Lineage, migration, and fate determination of postnatal subventricular zone cells in the mammalian CNS

Single-Cell RNA-Sequencing in Astrocyte Development, Heterogeneity, and Disease

Astrocytes are the most plentiful cell type in the central nervous system (CNS) and perform complicated functions in health and disease. It is obvious that different astrocyte subpopulations, or activation states, are relevant with specific genomic programs and functions. In recent years, the emergence of new technologies such as single-cell RNA sequencing (scRNA-seq) has made substantial advance in the characterization of astrocyte heterogeneity, astrocyte developmental trajectory, and its role in CNS diseases which has had a significant impact on neuroscience. In this review, we present an overview of astrocyte development, heterogeneity, and its essential role in the physiological and pathological environments of the CNS. We focused on the critical role of single-cell sequencing in revealing astrocyte development, heterogeneity, and its role in different CNS diseases.

Hepatoma Derived Growth Factor Enhances Oligodendrocyte Genesis from Subventricular Zone Precursor Cells

Oligodendrocytes, the myelinating cells of the central nervous system (CNS), perform vital functions in neural protection and communication, as well as cognition. Enhanced production of oligodendrocytes has been identified as a therapeutic approach for neurodegenerative and neurodevelopmental disorders. In the postnatal brain, oligodendrocytes are generated from the neural stem and precursor cells (NPCs) in the subventricular zone (SVZ) and parenchymal oligodendrocyte precursor cells (OPCs). Here, we demonstrate exogenous Hepatoma Derived Growth Factor (HDGF) enhances oligodendrocyte genesis from murine postnatal SVZ NPCs in vitro without affecting neurogenesis or astrogliogenesis. We further show that this is achieved by increasing proliferation of both NPCs and OPCs, as well as OPC differentiation into oligodendrocytes. In vivo results demonstrate that intracerebroventricular infusion of HDGF leads to increased oligodendrocyte genesis from SVZ NPCs, as well as OPC proliferation. Our results demonstrate a novel role for HDGF in regulating SVZ precursor cell proliferation and oligodendrocyte differentiation.

A systematic review of neurogenesis in animal models of early brain damage: Implications for cerebral palsy

Brain damage during early life is the main factor in the development of cerebral palsy (CP), which is one of the leading neurodevelopmental disorders in childhood. Few studies, however, have focused on the mechanisms of cell proliferation, migration, and differentiation in the brain of individuals with CP. We thus conducted a systematic review of preclinical evidence of structural neurogenesis in early brain damage and the underlying mechanisms involved in the pathogenesis of CP. Studies were obtained from Embase, Pubmed, Scopus, and Web of Science. After screening 2329 studies, 29 studies, covering a total of 751 animals, were included. Prenatal models based on oxygen deprivation, inflammatory response and infection, postnatal models based on oxygen deprivation or hypoxic-ischemia, and intraventricular hemorrhage models showed varying neurogenesis responses according to the nature of the brain damage, the time period during which the brain injury occurred, proliferative capacity, pattern of migration, and differentiation profile in neurogenic niches. Results mainly from rodent studies suggest that prenatal brain damage impacts neurogenesis and curbs generation of neural stem cells, while postnatal models show increased proliferation of neural precursor cells, improper migration, and reduced survival of new neurons.

BACE1 Deficiency Causes Abnormal Neuronal Clustering in the Dentate Gyrus

BACE1 is validated as Alzheimer's β-secretase and a therapeutic target for Alzheimer's disease. In examining BACE1-null mice, we discovered that BACE1 deficiency develops abnormal clusters of immature neurons, forming doublecortin-positive neuroblasts, in the developing dentate gyrus, mainly in the subpial zone (SPZ). Such clusters were rarely observed in wild-type SPZ and not reported in other mouse models. To understand their origins and fates, we examined how neuroblasts in BACE1-null SPZ mature and migrate during early postnatal development. We show that such neuroblasts are destined to form Prox1-positive granule cells in the dentate granule cell layer, and mainly mature to form excitatory neurons, but not inhibitory neurons. Mechanistically, higher levels of reelin potentially contribute to abnormal neurogenesis and timely migration in BACE1-null SPZ. Altogether, we demonstrate that BACE1 is a critical regulator in forming the dentate granule cell layer through timely maturation and migration of SPZ neuroblasts.

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BACE1 deficiency causes abnormal neuronal clusters retained in the mouse SPZ

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Mis-migrated neural progenitor cells in the SPZ are destined to form granule cells

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Such neural progenitor cells form excitatory neurons but not inhibitor neurons

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Elevated levels of reelin contribute to abnormal neuronal maturation and migration

Neuronal Progenitor Cells of the Neonatal Subventricular Zone Differentiate and Disperse following Transplantation into the Adult Rat Striatum

We have investigated the suitability of a recently identified and characterized population of neuronal progenitor cells for their potential use in the replacement of degenerating or damaged neurons in the mammalian brain. The unique population of neuronal progenitor cells is situated in a well-delineated region of the anterior part of the neonatal subventricular zone (referred to as SVZa). This region can be separated from the remaining proliferative, gliogenic, subventricular zone encircling the lateral ventricles of the forebrain. Because the neurons arising from the highly enriched neurogenic progenitor cell population of the SVZa ordinarily migrate considerable distances and ultimately express the neurotransmitters GABA and dopamine, we have examined whether they could serve as an alternative source of tissue for neural transplantation. SVZa cells from postnatal day 0-2 rats, prelabeled by intraperitoneal injections of the cell proliferation marker BrdU, were implanted into the striatum of adult rats approximately 1 mo after unilateral denervation by 6-OHDA. To examine the spatio-temporal distribution and phenotype of the transplanted SVZa cells, the experimental recipients were perfused at short (less than 1 wk), intermediate (2-3 wk) and long (5 mo) postimplantation times. The host brains were sectioned and stained with an antibody to BrdU and one of several cell-type specific markers to determine the phenotypic characteristics of the transplanted SVZa cells. To identify neurons we used the neuron-specific antibody TuJ1, or antimembrane-associated protein 2 (MAP-2), and anti-GFAP was used to identify astrocytic glia. At all studied intervals the majority of the surviving SVZa cells exhibited a neuronal phenotype. Moreover, morphologically they could be distinguished from the cells of the host striatum because they resembled the intrinsic granule cells of the olfactory bulb, their usual fate. At longer times, a greater number of the transplanted SVZa cells had migrated from their site of implantation, often towards an outlying blood vessel, and the density of cells within the core of the transplant was reduced. Furthermore, there were rarely signs of transplant rejection or a glial scar surrounding the transplant. In the core of the transplant there were low numbers of GFAP-positive cells, indicating that the transplanted SVZa cells, predominantly TuJ1-positive/MAP2-positive, express a neuronal phenotype. Collectively, the propensity of the SVZa cells to express a neuronal phenotype and to survive and integrate in the striatal environment suggest that they may be useful in the reconstruction of the brain following CNS injury or disease.

Orchestration of Neuronal Differentiation and Progenitor Pool Expansion in the Developing Cortex by SoxC Genes

As the cerebral cortex forms, specialized molecular cascades direct the expansion of progenitor pools, the differentiation of neurons, or the maturation of discrete neuronal subtypes, together ensuring that the correct amounts and classes of neurons are generated. In several neural systems, the SoxC transcriptional regulators, particularly Sox11 and Sox4, have been characterized as functioning exclusively and redundantly in promoting neuronal differentiation. Using the mouse cerebral cortex as a model, Sox11 and Sox4 were examined in the formation of the most complex part of the mammalian brain. Anticipated prodifferentiation roles were observed. Distinct expression patterns and mutant phenotypes, however, reveal that Sox11 and Sox4 are not redundant in the cortex, but rather act in overlapping and discrete populations of neurons. In particular, Sox11 acts in early-born neurons; binding to its partner protein, Neurogenin1, leads to selective targeting and transactivation of a downstream gene, NeuroD1. In addition to neuronal expression, Sox4 was unexpectedly expressed in intermediate progenitor cells, the transit amplifying cell of the cerebral cortex. Sox4 mutant analyses reveal a requirement for Sox4 in IPC specification and maintenance. In intermediate progenitors, Sox4 partners with the proneural gene Neurogenin2 to activate Tbrain2 and then with Tbrain2 to maintain this cell fate. This work reveals an intricately structured molecular architecture for SoxC molecules, with Sox11 acting in a select set of cortical neurons and Sox4 playing an unanticipated role in designating secondary progenitors.

A DEAD-box RNA helicase Ddx54 protein in oligodendrocytes is indispensable for myelination in the central nervous system

We recently reported that a new monoclonal antibody, 4F2, which labels oligodendroglial lineage cells, recognizes a DEAD-box RNA helicase Ddx54 and that Ddx54 binds to myelin basic protein (MBP) in brain and cultured oligodendrocytes. To elucidate the biological function of Ddx54, we generated a recombinant adenovirus, Ad-shRNA:Ddx54, expressing a short hairpin RNA to silence endogenous Ddx54 protein. The virus was intraventricularly injected into the brains of mice on postnatal day (PD) 2. The brains at PD 9 were then analyzed by immunohistochemistry. In untreated normal brain sections, as well as control brains that had been injected with Ad-β-Gal, myelination of axons occurred in the corpus callosum with filamentous patterns of immunosignals of myelin-associated glycoprotein (MAG) and MBP. In Ad-shRNA:Ddx54-injected brain, substantial amounts of MAG and MBP immunosignals were present, but MBP immunosignals accumulated in the subplate layer and did not intrude into the emerging white matter. Immunoblot analysis revealed that Ddx54 knockdown caused a significant decrease in the level of 21.5 kDa MBP isoform and Ddx54, but the amount of Olig2; 2',3'-cyclic nucleotide 3' phosphodiesterase; MAG; three MBP isoforms (14, 17.5, and 18 kDa); and QKI-5, QKI-6, and QKI-7 proteins remained unchanged. Transfection of the Ddx54 expression vector into luciferase reporter-introduced neuroepithelial cells resulted in upregulated MBP promoter activity. Immunoprecipitation of Ddx54 protein in MBP-transfected HEK293 cells indicated that Ddx54 may directly interact with MBP mRNA. These results suggest that Ddx54 protein play an important role in central nervous system myelination, presumably in myelin sheath formation after the differentiation of oligodendrocytes.

Laminin regulates postnatal oligodendrocyte production by promoting oligodendrocyte progenitor survival in the subventricular zone

The laminin family of extracellular matrix proteins are expressed broadly during embryonic brain development, but are enriched at ventricular and pial surfaces where laminins mediate radial glial attachment during corticogenesis. In the adult brain, however, laminin distribution is restricted, yet is found within the vascular basal lamina and associated fractones of the ventricular zone (VZ)-subventricular zone (SVZ) stem cell niche, where laminins regulate adult neural progenitor cell proliferation. It remains unknown, however, if laminins regulate the wave of oligodendrogenesis that occurs in the neonatal/early postnatal VZ-SVZ. Here we report that Lama2, the gene that encodes the laminin α2-subunit, regulates postnatal oligodendrogenesis. At birth, Lama2-/- mice had significantly higher levels of dying oligodendrocyte progenitor cells (OPCs) in the OPC germinal zone of the dorsal SVZ. This translated into fewer OPCs, both in the dorsal SVZ well as in an adjacent developing white matter tract, the corpus callosum. In addition, intermediate progenitor cells that give rise to OPCs in the Lama2-/- VZ-SVZ were mislocalized and proliferated nearer to the ventricle surface. Later, delays in oligodendrocyte maturation (with accompanying OPC accumulation), were observed in the Lama2-/- corpus callosum, leading to dysmyelination by postnatal day 21. Together these data suggest that prosurvival laminin interactions in the developing postnatal VZ-SVZ germinal zone regulate the ability, or timing, of oligodendrocyte production to occur appropriately.

Heterogeneity of astrocytic form and function

Astrocytes participate in all essential CNS functions, including blood flow regulation, energy metabolism, ion and water homeostasis, immune defence, neurotransmission, and adult neurogenesis. It is thus not surprising that astrocytic morphology and function differ between regions, and that different subclasses of astrocytes exist within the same brain region. Recent lines of work also show that the complexity of protoplasmic astrocytes increases during evolution. Human astrocytes are structurally more complex, larger, and propagate calcium signals significantly faster than rodent astrocytes. In this chapter, we review the diversity of astrocytic form and function, while considering the markedly expanded roles of astrocytes with phylogenetic evolution. We also define major challenges for the future, which include determining how astrocytic functions are locally specified, defining the molecular controls upon astrocytic fate and physiology and establishing how evolutionary changes in astrocytes contribute to higher cognitive functions.

Neural stem/progenitor cells transplanted to the hypoglossal nucleus integrates with the host CNS in adult rats and promotes motor neuron survival

Transplantation of neural stem cells and the mobilization of endogenous neuronal precursors in the adult brain have been proposed as therapeutic strategies for central nervous system disorders and injuries. The aim of the present study was to investigate the possible survival and integration of grafted neural progenitor cells (NPCs) from the subventricular zone (SVZ) in a hypoglossal nerve avulsion model with substantial neuronal loss. Adult neural progenitor cells (NPCs) from the subventricular zone (SVZ) were cultured from inbred transgenic eGFP Lewis rats and transplanted to the hypoglossal nucleus of inbred Lewis rat from the same family but that were not carrying the eGFP strain after avulsion of the hypoglossal nerve. Grafted cells survived in the host more than 3 months and differentiated into neurons [βIII tubulin (Tuj-1 staining)] with fine axon- and dendrite-like processes as well as astrocytes (GFAP) and oligodendrocytes (O4) with typical morphology. Staining for synaptic structures (synaptophysin and bassoon) indicated integration of differentiated cells from the graft with the host CNS. Furthermore, transplantation of NPCs increased the number of surviving motoneurons in the hypoglossal nucleus after nerve avulsion that, if untreated, result in substantial neuronal death. The NPCs used in this study expressed VEGF in vitro as well as in vivo following transplantation that may mediate the rescue effect of the axotomized motoneurons.

Induction of striatal neurogenesis and generation of region-specific functional mature neurons after ischemia by growth factors

Object

The capacity to replace lost neurons after insults is retained by several regions of adult mammalian brains. However, it is unknown how many neurons actually replace and mature into region-specific functional neurons to restore lost brain function. In this paper, the authors asked whether neuronal regeneration could be achieved efficaciously by growth factor treatment using a global ischemia model in rats, and they analyzed neuronal long-term maturation processes.

Methods

Rat global ischemia using a modified 4-vessel occlusion model was used to induce consistent ischemic neuronal injury in the dorsolateral striatum. To potentiate the proliferative response of neural progenitors, epidermal growth factor and fibroblast growth factor–2 were infused intraventricularly for 7 days from Day 2 after ischemia. Six weeks after ischemia, the number of neurons was counted in the defined dorsolateral striatum. To label the proliferating neural progenitors for tracing studies, 5-bromo-2′-deoxyuridine (BrdU; 150 mg/kg, twice a day) was injected intraperitoneally from Days 5 to 7, and immunohistochemical studies were conducted to explore the maturation of these progenitors. Migration of the progenitors was further studied by enhanced green fluorescent protein retrovirus injection. The effect of an antimitotic drug (cytosine arabinoside) on the neuronal count was also evaluated for contribution to regeneration. To see electrophysiological changes, treated rats were subjected to slice studies by whole-cell recordings. Finally, the effect of neural regeneration was assessed by motor performance by using the staircase test.

Results

Following epidermal growth factor and fibroblast growth factor–2 infusion into the lateral ventricles for 7 days beginning on Day 2, when severe neuronal loss in the adult striatum was confirmed (2.3% of normal controls), a significant increase of striatal neurons was observed at 6 weeks (~ 15% of normal controls) compared with vehicle controls (~ 5% of normal controls). Immunohistochemical studies by BrdU and enhanced green fluorescent protein retrovirus injection disclosed proliferation of neural progenitors in the subventricular zone and their migration to the ischemic striatum. By BrdU tracing study, NeuN- and BrdU-positive new neurons significantly increased at 6 and 12 weeks following the treatment. These accounted for 4.6 and 11.0% of the total neurons present, respectively. Antimitotic treatment demonstrated an approximately 66% reduction in neurons at 6 weeks. Further long-term studies showed dynamic changes of site-specific maturation among various neuronal subtypes even after 6 weeks. Electrophysiological properties of these newly appeared neurons underwent changes that conform to neonatal development. These regenerative changes were accompanied by a functional improvement of overall behavioral performance.

Conclusions

Treatment by growth factors significantly contributed to regeneration of mature striatal neurons after ischemia by endogenous neural progenitors, which was accompanied by electrophysiological maturation and improved motor performance. Recognition and improved understanding of these underlying dynamic processes will contribute to the development of novel and efficient regenerative therapies for brain injuries.

Ischemia induced neural stem cell proliferation and differentiation in neonatal rat involved vascular endothelial growth factor and transforming growth factor-beta pathways

Brain ischemia is a leading cause of mortality and morbidity in premature infants. Knowing the fate of neural stem cells in the subventricular zone (SVZ) after ischemia and the mechanisms that determine this fate would be useful in manipulating neural stem cell proliferation and differentiation and possibly in reversing ischemic damage. We sought to identify the genes involved in the proliferation and differentiation of neural stem cells after exposure to ischemia in a 3-day-old rat model that approximates ischemia in premature infants. Proliferating cells were labeled by bromodeoxyuridine (BrdU) through intraperitoneal injection. Using immunfluorescence assays, we observed the proliferation and differentiation of neural stem cells. Genes were identified with GeneChip and real-time quantitative polymerase chain reaction analysis. Ischemic rats had more BrdU-positive cells in the SVZ at all four time points and more neural stem cells differentiation into neurons, astrocytes, and oligodendrocytes. GeneChip analysis showed a 3- to 10-fold increase in the mRNA expression of vascular endothelial growth factor, transforming growth factor-beta, and their receptors in the SVZ. PCR assays and Western blot analyses confirmed these results, indicating that vascular endothelial growth factor and transforming growth factor-beta might be two of the factors that involve post-ischemic neural stem cell proliferation and differentiation.

Erythropoietin attenuates brain injury, subventricular zone expansion, and sensorimotor deficits in hypoxic-ischemic neonatal rats

The aim of this study was to investigate the effect of erythropoietin (EPO) on histological brain injury, subventricular zone (SVZ) expansion, and sensorimotor function deficits induced by hypoxia-ischemia (HI) in newborn rat pups. Seven-day-old male rat pups were divided into six groups: normoxia control, normoxia EPO, hypoxia control, hypoxia EPO, HI control, and HI EPO group. Sham surgery or HI was performed in all animals. HI was induced by ligation of the right common carotid artery followed by 90 min of hypoxia with 8% oxygen. Recombinant human EPO 3 U/g or saline was administered intraperitoneally, immediately, at 24- and 48-hr after insult. At two weeks after insult, animals were challenged with cylinder-rearing test for evaluating forelimb asymmetry to determine sensorimotor function. All animals were then sacrificed for volumetric analysis of the cerebral hemispheres and the SVZ. The saline-treated HI rats showed marked asymmetry by preferential use of the non-impaired, ipsilateral paw in the cylinder-rearing test. Volumetric analysis of brains revealed significantly decreased preserved ipsilateral hemispheric volume and increased ipsilateral SVZ volume compared with the sham-operated animals. Treatment of EPO significantly improved forelimb asymmetry and preserved ipsilateral hemispheric volume along with decreased expansion of ipsilateral SVZ following HI compared to the saline-treated HI rats. These results support the use of EPO as a candidate drug for treatment of neonatal hypoxic-ischemic brain damage.

Validating in utero electroporation for the rapid analysis of gene regulatory elements in the murine telencephalon

With the ultimate goal of understanding how genetic modules have evolved in the telencephalon, we set out to modernize the functional analysis of cross-species cis-regulatory elements in mouse. In utero electroporation is rapidly replacing transgenesis as the method of choice for gain- and loss-of-function studies in the murine telencephalon, but the application of this technique to the analysis of transcriptional regulation has yet to be fully explored and exploited. To empirically define the developmental stages required to target specific populations of neurons in the dorsal telencephalon, or pallium, which gives rise to the neocortex in mouse, we performed a temporal and spatial analysis of the migratory properties of electroporated versus birth-dated cells. Next, we compared the activities of two known Ngn2 enhancers via transgenesis and in utero electroporation, demonstrating that the latter technique more faithfully reports the endogenous telencephalic expression pattern observed in an Ngn2lacZ knock-in line. Finally, we used this approach to test the telencephalic activities of a series of deletion constructs comprised of the zebrafish ER81 upstream regulatory region, allowing us to identify a previously uncharacterized enhancer that displays cross-species activity in the murine piriform cortex and lateral neocortex, yet not in more medial domains of the forebrain. Taken together, our data supports the contention that in utero technology can be exploited to rapidly examine the architecture and evolution of pallial-specific cis-regulatory elements.

Systemically delivered Erythropoietin transiently enhances adult hippocampal neurogenesis

Erythropoietin is a primary regulator of erythropoiesis in the hematopoietic system. More recently erythropoietin has been shown to play a role in neurogenesis and provide neurotrophic support to injured CNS tissue. Here the effects of large systemic doses of erythropoietin on basal levels of adult hippocampal neurogenesis in mice were examined. A 7-day period of recombinant human erythropoietin (rhEPO) administration increased the number of bromodeoxyuridine [BrdU(+)] cells in the sub-granular zone (SGZ) by 30%. Analysis of cell phenotype revealed an increase in mitotically active doublecortin(+) neuronal progenitor cells and glial fibrillary acidic protein(+) SGZ radial astrocytes/stem cells but not mature S100beta(+) astrocytes. These effects appeared to be mediated, in part, by mitogen-activated protein kinase signaling and potentially regulated by suppressor of cytokine signaling-3. Hippocampal levels of phosphorylated extracellular signal-related kinase 42/44 and suppressor of cytokine signaling-3 were increased 2-6 h after a single systemic rhEPO injection. However, rhEPO had no observed effect on the long-term survival of new born cells in the SGZ, with similar numbers of BrdU(+) cells and BrdU(+)/NeuN(+) co-labeled cells after 4 weeks. Therefore, systemically delivered rhEPO transiently increased adult hippocampal neurogenesis without any apparent long-term effects.

Different networks, common growth factors: shared growth factors and receptors of the vascular and the nervous system

Growth factors and their respective receptors are key regulators during development and for homeostasis of the nervous system. In addition, changes in growth factor function, availability or downstream signaling is involved in many neuropathological disorders like Parkinson's disease, Alzheimer's disease, amyotrophic lateral sclerosis, stroke and brain tumours. Research of the recent years revealed that some growth factors, initially discovered as neural growth factors are also affecting blood vessels [e.g. nerve growth factor (NGF) or brain-derived neurotrophic factor (BDNF)]. Likewise, vascular growth factors, such as vascular endothelial growth factor (VEGF), which was previously described as an endothelial cell specific mitogen, also affect neural cells. The discovery of shared growth factors affecting the vascular and the nervous system is of relevance for potential therapies of vascular and neurological diseases. This review aims to give an overview about the growing field of common growth factors and receptors within the two different networks.

Adult neurogenesis and cellular brain repair with neural progenitors, precursors and stem cells

Recent work in neuroscience has shown that the adult central nervous system (CNS) contains neural progenitors, precursors and stem cells that are capable of generating new neurons, astrocytes and oligodendrocytes. While challenging the previous dogma that no new neurons are born in the adult mammalian CNS, these findings bring with them the future possibilities for development of novel neural repair strategies. The purpose of this review is to present the current knowledge about constitutively occurring adult mammalian neurogenesis, highlight the critical differences between 'neurogenic' and 'non-neurogenic' regions in the adult brain, and describe the cardinal features of two well-described neurogenic regions-the subventricular zone/olfactory bulb system and the dentate gyrus of the hippocampus. We also provide an overview of presently used models for studying neural precursors in vitro, mention some precursor transplantation models and emphasize that, in this rapidly growing field of neuroscience, one must be cautious with respect to a variety of methodological considerations for studying neural precursor cells both in vitro and in vivo. The possibility of repairing neural circuitry by manipulating neurogenesis is an intriguing one, and, therefore, we also review recent efforts to understand the conditions under which neurogenesis can be induced in non-neurogenic regions of the adult CNS. This work aims towards molecular and cellular manipulation of endogenous neural precursors in situ, without transplantation. We conclude this review with a discussion of what might be the function of newly generated neurons in the adult brain, and provide a summary of present thinking about the consequences of disturbed adult neurogenesis and the reaction of neurogenic regions to disease.

Characterization of thromboxane A2 receptor signaling in developing rat oligodendrocytes: nuclear receptor localization and stimulation of myelin basic protein expression

The present work investigates the role of thromboxane A(2) (TXA(2)) receptors in the development of oligodendrocytes (OLGs). The results demonstrate that the proteins of the TXA(2) signaling pathway, i.e., cyclooxygenase (COX-1), TXA(2) synthase (TS), and TXA(2) receptor (TPR) are expressed in the developing rat brain during myelination. Furthermore, culture of OLG progenitor cells (OPCs) revealed that the expression levels of these proteins as well as TXA(2) synthesis increase during OLG maturation. Separate studies established that activation of TPRs by the agonist U46619 increases intracellular calcium in both OPCs and OLGs as visualized by digital fluorescence imaging. Immunocytochemical staining demonstrated that TPRs are localized in the plasma membrane and perinuclear compartments in OPCs. However, during OLG differentiation, TPRs shift their localization pattern and also become associated with the nuclear compartment. This shift to nuclear localization was confirmed by biochemical analysis in cultured cells and by immunocytochemical analysis in developing rat brain. Finally, it was found that U46619 activation of TPRs in maturing OLGs resulted in enhanced myelin basic protein (MBP) expression. Alternatively, inhibition of endogenous TPR signaling led to reduced MBP expression. Furthermore, TPR-mediated MBP expression was found to be associated with increased transcription from the MBP promoter using a MBP-luciferase reporter. Collectively, these findings suggest a novel TPR signaling pathway in OLGs and a potential role for this signaling during OLG maturation and myelin production.

A novel mode of tangential migration of cortical projection neurons

Projection neurons of the developing cerebral cortex are generated in the cerebral ventricular zone and subsequently move to the developing cortical plate via radial migration. Conversely, most inhibitory interneurons originate in the ganglionic eminences and enter the developing cortical plate by tangential migration. Using immunohistochemical analysis together with tracer labeling experiments in organotypic brain slices, we show that a portion of cortical projection neurons migrates tangentially over long distances. Lineage analysis revealed that these neurons are derived from Emx1+ cortical progenitors and express the transcription factor Satb2 but do not express GABA or Olig1. In vitro and in vivo analysis of reeler mutant brains demonstrated that although reeler mutation does not influence tangential migration of interneurons, it affects the tangential migration of cortical projection neurons.

Influence of EGF/bFGF treatment on proliferation, early neurogenesis and infarct volume after transient focal ischemia

The persistence of neurogenesis in the adult mammalian forebrain suggests that endogenous precursors may be a potential source for neuronal replacement after injury or neurodegeneration. On the other hand basic fibroblast growth factor (bFGF) and epidermal growth factor (EGF) can facilitate neural precursor proliferation in the adult rodent subventricular zone (SVZ) and dentate gyrus. As the application of EGF and bFGF was found to boost neurogenesis after global ischemia, in this study we investigated whether a combined intracerebroventricular (i.c.v.) EGF/bFGF treatment over a period of 2 weeks affects the proliferation of newly generated cells in the endothelin-1 model of transient focal ischemia in adult male Sprague-Dawley rats as well. As assessed by toluidine blue staining, EGF/bFGF substantially increased the infarct volume in ischemic animals. Chronic 5'-bromodeoxyuridine (BrdU) i.c.v. application revealed an EGF/bFGF-induced increase in cell proliferation in the lateral ventricle 14 days after surgery. Proliferation in the striatum increased after ischemia, whereas in the dentate gyrus and in the dorsal 3rd ventricle the number of cells decreased. Analysis of the neuronal fate of these cells by co-staining with a doublecortin (DCX) antibody showed that the growth factors concomitantly nearly doubled early neurogenesis in the ipsilateral striatum in ischemic animals but diminished it in the dentate gyrus. Because of the increased infarct volume and unclear long-term outcome further modifications of a chronic treatment schedule are needed before final conclusions concerning the perspectives of such an approach can be made.

Hypoxic-ischemic injury stimulates subventricular zone proliferation and neurogenesis in the neonatal rat

Neurogenesis persists throughout life in the rodent subventricular zone (SVZ) and increases in the adult after brain injury. In this study, postnatal day 7 (P7) rats underwent right carotid artery ligation followed by 8% O2 exposure for 90 min, a lesioning protocol that resulted in ipsilateral forebrain hypoxic-ischemic (HI) injury. The effects of HI injury on SVZ cell proliferation and neurogenesis were examined 1-3 wk later by morphometric measurement of dorsolateral SVZ size; by immunoassays to detect incorporation of bromodeoxyuridine (BrdU) in proliferating cells; and by immunoassays of doublecortin, a microtubule-associated protein expressed only by immature neurons. For determining the cell phenotypes of newly generated cells, tissue sections were double labeled with antibodies to BrdU and markers of mature neurons (neuronal nuclear protein), astrocytes (glial fibrillary acidic protein), or oligodendroglia (RIP). HI injury resulted in enlargement of the ipsilateral SVZ at P14-28 and a corresponding increase in BrdU cell numbers both in the ipsilateral SVZ and striatum at P21. HI injury also stimulated SVZ neurogenesis, based on increased doublecortin immunostaining in the SVZ ipsilateral to lesioning at P14-28. However, 4 wk after HI injury, in the lesioned striatum, although BrdU/glial fibrillary acidic protein and BrdU/RIP-labeled cells were identified, no BrdU/neuronal nuclear protein double-labeled cells were found. These results suggest that although acute neonatal HI injury stimulates SVZ proliferation and neurogenesis, there is inadequate trophic support for survival of newly generated neurons. Identification of the trophic factors that enhance maturation and survival of immature neurons could provide important clues for improving recovery after neonatal brain injury.

Adult neurogenesis and repair of the adult CNS with neural progenitors, precursors, and stem cells

Recent work in neuroscience has shown that the adult central nervous system contains neural progenitors, precursors, and stem cells that are capable of generating new neurons, astrocytes, and oligodendrocytes. While challenging previous dogma that no new neurons are born in the adult mammalian CNS, these findings bring with them future possibilities for the development of novel neural repair strategies. The purpose of this review is to present current knowledge about constitutively occurring adult mammalian neurogenesis, to highlight the critical differences between "neurogenic" and "non-neurogenic" regions in the adult brain, and to describe the cardinal features of two well-described neurogenic regions-the subventricular zone/olfactory bulb system, and the dentate gyrus of the hippocampus. We also provide an overview of currently used models for studying neural precursors in vitro, mention some precursor transplantation models, and emphasize that, in this rapidly growing field of neuroscience, one must take caution with respect to a variety of methodological considerations for studying neural precursor cells both in vitro and in vivo. The possibility of repairing neural circuitry by manipulating neurogenesis is an intriguing one, and, therefore, we also review recent efforts to understand the conditions under which neurogenesis can be induced in non-neurogenic regions of the adult CNS. This work aims toward molecular and cellular manipulation of endogenous neural precursors in situ, without transplantation. We conclude this review with a discussion of what the function might be of newly generated neurons in the adult brain and provide a summary of current thinking about the consequences of disturbed adult neurogenesis and the reaction of neurogenic regions to disease.

Postnatal neurogenesis and gliogenesis in the olfactory bulb from NG2-expressing progenitors of the subventricular zone

We used a 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP)-enhanced green fluorescent protein (EGFP) transgenic mouse to study postnatal subventricular zone (SVZ) progenitor fate, with a focus on the olfactory bulb (OB). The postnatal OB of the CNP-EGFP mouse contained EGFP+ interneurons and oligodendrocytes. In the anterior SVZ, the majority of EGFP+ progenitors were NG2+. These NG2+/EGFP+ progenitors expressed the OB interneuron marker Er81, the neuroblast markers doublecortin (DC) and Distalless-related homeobox (DLX), or the oligodendrocyte progenitor marker Nkx2.2. In the rostral migratory stream (RMS), EGFP+ cells displayed a migrating phenotype. A fraction of these cells were either NG2-/Er81+/DC+/DLX+ or NG2+/Nkx2.2+. DiI (1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate) injection into the lateral ventricle (LV) of early postnatal mice demonstrated that NG2+/EGFP+ progenitors migrate from the SVZ through the RMS into the OB. Moreover, fluorescence-activated cell-sorting-purified NG2+/CNP-EGFP+ or NG2+/beta-actin-enhanced yellow fluorescent protein-positive (EYFP+) progenitors transplanted into the early postnatal LV displayed extensive rostral and caudal migration. EYFP+ or EGFP+ graft-derived cells within the RMS were DLX+/Er81+ or Nkx2.2+, migrated to the OB, and differentiated to interneurons and oligodendrocytes. In the subcortical white matter (SCWM), grafted cells differentiated to either oligodendrocytes or astrocytes. Transplantation of NG2+/EYFP+ progenitors selectively purified from the SVZ showed that these cells were migratory and generated glia and neurons in the OB, hippocampus, and striatum. In contrast, cortical, OB, or cerebellar NG2+ cells had a very limited migratory potential and gave rise to glia in the SCWM and striatum. Our findings indicate region-specific differences between NG2+ progenitor cells and show that NG2+ cells can migrate throughout the RMS and contribute to both gliogenesis and neurogenesis in the postnatal OB.

Mouse models of childhood cancer of the nervous system

Targeted cancer treatments rely on understanding signalling cascades, genetic changes, and compensatory programmes activated during tumorigenesis. Increasingly, pathologists are required to interpret molecular profiles of tumour specimens to target new treatments. This is challenging because cancer is a heterogeneous disease-tumours change over time in individual patients and genetic lesions leading from preneoplasia to malignancy can differ substantially between patients. For childhood tumours of the nervous system, the challenge is even greater, because tumours arise from progenitor cells in a developmental context different from that of the adult, and the cells of origin, neural progenitor cells, show considerable temporal and spatial heterogeneity during development. Thus, the underlying mechanisms regulating normal development of the nervous system also need to be understood. Many important advances have come from model mouse genetic systems. This review will describe several mouse models of childhood tumours of the nervous system, emphasising how understanding the normal developmental processes, combined with mouse models of cancer and the molecular pathology of the human diseases, can provide the information needed to treat cancer more effectively.

Sonic hedgehog is required for progenitor cell maintenance in telencephalic stem cell niches

To directly test the requirement for hedgehog signaling in the telencephalon from early neurogenesis, we examined conditional null alleles of both the Sonic hedgehog and Smoothened genes. While the removal of Shh signaling in these animals resulted in only minor patterning abnormalities, the number of neural progenitors in both the postnatal subventricular zone and hippocampus was dramatically reduced. In the subventricular zone, this was partially attributable to a marked increase in programmed cell death. Consistent with Hedgehog signaling being required for the maintenance of stem cell niches in the adult brain, progenitors from the subventricular zone of floxed Smo animals formed significantly fewer neurospheres. The loss of hedgehog signaling also resulted in abnormalities in the dentate gyrus and olfactory bulb. Furthermore, stimulation of the hedgehog pathway in the mature brain resulted in elevated proliferation in telencephalic progenitors. These results suggest that hedgehog signaling is required to maintain progenitor cells in the postnatal telencephalon.

Prenatal development of the rodent rostral migratory stream

The aim of this study was to elucidate the embryological origins of the unique neuronal progenitor cells that form the rostral migratory stream (RMS), the path traversed by cells from the anterior part of the forebrain subventricular zone (SVZa) en route to the olfactory bulb. To determine when and where cells constituting the RMS initially exhibit their characteristic neuronal phenotype and high mitotic capacity, we analyzed the cells of the rat forebrain between embryonic day 14 (E14) and postnatal day 2 (P2). At E14, cells with a neuronal phenotype were observed within the ventricular zone in close proximity to the mantle layer of the future olfactory bulb. By E15, cells expressing neuronal markers are also PSA-NCAM immunoreactive and become aligned in chains of similarly oriented cells, a hallmark of the postnatal RMS. The cells that form chains organize into a patch that enlarges in the anterior-posterior and medial-lateral dimensions from E16 to E22 (birth). In comparing the forebrain cytoarchitecture to the pattern of cell type-specific staining, the patch constitutes only the central part of the proximal RMS. Early during development, the region of the RMS surrounding the patch expresses low levels of PSA-NCAM and neuron-specific markers. The proliferative activity of cells forming the patch vs. nonpatch regions of the RMS was analyzed following a short bromodeoxyuridine (BrdU) exposure. Between E15 and E22, the patch can be recognized by the mitotic activity of its cells; the cells of the patch incorporate less BrdU than the nonpatch portion of the RMS. The time course of appearance of cells forming the RMS indicates that the RMS arises in advance and independently of the cortical SVZ. Although the patch and the nonpatch regions of the embryonic RMS appear to merge postnatally, the two regions may originate separately under the influence of distinct intrinsic and extrinsic factors.

Differentiating adult hippocampal stem cells into neural crest derivatives

To investigate the degree of plasticity of hippocampal neural stem cells from adult mice (mHNSC), we have analyzed their differentiation in co-culture with quail neural crest cells. In mixed culture, mHNSC give rise to several non-neuronal neural crest derivatives, including melanocytes, chondrocytes and smooth muscle cells. The data suggest that neural crest cell-derived short-range cues that are recognized across species can instruct adult mHNSC to differentiate into neural crest phenotypes.

Early development of voltage-gated ion currents and firing properties in neurons of the mouse cerebral cortex

Voltage- and current-clamp recordings were made from acute slices of mouse cerebral cortex from embryonic day 14 to postnatal day 17. We targeted cells in the migratory population of the embryonic intermediate zone (IZ) and in deep layers of embryonic and postnatal cortical plate (CP). IZ neurons maintain fairly consistent properties through the embryonic period, all expressing high-input resistance, inward Na(+) currents and outward K(+) currents, and none showing any hyperpolarization-activated currents. In CP neurons, several changes in physiological properties occur in the late embryonic and early postnatal period: inward Na(+) current density is strongly upregulated while outward K(+) current density remains almost unchanged, input resistance drops dramatically, and a hyperpolarization-activated current resembling I(h) appears. As a result of these changes, the action potential becomes larger, shorter in duration, and its threshold shifts to more negative potentials. In addition, CP cells become capable of firing repetitively and an increasing fraction show spontaneous action potentials. This coordinated development of ion channel properties may help to time the occurrence of developmentally relevant spontaneous activity in the immature cortex.

Oligodendrocytes and ischemic brain injury

Oligodendrocytes, myelin-forming glial cells of the central nervous system, are vulnerable to damage in a variety of neurologic diseases. Much is known of primary myelin injury, which occurs in settings of genetic dysmyelination or demyelinating disease. There is growing awareness that oligodendrocytes are also targets of injury in acute ischemia. Recognition of oligodendrocyte damage in animal models of ischemia requires attention to their distinct histologic features or use of specific immunocytochemical markers. Like neurons, oligodendrocytes are highly sensitive to injury by oxidative stress, excitatory amino acids, trophic factor deprivation, and activation of apoptotic pathways. Understanding mechanisms of oligodendrocyte death may suggest new therapeutic strategies to preserve or restore white matter function and structure after ischemic insults.

Control of cell survival and proliferation of postnatal PSA-NCAM(+) progenitors

In the present work, we studied the effects of several growth factors on survival and proliferation of freshly isolated neural progenitors expressing the polysialylated form of neural cell adhesion molecule (PSA-NCAM). Cells were obtained from postnatal day 2 rat forebrain, using isolation method. We found that (1) insulin-like growth factor 1 (IGF-1) exerts a powerful survival effect by inhibiting apoptotic cell death, (2) epidermal growth factor (EGF) strongly increases cell proliferation, (3) the combination of IGF-1 plus EGF promotes cellular expansion, (4) basic fibroblast growth factor displays only a weak mitogenic effect, and (5) platelet-derived growth factor-AA (PDGF-AA) has no effect on cell survival and proliferation. These results suggest that the postnatal PSA-NCAM(+) progenitors characterized in the present work may represent a transitional stage, between the embryonic EGF-responsive neural progenitors and the postnatal PSA-NCAM(+) progenitors already described that are PDGF-responsive. For these "early PSA-NCAM(+) progenitors," insulin-like growth factor 1 and EGF seem to play a pivotal role in the control of cell death and cell proliferation.

In vivo infusions of exogenous growth factors into the fourth ventricle of the adult mouse brain increase the proliferation of neural progenitors around the fourth ventricle and the central canal of the spinal cord

Stem cells isolated from the fourth ventricle and spinal cord form neurospheres in vitro in response to basic fibroblast growth factor (FGF2)+heparin (H) or epidermal growth factor (EGF)+FGF2 together. To determine whether these growth factor conditions are sufficient to induce stem cells within the fourth ventricle and spinal cord to proliferate and expand their progeny in vivo, we infused EGF and FGF2, alone or together, with or without H, into the fourth ventricle for 6 days via osmotic minipumps. Animals were injected with bromodeoxyuridine (BrdU) on days 4, 5 and 6 of infusion in order to label cells proliferating in response to the growth factors. Infusions of EGF+FGF2+H into the fourth ventricle resulted in the largest proliferative effect, a 10.8-fold increase in the number of BrdU+ cells around the fourth ventricle, and a 33.5-fold increase in the number of BrdU+ cells around the central canal of the spinal cord, as compared to vehicle infused controls. The majority of the cells were nestin+ after 6 days of infusion. Seven weeks post-infusion, 22 and 30% of the number of BrdU+ cells induced to proliferate after 6 days of EGF+FGF2+H infusions were still detected around the fourth ventricle and central canal of the spinal cord, respectively. Analysis of the fates of the remaining cells showed that a small percentage of BrdU+ cells around the fourth ventricle and in the white matter of the spinal cord differentiated into astrocytes and oligodendrocytes. BrdU+ neurons were not found in the brainstem or in the grey matter of the cervical spinal cord 7 weeks post-infusion. These results show that endogenous stem cells and progenitors around the fourth ventricle and central canal of the spinal cord proliferate in response to exogenously applied growth factors, but unlike in the lateral ventricle where they generate some new neurons, they only produce new astrocytes and oligodendrocytes at 7 weeks post-infusion.

Treatment of neural injury with marrow stromal cells

We describe our preclinical studies on the use of bone-marrow stromal cells (MSC; an uncharacterised mixed population of plastic-adherent cells) in the treatment of neural injury. These cells obtained from donor rats or human beings have been directly transplanted into brain or administered intra-arterially or intravenously. MSC selectively target injured tissue and promote functional recovery. Signals that target inflammatory cells to injured tissue probably direct MSC to injury sites. Although some MSC express proteins typical of neural cells, the possibility that benefit is derived by replacement of infarcted tissue with differentiated MSC is highly unlikely. MSC activate endogenous restorative responses in injured brain, which include angiogenesis, neurogenesis, and synaptogenesis. Given the robust therapeutic benefit of these cells in the treatment of experimental neural injury, and the fact that MSC have been used in the treatment of other human disease, there is justification for further preclinical studies leading to clinical trials for the treatment of neural injury such as stroke.

Exogenous growth factors induce the production of ganglion cells at the retinal margin

Neural progenitors at the retinal margin of the post-hatch chicken normally produce amacrine and bipolar cells, but not photoreceptor or ganglion cells. The purpose of this study was to test whether exogenous growth factors influence the types of cells produced by progenitors at the retinal margin. We injected insulin, FGF2 or a combination of insulin and FGF2 into the vitreous chamber of post-hatch chickens. To assay for growth factor-induced changes at the retinal margin, we used in situ hybridization and immunocytochemistry on cryosections. One day after the final injection, we found that insulin alone stimulated the addition of cells to the retinal margin, but this was not further increased when FGF2 was applied with insulin. Insulin alone increased the number of cells in the progenitor zone that expressed neurofilament, and this was further increased when FGF2 was applied with insulin. These neurofilament-expressing cells in the progenitor zone included differentiating neurons that expressed Islet1 or Hu. Four days after the final dose of growth factor, we found that the production of ganglion cells was induced by co-injection of insulin and FGF2, but not by either insulin or FGF2 alone. We conclude that the types of cells produced by progenitors at the retinal margin can be altered by exogenous growth factors and that normally the microenvironment imposes limitations on the types of neurons produced.

Identification of neural stem cells in the adult vertebrate brain

Neurogenesis continues into adult life in restricted germinal layers. The identification of the neural stem cells that give rise to these new neurons has important clinical implications and provides fundamental information to understand the origins of the new neurons. Work in adult birds and rodents yielded a surprising result: the neural stem cells appear to have characteristics of glia. In adult birds, the primary neuronal precursors are radial glia. In adult mammals, the primary neuronal precursors have properties of astrocytes. Radial glial cells have previously been shown to transform into astrocytes; both cell types are classically considered part of a committed astroglial lineage. Instead, we propose that neural stem cells are contained within this astroglial lineage. These findings in adult vertebrate brain, together with recent work in the developing mammalian cerebral cortex, force us to reexamine traditional concepts about the origin of neurons and glia in the central nervous system. In particular, neural stem cells possess a surprisingly elaborate structure, suggesting that in addition to their progenitor role, they have important structural and metabolic support functions. The very same cells that give birth to new neurons also seem to nurture their maturation and support their function.

Cell proliferation and differentiation from ependymal, subependymal and choroid plexus cells in response to stroke in rats

We tested the hypothesis that populations of ependymal, subependymal and choroid plexus cells proliferate and differentiate after stroke in adult rats. Rats were subjected to 2 h of middle cerebral artery occlusion (n=70) and euthanized at 1, 2, 4, 7, 14, 21 and 28 days (10 per time point). Hematoxylin and eosin staining and immunostaining were performed using antibodies against bromodeoxyuridine, neuronal nuclear antigen and glial fibrillary acidic protein after stroke. In normal nonischemic rats (n=10), single layers of ependymal and choroid plexus cells do not react with bromodeoxyuridine, neuronal nuclear antigen or glial fibrillary acidic protein. Individual subependymal cells express glial fibrillary acidic protein and bromodeoxyuridine, but not neuronal nuclear antigen. After stroke, increased bromodeoxyuridine reactivity was present in multiple layers of ependymal cells and nodules of subependymal cells and in scattered choroid plexus cells from 2 to 28 days and peaked at 7 days. Bromodeoxyuridine immunoreactivity colocalized with neural phenotypes of neuronal nuclear antigen (approximately 0.1-3.5%) and glial fibrillary acidic protein (approximately 8.6%) immunoreactivity in cells in the ventricular zone and the subventricular zone, as well as in the choroid plexus of the ischemia affected hemisphere. Our data suggest that ependymal, subependymal and choroid plexus cells are potential neural precursor cells in the adult mammalian brain.

Proliferation of progenitor cells in the adult rat brain correlates with the presence of vimentin-expressing astrocytes

It is well established that proliferation of progenitor cells persists within the hippocampal dentate gyrus (DG) and the subventricular zone of the lateral ventricle (SVZ) in the adult brain. The aim of the present study was to determine whether the rate of cell proliferation within these germinative zones could be correlated to the occurrence of a particular glial environment. The cell proliferation marker bromodeoxyuridine (BrdU) was administrated to rats under different physiological and experimental conditions known to modify the rate of progenitor cell proliferation. Within both germinative zones, BrdU-labeled nuclei were associated with cell bodies immunostained for the neuronal marker polysialylated neural cell adhesion molecule, but not for the glial markers glial fibrillary acidic protein (GFAP) or vimentin (VIM). In all the rats examined, however, proliferating (BrdU-labeled) cells always exhibited close relationships with immature-like astrocytes that expressed both GFAP and VIM. There was a dramatic decrease of cell proliferation in the DG from both the aged rats and the corticosterone-treated adult rats that was correlated with a decreased expression of vimentin by the astrocytes present in this region. In contrast, both cell proliferation and vimentin expression were only slightly affected in the SVZ from these two treatment groups. Conversely, after either adrenalectomy or a surgical lesion through the lateral hippocampus, the increase in cell proliferation observed in the DG was correlated to the occurrence of an increased number of GFAP and VIM double immunostained structures in these regions. All together, these data suggest that immature-like astrocytes present in the germinative zones may provide a microenvironment involved in sustaining the proliferation of progenitor cells.

A unified hypothesis on the lineage of neural stem cells

For many years, it was assumed that neurons and glia in the central nervous system were produced from two distinct precursor pools that diverged early during embryonic development. This theory was partially based on the idea that neurogenesis and gliogenesis occurred during different periods of development, and that neurogenesis ceased perinatally. However, there is now abundant evidence that neural stem cells persist in the adult brain and support ongoing neurogenesis in restricted regions of the central nervous system. Surprisingly, these stem cells have the characteristics of fully differentiated glia. Neuroepithelial stem cells in the embryonic neural tube do not show glial characteristics, raising questions about the putative lineage from embryonic to adult stem cells. In the developing brain, radial glia have long been known to produce cortical astrocytes, but recent data indicate that radial glia might also divide asymmetrically to produce cortical neurons. Here we review these new developments and propose that the stem cells in the central nervous system are contained within the neuroepithelial --> radial glia --> astrocyte lineage.

EGF infusion stimulates the proliferation and migration of embryonic progenitor cells transplanted in the adult rat striatum

Immature progenitor cells (generated by in vitro propagation) may provide a useful alternative to primary cells (from dissected embryonic tissue) for transplantation if their migratory and proliferative and differentiation properties can be controlled and directed in vivo. In this study E15 murine EGF-responsive progenitor cells were transplanted to the striatum of adult rats. Simultaneously, these animals received continuous infusion of either epidermal growth factor (EGF) or vehicle, to the lateral ventricle, for 8 days. In animals that received EGF, the transplanted progenitors migrated toward the lateral ventricle and proliferated, as evidenced by bromodeoxyuridine incorporation. Progenitor cells transplanted to rats that received vehicle infusions showed neither of these responses. In all animals, transplanted progenitors expressed an immature astrocyte or oligodendrocyte phenotype, the majority of cells being astrocytes. We conclude that EGF stimulates the migration and proliferation of murine progenitor cells in vivo, either directly or indirectly, but does not influence their phenotypic differentiation.

Prolonged corticosterone treatment of adult rats inhibits the proliferation of oligodendrocyte progenitors present throughout white and gray matter regions of the brain

It is well established that glucocorticoids inhibit the proliferation of progenitor cells that occurs in the hippocampal dentate gyrus of adult mammals. Active cell proliferation also occurs in the subventricular zone (SVZ) of the lateral ventricle and, to a lesser extent, throughout white and gray matter regions of the adult brain. The aim of the present study was to determine whether extrahippocampal cell proliferation is also affected by glucocorticoids. The cell proliferation marker bromodeoxyuridine (BrdU) was administered to control rats, to adrenalectomized rats, and to rats treated with a daily injection of corticosterone (10 mg/kg) for a period of 15 days. In control and adrenalectomized rats, high to low numerical densities of BrdU-labeled nuclei were detected within the different forebrain regions examined. In rats treated with corticosterone, a dramatic decrease of cell proliferation was detected in the dentate gyrus, but also throughout all white and gray matter regions examined, except for the SVZ of the lateral ventricle. Double-labeling experiments indicated that throughout the different white and gray forebrain regions examined, except for the SVZ, BrdU-labeled nuclei were essentially associated with cells immunostained for the marker of oligodendrocyte progenitors NG2. These data indicate that glucocorticoids inhibit the proliferation of oligodendrocyte precursors located throughout the white and gray matter regions of the adult rat brain. Since the proliferation of oligodendrocyte precursors plays a major role in the processes of remyelination, these data raise the question of possible detrimental effects of therapeutic treatments of CNS trauma based on the administration of glucocorticoids.

Morphological bases for a role of nitric oxide in adult neurogenesis

The subventricular zone (SVZ) of the adult mouse brain retains the capacity to generate new neurons from stem cells. The neuronal precursors migrate tangentially along the rostral migratory stream (RMS) towards the olfactory bulb, where they differentiate as periglomerular and granular interneurons. In this study, we have investigated whether nitric oxide (NO), a signaling molecule in the nervous system with a role in embryonic neurogenesis, may be produced in the proximity of the progenitor cells in the adult brain, as a prerequisite to proposing a functional role for NO in adult neurogenesis. Proliferating and immature precursor cells were identified by immunohistochemistry for bromo-deoxyuridine (BrdU) and PSA-NCAM, respectively, and nitrergic neurons by either NADPH-diaphorase staining or immunohistochemical detection of neuronal NO synthase (NOS I). Nitrergic neurons with long varicose processes were found in the SVZ, intermingled with chains of cells expressing PSA-NCAM or containing BrdU. Neurons with similar characteristics surrounded the RMS all along its caudo-rostral extension as far as the core of the olfactory bulb. No expression of NOS I by precursor cells was detected either in the proliferation or in the migration zones. Within the olfactory bulb, many small cells in the granular layer and around the glomeruli expressed either PSA-NCAM or NOS I and, in some cases, both markers. Colocalization was also found in a few isolated cells at a certain distance from the neurogenesis areas. The anatomical disposition shown indicates that NO may be released close enough to the neuronal progenitors to allow a functional influence of this messenger in adult neurogenesis.

Polysialylated neural cell adhesion molecule-positive CNS precursors generate both oligodendrocytes and Schwann cells to remyelinate the CNS after transplantation

Transplantation offers a means of identifying the differentiation and myelination potential of early neural precursors, features relevant to myelin regeneration in demyelinating diseases. In the postnatal rat brain, precursor cells expressing the polysialylated (PSA) form of the neural cell adhesion molecule NCAM have been shown to generate mostly oligodendrocytes and astrocytes in vitro (Ben-Hur et al., 1998). Immunoselected PSA-NCAM+ newborn rat CNS precursors were expanded as clusters with FGF2 and grafted into a focal demyelinating lesion in adult rat spinal cord. We show that these neural precursors can completely remyelinate such CNS lesions. While PSA-NCAM+ precursor clusters contain rare P75+ putative neural crest precursors, they do not generate Schwann cells in vitro even in the presence of glial growth factor. Yet they generate oligodendrocytes, astrocytes, and Schwann cells in vivo when confronted with demyelinated axons in a glia-free area. We confirmed the transplant origin of these Schwann cells using Y chromosome in situ hybridization and immunostaining for the peripheral myelin protein P0 of tissue from female rats that had been grafted with male cell clusters. The number and distribution of Schwann cells within remyelinated tissue, and the absence of P0 mRNAs in donor cells, indicated that Schwann cells were generated by expansion and differentiation of transplanted PSA-NCAM+ neural precursors and were not derived from contaminating Schwann cells. Thus, transplantation into demyelinated CNS tissue reveals an unexpected differentiation potential of a neural precursor, resulting in remyelination of CNS axons by PNS and CNS myelin-forming cells.

Marrow-mindedness: a perspective on neuropoiesis

There are pluripotent stem cells in the adult brain that might not be very different from those found in bone marrow. Recent and profound advances in the field of neuropoiesis, which often rely on insights from studies of hematopoiesis and in some instances use cross-paradigms with this field, have already revealed that bone marrow has much in common with so-called 'brain marrow'. Proliferative primogenitors and developmentally regulated molecules are hallmarks of both neuropoiesis and hematopoiesis. This article will focus on recent advances in neuropoiesis within a central core of the mature brain that is referred to as brain marrow, discussing its pluripotency and proliferative capacity, in vitro and molecular assays used in its study, and markers of neuropoietic stem/progenitor cells. As hematopoiesis research has led to the discovery of numerous morphogenetic factors, it is anticipated that studies of neuropoiesis should also uncover many new factors and genes that affect the growth and differentiation of neural cells. Recent breakthroughs in the stem-cell field prompt an inclusion of rationale for the persistence of normal stem/progenitor cells even in the aged brain. By analogy with hematopoiesis research, a thorough investigation of brain marrow should provide basic insights into developmental and persistent neurogenesis while anticipating cell-transplant and gene therapies for debilitating neurological diseases.

Multipotent stem/progenitor cells with similar properties arise from two neurogenic regions of adult human brain

Recent in vitro studies have shown that the periventricular subependymal zone (SEZ) of the rodent brain is capable of de novo generation of neurons and glia. There is less information available on neurogenesis in the adult human brain, and no study has shown the clonal generation of neurons and glia from in vitro-generated "neurospheres." Here we describe the isolation of proliferative stem/progenitor cells within neurospheres from two different regions, the SEZ and the hippocampus, from surgical biopsy specimens of adult (24-57 years) human brain. Using light and electron microscopy; immunocytochemistry for a variety of neuronal, glial, and developmental (including extracellular matrix; ECM) markers; and the reverse transcriptase polymerase chain reaction to demonstrate different gene transcripts found in neurospheres, it is shown that the adult human brain harbors a complex population of stem/progenitor cells that can generate neuronal and glial progeny under particular in vitro growth conditions. These methods also show that these neurospheres contain both neurons and glia and demonstrate regional similarities at the mRNA level, indicating common stem/progenitor cell types within two different neurogenic regions of the adult human brain. In addition to the synthesis of developmentally regulated molecules such as the ECM protein tenascin-C, a variety of other genes (e.g., Pax 6) and proteins (e.g. , Bcl-2) involved in cell survival and differentiation are expressed by adult human brain neurospheres.

Immunohistochemical localization of erythropoietin and its receptor in the developing human brain

We have previously shown erythropoietin (Epo) and its receptor (Epo-R) to be present in the fetal human central nervous system (CNS), and Epo to be present in the spinal fluid of normal preterm and term infants. To investigate the cellular specificities and developmental patterns of expression of these polypeptides in the human brain-areas that have not been well researched-we designed the following study. Human brains ranging in maturity from 5 weeks post-conception to adult were preserved at the time of elective abortion, surgical removal (tubal pregnancy, or removal for temporal lobe epilepsy), or autopsy. Immunohistochemistry was used to localize Epo and Epo-R reactivity in brains of different stages of development. Astrocytes, neurons, and microglia were identified in sequential tissue sections by specific antibodies. At 5 to 6 weeks post-conception, both Epo and Epo-R localized to cells in the periventricular germinal zone. At 10 weeks post-conception, Epo immunoreactivity was present throughout the cortical wall, with the most intense immunoreactivity present in the ventricular and subventricular zones. Epo-R, in contrast, was localized primarily to the subventricular zone, with little staining evident in the ventricular zone. In late fetal brains, Epo-R reactivity was most prominent in astrocytic cells, although modest reactivity was observed in certain neuron populations. In contrast, Epo staining localized primarily to neurons in fetal brains, although a subpopulation of astrocytes was also immunoreactive. In postnatal brains, both astrocyte and neuron populations were immunoreactive with antibodies to Epo-R and Epo. From these results it is clear that Epo and its receptor are present in the developing human brain as early as 5 weeks post-conception, and each protein shows a specific distribution that changes with development. We speculate that Epo is important in neurodevelopment, and that it also plays a role in brain homeostasis later in life, functioning in an autocrine or paracrine manner.