Identification of two novel glial-restricted cell populations in the embryonic telencephalon arising from unique origins

Subventricular zone stem cell niche injury is associated with intestinal perforation in preterm infants and predicts future motor impairment

Brain injury is highly associated with preterm birth. Complications of prematurity, including spontaneous or necrotizing enterocolitis (NEC)-associated intestinal perforations, are linked to lifelong neurologic impairment, yet the mechanisms are poorly understood. Early diagnosis of preterm brain injuries remains a significant challenge. Here, we identified subventricular zone echogenicity (SVE) on cranial ultrasound in preterm infants following intestinal perforations. The development of SVE was significantly associated with motor impairment at 2 years. SVE was replicated in a neonatal mouse model of intestinal perforation. Examination of the murine echogenic subventricular zone (SVZ) revealed NLRP3-inflammasome assembly in multiciliated FoxJ1+ ependymal cells and a loss of the ependymal border in this postnatal stem cell niche. These data suggest a mechanism of preterm brain injury localized to the SVZ that has not been adequately considered. Ultrasound detection of SVE may serve as an early biomarker for neurodevelopmental impairment after inflammatory disease in preterm infants.

Glial restricted precursor cells in central nervous system disorders: Current applications and future perspectives

The crosstalk between glial cells and neurons represents an exceptional feature for maintaining the normal function of the central nervous system (CNS). Increasing evidence has revealed the importance of glial progenitor cells in adult neurogenesis, reestablishment of cellular pools, neuroregeneration, and axonal (re)myelination. Several types of glial progenitors have been described, as well as their potentialities for recovering the CNS from certain traumas or pathologies. Among these precursors, glial-restricted precursor cells (GRPs) are considered the earliest glial progenitors and exhibit tripotency for both Type I/II astrocytes and oligodendrocytes. GRPs have been derived from embryos and embryonic stem cells in animal models and have maintained their capacity for self-renewal. Despite the relatively limited knowledge regarding the isolation, characterization, and function of these progenitors, GRPs are promising candidates for transplantation therapy and reestablishment/repair of CNS functions in neurodegenerative and neuropsychiatric disorders, as well as in traumatic injuries. Herein, we review the definition, isolation, characterization and potentialities of GRPs as cell-based therapies in different neurological conditions. We briefly discuss the implications of using GRPs in CNS regenerative medicine and their possible application in a clinical setting. MAIN POINTS: GRPs are progenitors present in the CNS with differentiation potential restricted to the glial lineage. These cells have been employed in the treatment of a myriad of neurodegenerative and traumatic pathologies, accompanied by promising results, herein reviewed.

SOX2+ cell population from normal human brain white matter is able to generate mature oligodendrocytes

OBJECTIVES

A number of neurodegenerative diseases progress with a loss of myelin, which makes them candidate diseases for the development of cell-replacement therapies based on mobilisation or isolation of the endogenous neural/glial progenitor cells, in vitro expansion, and further implantation. Cells expressing A2B5 or PDGFRA/CNP have been isolated within the pool of glial progenitor cells in the subcortical white matter of the normal adult human brain, all of which demonstrate glial progenitor features. However, the heterogeneity and differentiation potential of this pool of cells is not yet well established.

METHODS

We used diffusion tensor images, histopathology, and immunostaining analysis to demonstrate normal cytoarchitecture and the absence of abnormalities in human temporal lobe samples from patients with mesial temporal sclerosis. These samples were used to isolate and enrich glial progenitor cells in vitro, and later to detect such cells in vivo.

RESULTS

We have identified a subpopulation of SOX2+ cells, most of them co-localising with OLIG2, in the white matter of the normal adult human brain in vivo. These cells can be isolated and enriched in vitro, where they proliferate and generate immature (O4+) and mature (MBP+) oligodendrocytes and, to a lesser extent, astrocytes (GFAP+).

CONCLUSION

Our results demonstrate the existence of a new glial progenitor cell subpopulation that expresses SOX2 in the white matter of the normal adult human brain. These cells might be of use for tissue regeneration procedures.

Oligodendrocyte/type-2 astrocyte progenitor cells and glial-restricted precursor cells generate different tumor phenotypes in response to the identical oncogenes

Despite the great interest in identifying the cell-of-origin for different cancers, little knowledge exists regarding the extent to which the specific origin of a tumor contributes to its properties. To directly examine this question, we expressed identical oncogenes in two types of glial progenitor cells, glial-restricted precursor (GRP) cells and oligodendrocyte/type-2 astrocyte progenitor cells (O-2A/OPCs), and in astrocytes of the mouse CNS (either directly purified or generated from GRP cells). In vitro, expression of identical oncogenes in these cells generated populations differing in expression of antigens thought to identify tumor initiating cells, generation of 3D aggregates when grown as adherent cultures, and sensitivity to the chemotherapeutic agent BCNU. In vivo, cells differed in their ability to form tumors, in malignancy and even in the type of host-derived cells infiltrating the tumor mass. Moreover, identical genetic modification of these different cells yielded benign infiltrative astrocytomas, malignant astrocytomas, or tumors with characteristics seen in oligodendrogliomas and small-cell astrocytomas, indicating a contribution of cell-of-origin to the characteristic properties expressed by these different tumors. Our studies also revealed unexpected relationships between the cell-of-origin, differentiation, and the order of oncogene acquisition at different developmental stages in enabling neoplastic growth. These studies thus provide multiple novel demonstrations of the importance of the cell-of-origin in respect to the properties of transformed cells derived from them. In addition, the approaches used enable analysis of the role of cell-of-origin in tumor biology in ways that are not accessible by other more widely used approaches.

DNA methylation map of mouse and human brain identifies target genes in Alzheimer's disease

The central nervous system has a pattern of gene expression that is closely regulated with respect to functional and anatomical regions. DNA methylation is a major regulator of transcriptional activity, and aberrations in the distribution of this epigenetic mark may be involved in many neurological disorders, such as Alzheimer’s disease. Herein, we have analysed 12 distinct mouse brain regions according to their CpG 5’-end gene methylation patterns and observed their unique epigenetic landscapes. The DNA methylomes obtained from the cerebral cortex were used to identify aberrant DNA methylation changes that occurred in two mouse models of Alzheimer’s disease. We were able to translate these findings to patients with Alzheimer’s disease, identifying DNA methylation-associated silencing of three targets genes: thromboxane A2 receptor (TBXA2R), sorbin and SH3 domain containing 3 (SORBS3) and spectrin beta 4 (SPTBN4). These hypermethylation targets indicate that the cyclic AMP response element-binding protein (CREB) activation pathway and the axon initial segment could contribute to the disease.

ASYMMETRIC CELL DIVISION: IMPLICATIONS FOR GLIOMA DEVELOPMENT AND TREATMENT

Glioma is a heterogeneous disease process with differential histology and treatment response. It was previously thought that the histological features of glial tumors indicated their cell of origin. However, the discovery of continuous neuro-gliogenesis in the normal adult brain and the identification of brain tumor stem cells within glioma have led to the hypothesis that these brain tumors originate from multipotent neural stem or progenitor cells, which primarily divide asymmetrically during the postnatal period. Asymmetric cell division allows these cell types to concurrently self-renew whilst also producing cells for the differentiation pathway. It has recently been shown that increased symmetrical cell division, favoring the self-renewal pathway, leads to oligodendroglioma formation from oligodendrocyte progenitor cells. In contrast, there is some evidence that asymmetric cell division maintenance in tumor stem-like cells within astrocytoma may lead to acquisition of treatment resistance. Therefore cell division mode in normal brain stem and progenitor cells may play a role in setting tumorigenic potential and the type of tumor formed. Moreover, heterogeneous tumor cell populations and their respective cell division mode may confer differential sensitivity to therapy. This review aims to shed light on the controllers of cell division mode which may be therapeutically targeted to prevent glioma formation and improve treatment response.

Leukemia inhibitory factor is essential for subventricular zone neural stem cell and progenitor homeostasis as revealed by a novel flow cytometric analysis

Stem cells rely on extracellular signals produced by the niche, which dictate their ability to self-renew, expand and differentiate. It is essential to have sensitive and reproducible methods of either quantifying or isolating these stem cells and progenitors to understand their intrinsic properties and how extrinsic signals regulate their development. However, stem cells are difficult to distinguish from multipotential progenitors, which may look and act like them. Here we define a 4-color flow cytometry panel using CD133, LeX, CD140a, NG2 to define a neural stem cell (NSC) as well as 4 classes of multipotential progenitors and 3 classes of bipotential progenitors, several of which have not been described previously. We performed gain and loss of function studies for leukemia inhibitory factor (LIF) and showed a depletion of NSCs, a subset of multipotential neural precursors and immature oligodendrocytes in LIF null mice. Gain of function studies showed that LIF increased the abundance of these precursors. Our studies also show that these NPs have differential requirements for LIF and ciliary neurotrophic factor (CNTF) and for epidermal growth factor (EGF), fibroblast growth factor (FGF-2) and platelet-derived growth factor (PDGF) for their propagation in vitro. Surprisingly, the related cytokine, CNTF, was less potent than LIF in increasing the NSCs and more potent than LIF in increasing the PDGF responsive multipotential precursors. Finally, we show that LIF increases the expression of the core transcription factors: Klf4, Fbx15, Nanog, Sox2 and c-Myc. Altogether our FACS (fluorescence-activated cell sorter) analyses reveal that the neonatal subventricular zone is far more heterogeneous than previously suspected and our studies provide new insights into the signals and mechanisms that regulate their self-renewal and proliferation.

Derivation of glial restricted precursors from E13 mice

This is a protocol for derivation of glial restricted precursor (GRP) cells from the spinal cord of E13 mouse fetuses. These cells are early precursors within the oligodendrocytic cell lineage. Recently, these cells have been studied as potential source for restorative therapies in white matter diseases. Periventricular leukomalacia (PVL) is the leading cause of non-genetic white matter disease in childhood and affects up to 50% of extremely premature infants. The data suggest a heightened susceptibility of the developing brain to hypoxia-ischemia, oxidative stress and excitotoxicity that selectively targets nascent white matter. Glial restricted precursors (GRP), oligodendrocyte progenitor cells (OPC) and immature oligodendrocytes (preOL) seem to be key players in the development of PVL and are the subject of continuing studies. Furthermore, previous studies have identified a subset of CNS tissue that has increased susceptibility to glutamate excitotoxicity as well as a developmental pattern to this susceptibility. Our laboratory is currently investigating the role of oligodendrocyte progenitors in PVL and use cells at the GRP stage of development. We utilize these derived GRP cells in several experimental paradigms to test their response to select stresses consistent with PVL. GRP cells can be manipulated in vitro into OPCs and preOL for transplantation experiments with mouse PVL models and in vitro models of PVL-like insults including hypoxia-ischemia. By using cultured cells and in vitro studies there would be reduced variability between experiments which facilitates interpretation of the data. Cultured cells also allows for enrichment of the GRP population while minimizing the impact of contaminating cells of non-GRP phenotype.

The genetic signature of perineuronal oligodendrocytes reveals their unique phenotype

Oligodendrocytes--best known for assembling central nervous system myelin--can be categorized as precursors, myelin-forming cells and non-myelinating perineuronal cells. Perineuronal oligodendrocytes have been well characterized morphologically and ultrastructurally, but knowledge about their function remains scanty. It has been proposed that perineuronal oligodendrocytes support neurons and, following injury, transform into myelin-synthesizing cells. Recent findings implicating perineuronal oligodendrocytes in cytoarchitectural abnormalities in the prefrontal cortex of schizophrenia and other psychiatric disorders shed new light on these cells. We have obtained the genetic signature of perineuronal oligodendrocytes by identifying gene expression differences between oligodendrocyte subpopulations using cell-specific tags, microarray technology, quantitative time-resolved polymerase chain reaction and bioinformatics tools. We show that perineuronal cells are the progeny of oligodendrocyte progenitors and, hence, are members of the oligodendrocyte lineage. Physiologically they exhibit a novel phenotype. Their expression of PDGFR-αβ and its growth factor ligand PDGF-CC sets them apart from members of their lineage as this receptor precludes their response to the same growth factors that act on myelinating cells. Their coordinate expression and context-specific usage of transcription factors Olig2, Ascl1 and Pax6, together with the prominent presence of transcription factors Pea3, Lhx2 and Otx2--not hitherto linked to the oligodendrocyte lineage--suggested a cell with features that blur the boundary between a neuron and a glial cell. But they also maintain a reservoir of untranslated transcripts encoding major myelin proteins presumably for a demyelinating episode. This first molecular characterization of perineuronal oligodendrocytes revealed the striking difference between the myelinating and non-myelinating phenotypes.

Precursor cell biology and the development of astrocyte transplantation therapies: lessons from spinal cord injury

This review summarizes current progress on development of astrocyte transplantation therapies for repair of the damaged central nervous system. Replacement of neurons in the injured or diseased central nervous system is currently one of the most popular therapeutic goals, but if neuronal replacement is attempted in the absence of appropriate supporting cells (astrocytes and oligodendrocytes), then the chances of restoring neurological functional are greatly reduced. Although the past 20 years have offered great progress on oligodendrocyte replacement therapies, astrocyte transplantation therapies have been both less explored and comparatively less successful. We have now developed successful astrocyte transplantation therapies by pre-differentiating glial restricted precursor (GRP) cells into a specific population of GRP cell-derived astrocytes (GDAs) by exposing the GRP cells to bone morphogenetic protein-4 (BMP) prior to transplantation. When transplanted into transected rat spinal cord, rat and human GDAs(BMP) promote extensive axonal regeneration, rescue neuronal cell survival, realign tissue structure, and restore behavior to pre-injury levels on a grid-walk analysis of volitional foot placement. Such benefits are not provided by GRP cells themselves, demonstrating that the lesion environment does not direct differentiation in a manner optimally beneficial for the restoration of function. Such benefits also are not provided by transplantation of a different population of astrocytes generated from GRP cells exposed to ciliary neurotrophic factor (GDAs(CNTF)), thus providing the first transplantation-based evidence of functional heterogeneity in astrocyte populations. Moreover, lessons learned from the study of rat cells are strongly predictive of outcomes using human cells. Thus, these studies provide successful strategies for the use of astrocyte transplantation therapies for restoration of function following spinal cord injury.

Cerebral cortex demyelination and oligodendrocyte precursor response to experimental autoimmune encephalomyelitis

Experimentally induced autoimmune encephalomyelitis (EAE) in mice provides an animal model that shares many features with human demyelinating diseases such as multiple sclerosis (MS). To what extent the cerebral cortex is affected by the process of demyelination and how the corollary response of the oligodendrocyte lineage is explicated are still not completely known aspects of EAE. By performing a detailed in situ analysis of expression of myelin and oligodendrocyte markers we have identified areas of subpial demyelination in the cerebral cortex of animals with conventionally induced EAE conditions. On EAE-affected cerebral cortices, the distribution and relative abundance of cells of the oligodendrocyte lineage were assessed and compared with control mouse brains. The analysis demonstrated that A2B5(+) glial restricted progenitors (GRPs) and NG2(+)/PDGFR-α(+) oligodendrocyte precursor cells (OPCs) were increased in number during "early" disease, 20 days post MOG immunization, whereas in the "late" disease, 39 days post-immunization, they were strongly diminished, and there was an accompanying reduction in NG2(+)/O4(+) pre-oligodendrocytes and GST-π mature oligodendrocytes. These results, together with the observed steady-state amount of NG2(-)/O4(+) pre-myelinating oligodendrocytes, suggested that oligodendroglial precursors attempted to compensate for the progressive loss of myelin, although these cells appeared to fail to complete the last step of their differentiation program. Our findings confirm that this chronic model of EAE reproduces the features of neocortex pathology in progressive MS and suggest that, despite the proliferative response of the oligodendroglial precursors, the failure to accomplish final differentiation may be a key contributing factor to the impaired remyelination that characterizes these demyelinating conditions.

Structurally distinct LewisX glycans distinguish subpopulations of neural stem/progenitor cells

There is increasing evidence that the stem and progenitor cell population that builds the central nervous system is very heterogeneous. Stem cell markers with the potential to divide this cell pool into subpopulations with distinct characteristics are sparse. We were looking for new cell type-specific antigens to further subdivide the progenitor pool. Here, we introduce the novel monoclonal antibody clone 5750. We show that it specifically labels cell surfaces of neural stem and progenitor cells. When 5750-expressing cells were isolated by fluorescence-activated cell sorting from embryonic mouse brains, the sorted population showed increased neurosphere forming capacity and multipotency. Neurospheres generated from 5750-positive cells could self-renew and remained multipotent even after prolonged passaging. Carbohydrate binding assays revealed that the 5750 antibody specifically binds to LewisX-related carbohydrates. Interestingly, we found that the LewisX epitope recognized by clone 5750 differs from those detected by other anti-LewisX antibody clones like 487(LeX), SSEA-1(LeX), and MMA(LeX). Our data further reveal that individual anti-LewisX clones can be successfully used to label and deplete different subpopulations of neural cells in vivo and in vitro. In conclusion, we present a new tool for the isolation and characterization of neural subpopulations and provide insights into the complexity of cell surface glycosylation.

Hes1 functions downstream of growth factors to maintain oligodendrocyte lineage cells in the early progenitor stage

Expansion of the progenitor pool of oligodendrocytes (OLs) is a critical process for obtaining appropriate amounts of mature myelin-forming OLs in the developing and regenerating central nervous system. In vitro, fibroblast growth factor-2 (FGF2), together with platelet-derived growth factor (PDGF), is required to expand oligodendrocyte progenitor cells (OLPs) in an unlimited manner, maintaining them in the early progenitor stage. However, the intracellular mechanisms that prevent OLP maturation remain elusive. In order to investigate these mechanisms, we established a mouse OLP primary culture, which enabled us to undertake biochemical analyses. We found that the suppressive effects on maturation of early OLP to the late O4(+) progenitor by PDGF+FGF2 treatment was abrogated by Mek inhibitor, while transfecting cells with a constitutively active Mek1 construct prevented OLP maturation, suggesting that the Mek-Erk pathway is implicated in the effects of the growth factor treatment. The activation of Mek-Erk pathway promoted proliferation of OLP suggesting that cell cycle progression has suppressive effects to the maturation of OLP. Furthermore, molecular screening using DNA microarrays revealed that Hes1, a negative regulator of bHLH transcription factors, is one of the downstream molecules induced by PDGF+FGF2 treatment. We confirmed that forced activation of Mek-Erk pathway is sufficient to induce Hes1 expression and that Hes1, in turn, exerts suppressive effects on the maturation of OL lineage by itself. Our observations thus indicate that Mek-Erk pathway plays pivotal role in preventing early OLP maturation to late OLPs and the effect is mediated by cell cycle progression as well as Hes1 induction.

There is more to a lipid than just being a fat: sphingolipid-guided differentiation of oligodendroglial lineage from embryonic stem cells

Dr. Robert K. Yu's research showed for the first time that the composition of glycosphingolipids is tightly regulated during embryo development. Studies in our group showed that the glycosphingolipid precursor ceramide is also critical for stem cell differentiation and apoptosis. Our new studies suggest that ceramide and its derivative, sphingosine-1-phosphate (S1P), act synergistically on embryonic stem (ES) cell differentiation. When using neural precursor cells (NPCs) derived from ES cells for transplantation, residual pluripotent stem (rPS) cells pose a significant risk of tumor formation after stem cell transplantation. We show here that rPS cells did not express the S1P receptor S1P1, which left them vulnerable to ceramide or ceramide analog (N-oleoyl serinol or S18)-induced apoptosis. In contrast, ES cell-derived NPCs expressed S1P1 and were protected in the presence of S1P or its pro-drug analog FTY720. Consistent with previous studies, FTY720-treated NPCs differentiated predominantly toward oligodendroglial lineage as tested by the expression of the oligodendrocyte precursor cell (OPC) markers Olig2 and O4. As the consequence, a combined administration of S18 and FTY720 to differentiating ES cells eliminated rPS cells and promoted oligodendroglial differentiation. In addition, we show that this combination promoted differentiation of ES cell-derived NPCs toward oligodendroglial lineage in vivo after transplantation into mouse brain.

Emx2 and Foxg1 inhibit gliogenesis and promote neuronogenesis

Neural stem cells (NSCs) give rise to all cell types forming the cortex: neurons, astrocytes, and oligodendrocytes. The transition from the former to the latter ones takes place via lineage-restricted progenitors in a highly regulated way. This process is mastered by large sets of genes, among which some implicated in central nervous system pattern formation. The aim of this study was to disentangle the kinetic and histogenetic roles exerted by two of these genes, Emx2 and Foxg1, in cortico-cerebral precursors. For this purpose, we set up a new integrated in vitro assay design. Embryonic cortical progenitors were transduced with lentiviral vectors driving overexpression of Emx2 and Foxg1 in NSCs and neuronal progenitors. Cells belonging to different neuronogenic and gliogenic compartments were labeled by spectrally distinguishable fluoroproteins driven by cell type-specific promoters and by cell type-specific antibodies and were scored via multiplex cytofluorometry and immunocytofluorescence. A detailed picture of Emx2 and Foxg1 activities in cortico-cerebral histogenesis resulted from this study. Unexpectedly, we found that both genes inhibit gliogenesis and promote neuronogenesis, through distinct mechanisms, and Foxg1 also dramatically stimulates neurite outgrowth. Remarkably, such activities, alone or combined, may be exploited to ameliorate the neuronal output obtainable from neural cultures, for purposes of cell-based brain repair.

Isolation, characterization and preclinical development of human glial-restricted progenitor cells for treatment of neurological disorders

Aim: Glial-restricted progenitor cells (GRPs), a neural cell population that gives rise to astrocytes and oligodendrocytes both in vitro and in vivo, hold great promise as a cellular therapeutic for the treatment of demyelinating and neurodegenerative diseases of the CNS. The manufacturing and characterization protocols of human-derived GRPs (hGRPs; trade name Q-Cells®) for use in a clinical setting that adhere to rigorous standards for their isolation, propagation, characterization and storage are presented. Materials & methods: hGRPs, defined by their immunoreactivity with A2B5 antibodies, were isolated from fetal cadaver forebrain tissue of mice 17–24 weeks gestational age using Miltenyi paramagnetic bead cell separation technology. GRPs were grown in a defined xenobiotic-free medium for 6 days. At harvest, hGRPs were characterized using immunocytochemical techniques. Long-term cryopreservation and storage conditions, and viability upon freeze–thaw were determined. The phenotypic differentiation potential of hGRPs was determined by implantation experiments into the CNS of shiverer mice. Results: hGRPs were isolated from over 50 neural tissues of either sex during gestational ages of 17–24 weeks. Cells expanded out to 6 days in vitro in a xenobiotic-free medium demonstrated very consistent immunocytochemical profiles. No residual antibody used in the purification process was detected after 6 days of growth in vitro. GRPs could be frozen at up to 24 million cells/ml and were over 70% viable upon freeze–thaw. Thawed hGRPs transplanted into the brain of the dysmyelinated shiverer mouse model were observed to differentiate into both glial fibrillary acidic protein-positive astrocytes and myelin basic protein-positive oligodendrocytes; no human-derived NeuN-positive neuronal cells were observed and no abnormal cell proliferation was observed. Conclusion: We demonstrate that hGRPs can be consistently obtained, propagated, cryopreserved and characterized using protocols that can be transferred to a good laboratory practice/good manufacturing practice setting for the manufacture of clinical-grade hGRP cellular therapeutics. Functional data demonstrate that cells manufactured under these conditions are able to differentiate into appropriate cellular phenotypes in an animal model of dysmyelination.

Class III beta-tubulin is constitutively coexpressed with glial fibrillary acidic protein and nestin in midgestational human fetal astrocytes: implications for phenotypic identity

Class III beta-tubulin isotype (betaIII-tubulin) is widely regarded as a neuronal marker in developmental neurobiology and stem cell research. To test the specificity of this marker protein, we determined its expression and distribution in primary cultures of glial fibrillary acidic protein (GFAP)-expressing astrocytes isolated from the cerebral hemispheres of 2 human fetuses at 18 to 20 weeks of gestation. Cells were maintained as monolayer cultures for 1 to 21 days without differentiation induction. By immunofluorescence microscopy, coexpression of betaIII-tubulin and GFAP was detected in cells at all time points but in spatially distinct patterns. The numbers of GFAP+ cells gradually decreased from Days 1 to 21 in vitro, whereas betaIII-tubulin immunoreactivity was present in 100% of cells at all time points. beta-III-tubulin mRNA and protein expression were demonstrated in cultured cells by reverse-transcriptase-polymerase chain reaction and immunoblotting, respectively. Glial fibrillary acidic protein+/beta-III-tubulin-positive cells coexpressed nestin and vimentin but lacked neurofilament proteins, CD133, and glutamate-aspartate transporter. Weak cytoplasmic staining was detected with antibodies against microtubule-associated protein 2 isoforms. Confocal microscopy, performed on autopsy brain samples of human fetuses at 16 to 20 gestational weeks, revealed widespread colocalization of GFAP and betaIII-tubulin in cells of the ventricular/subventricular zones and the cortical plate. Our results indicate that in the midgestational human brain, betaIII-tubulin is not neuron specific because it is constitutively expressed in GFAP+/nestin+ presumptive fetal astrocytes.

Prospective isolation of functionally distinct radial glial subtypes--lineage and transcriptome analysis

Since the discovery of radial glia as the source of neurons, their heterogeneity in regard to neurogenesis has been described by clonal and time-lapse analysis in vitro. However, the molecular determinants specifying neurogenic radial glia differently from radial glia that mostly self-renew remain ill-defined. Here, we isolated two radial glial subsets that co-exist at mid-neurogenesis in the developing cerebral cortex and their immediate progeny. While one subset generates neurons directly, the other is largely non-neurogenic but also gives rise to Tbr2-positive basal precursors, thereby contributing indirectly to neurogenesis. Isolation of these distinct radial glia subtypes allowed determining interesting differences in their transcriptome. These transcriptomes were also strikingly different from the transcriptome of radial glia isolated at the end of neurogenesis. This analysis therefore identifies, for the first time, the lineage origin of basal progenitors and the molecular differences of this lineage in comparison to directly neurogenic and gliogenic radial glia.