult Rat Striatum Integrate and Ameliorate Motor Symptoms in 6-OHDA-lesioned Rats

Cell Stem Cell. Mar, 2010  |  Pubmed ID: 20207227

We investigated a strategy to ameliorate the motor symptoms of rats that received 6-hydroxydopamine (6-OHDA) lesions, a rodent model of Parkinson's disease, through transplantation of embryonic medial ganglionic eminence (MGE) cells into the striatum. During brain development, embryonic MGE cells migrate into the striatum and neocortex where they mature into GABAergic interneurons and play a key role in establishing the balance between excitation and inhibition. Unlike most other embryonic neurons, MGE cells retain the capacity for migration and integration when transplanted into the postnatal and adult brain. We performed MGE cell transplantation into the basal ganglia of control and 6-OHDA-lesioned rats. Transplanted MGE cells survived, differentiated into GABA(+) neurons, integrated into host circuitry, and modified motor behavior in both lesioned and control rats. Our data suggest that MGE cell transplantation into the striatum is a promising approach to investigate the potential benefits of remodeling basal ganglia circuitry in neurodegenerative diseases.

Connexin 43 Mediates the Tangential to Radial Migratory Switch in Ventrally Derived Cortical Interneurons

The Journal of Neuroscience : the Official Journal of the Society for Neuroscience. May, 2010  |  Pubmed ID: 20484649

The adult cerebral cortex is composed of excitatory and inhibitory neurons that arise from progenitor cells in disparate proliferative regions in the developing brain and follow different migratory paths. Excitatory pyramidal neurons originate near the ventricle and migrate radially to their position in the cortical plate along radial glial fibers. On the other hand, inhibitory interneurons arise in the ventral telencephalon and migrate tangentially to enter the developing cortex before migrating radially to reach their correct laminar position. Gap junction adhesion has been shown to play an important mechanistic role in the radial migration of excitatory neurons. We asked whether a similar mechanism governs the tangential or radial migration of inhibitory interneurons. Using short hairpin RNA knockdown of Connexin 43 (Cx43) and Cx26 together with rescue experiments, we found that gap junctions are dispensable for the tangential migration of interneurons, but that Cx43 plays a role in the switch from tangential to radial migration that allows interneurons to enter the cortical plate and find their correct laminar position. Moreover this action is dependent on the adhesive properties and the C terminus of Cx43 but not the Cx43 channel. Thus, the radial phase of interneuron migration resembles that of excitatory neuron migration in terms of dependence on Cx43 adhesion. Furthermore, gap junctions between migrating interneurons and radial processes were observed by electron microscopy. These findings provide mechanistic and structural support for a gap junction-mediated interaction between migrating interneurons and radial glia during the switch from tangential to radial migration.

Kinesin 3 and Cytoplasmic Dynein Mediate Interkinetic Nuclear Migration in Neural Stem Cells

Nature Neuroscience. Dec, 2010  |  Pubmed ID: 21037580

Radial glial progenitor cells exhibit bidirectional cell cycle-dependent nuclear oscillations. The purpose and underlying mechanism of this unusual 'interkinetic nuclear migration' are poorly understood. We investigated the basis for this behavior by live imaging of nuclei, centrosomes and microtubules in embryonic rat brain slices, coupled with the use of RNA interference (RNAi) and the myosin inhibitor blebbistatin. We found that nuclei migrated independent of centrosomes and unidirectionally away from or toward the ventricular surface along microtubules, which were uniformly oriented from the ventricular surface to the pial surface of the brain. RNAi directed against cytoplasmic dynein specifically inhibited nuclear movement toward the apical surface. An RNAi screen of kinesin genes identified Kif1a, a member of the kinesin-3 family, as the motor for basally directed nuclear movement. These observations provide direct evidence that kinesins are involved in nuclear migration and neurogenesis and suggest that a cell cycle-dependent switch between distinct microtubule motors drives interkinetic nuclear migration.

Developmental Genetics of Vertebrate Glial-cell Specification

Nature. Nov, 2010  |  Pubmed ID: 21068830

Oligodendrocytes and astrocytes are macroglial cells of the vertebrate central nervous system. These cells have diverse roles in the maintenance of neurological function. In the embryo, the genetic mechanisms that underlie the specification of macroglial precursors in vivo appear strikingly similar to those that regulate the development of the diverse neuron types. The switch from producing neuronal to glial subtype-specific precursors can be modelled as an interplay between region-restricted components and temporal regulators that determine neurogenic or gliogenic phases of development, contributing to glial diversity. Gaining insight into the developmental genetics of macroglia has great potential to improve our understanding of a variety of neurological disorders in humans.

A New Subtype of Progenitor Cell in the Mouse Embryonic Neocortex

Nature Neuroscience. May, 2011  |  Pubmed ID: 21478886

A hallmark of mammalian brain evolution is cortical expansion, which reflects an increase in the number of cortical neurons established by the progenitor cell subtypes present and the number of their neurogenic divisions. Recent studies have revealed a new class of radial glia-like (oRG) progenitor cells in the human brain, which reside in the outer subventricular zone. Expansion of the subventricular zone and appearance of oRG cells may have been essential evolutionary steps leading from lissencephalic to gyrencephalic neocortex. Here we show that oRG-like progenitor cells are present in the mouse embryonic neocortex. They arise from asymmetric divisions of radial glia and undergo self-renewing asymmetric divisions to generate neurons. Moreover, mouse oRG cells undergo mitotic somal translocation whereby centrosome movement into the basal process during interphase precedes nuclear translocation. Our finding of oRG cells in the developing rodent brain fills a gap in our understanding of neocortical expansion.

Deriving Excitatory Neurons of the Neocortex from Pluripotent Stem Cells

Neuron. May, 2011  |  Pubmed ID: 21609822

The human cerebral cortex is an immensely complex structure that subserves critical functions that can be disrupted in developmental and degenerative disorders. Recent innovations in cellular reprogramming and differentiation techniques have provided new ways to study the cellular components of the cerebral cortex. Here, we discuss approaches to generate specific subtypes of excitatory cortical neurons from pluripotent stem cells. We review spatial and temporal aspects of cortical neuron specification that can guide efforts to produce excitatory neuron subtypes with increased resolution. Finally, we discuss distinguishing features of human cortical development and their translational ramifications for cortical stem cell technologies.

Development and Evolution of the Human Neocortex

Cell. Jul, 2011  |  Pubmed ID: 21729779

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.

Persistent Sonic Hedgehog Signaling in Adult Brain Determines Neural Stem Cell Positional Identity

Neuron. Jul, 2011  |  Pubmed ID: 21791285

Neural stem cells (NSCs) persist in the subventricular zone (SVZ) of the adult brain. Location within this germinal region determines the type of neuronal progeny NSCs generate, but the mechanism of adult NSC positional specification remains unknown. We show that sonic hedgehog (Shh) signaling, resulting in high gli1 levels, occurs in the ventral SVZ and is associated with the genesis of specific neuronal progeny. Shh is selectively produced by a small group of ventral forebrain neurons. Ablation of Shh decreases production of ventrally derived neuron types, while ectopic activation of this pathway in dorsal NSCs respecifies their progeny to deep granule interneurons and calbindin-positive periglomerular cells. These results show that Shh is necessary and sufficient for the specification of adult ventral NSCs.

Orienting Fate: Spatial Regulation of Neurogenic Divisions

Neuron. Oct, 2011  |  Pubmed ID: 22017981

Cleavage plane orientation has been thought to govern the fate of neural stem cell progeny, but supporting evidence in the neocortex has been sparse. A new study by Postiglione et al. in this issue of Neuron shows that mouse Inscuteable-mediated control of cleavage plane orientation regulates the output of neural progenitor cells.

Blocking Early GABA Depolarization with Bumetanide Results in Permanent Alterations in Cortical Circuits and Sensorimotor Gating Deficits

Cerebral Cortex (New York, N.Y. : 1991). Mar, 2011  |  Pubmed ID: 20624842

A high incidence of seizures occurs during the neonatal period when immature networks are hyperexcitable and susceptible to hypersyncrhonous activity. During development, γ-aminobutyric acid (GABA), the primary inhibitory neurotransmitter in adults, typically excites neurons due to high expression of the Na(+)-K(+)-2Cl(-) cotransporter (NKCC1). NKCC1 facilitates seizures because it renders GABA activity excitatory through intracellular Cl(-) accumulation, while blocking NKCC1 with bumetanide suppresses seizures. Bumetanide is currently being tested in clinical trials for treatment of neonatal seizures. By blocking NKCC1 with bumetanide during cortical development, we found a critical period for the development of α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate synapses. Disruption of GABA signaling during this window resulted in permanent decreases in excitatory synaptic transmission and sensorimotor gating deficits, a common feature in schizophrenia. Our study identifies an essential role for GABA-mediated depolarization in regulating the balance between cortical excitation and inhibition during a critical period and suggests a cautionary approach for using bumetanide in treating neonatal seizures.