Basic fibroblast growth factor endows dorsal telencephalic neural progenitors with the ability to differentiate into oligodendrocytes but not gamma-aminobutyric acidergic neurons

The Dorsal Wave of Neocortical Oligodendrogenesis Begins Embryonically and Requires Multiple Sources of Sonic Hedgehog

Neural progenitor cells in the developing dorsal forebrain give rise to excitatory neurons, astrocytes, and oligodendrocytes for the neocortex. While we are starting to gain a better understanding about the mechanisms that direct the formation of neocortical neurons and astrocytes, far less is known about the molecular mechanisms that instruct dorsal forebrain progenitors to make oligodendrocytes. In this study, we show that Sonic hedgehog (Shh) signaling is required in dorsal progenitors for their late embryonic transition to oligodendrogenesis. Using genetic lineage-tracing in mice of both sexes, we demonstrate that most oligodendrocytes in the embryonic neocortex derive from Emx1⁺ dorsal forebrain progenitors. Deletion of the Shh signaling effector Smo specifically in Emx1⁺ progenitors led to significantly decreased oligodendrocyte numbers in the embryonic neocortex. Conversely, knock-out of the Shh antagonist Sufu was sufficient to increase neocortical oligodendrogenesis. Using conditional knock-out strategies, we found that Shh ligand is supplied to dorsal progenitors through multiple sources. Loss of Shh from Dlx5/6⁺ interneurons caused a significant reduction in oligodendrocytes in the embryonic neocortex. This phenotype was identical to that observed upon Shh deletion from the entire CNS using Nestin-Cre, indicating that interneurons migrating into the neocortex from the subpallium are the primary neural source of Shh for dorsal oligodendrogenesis. Additionally, deletion of Shh from migrating interneurons together with the choroid plexus epithelium led to a more severe loss of oligodendrocytes, suggesting that the choroid plexus is an important non-neural source of Shh ligand. Together, our studies demonstrate that the dorsal wave of neocortical oligodendrogenesis occurs earlier than previously appreciated and requires highly regulated Shh signaling from multiple embryonic sources.SIGNIFICANCE STATEMENT Most neocortical oligodendrocytes are made by neural progenitors in the dorsal forebrain, but the mechanisms that specify this fate are poorly understood. This study identifies Sonic hedgehog (Shh) signaling as a critical pathway in the transition from neurogenesis to oligodendrogenesis in dorsal forebrain progenitors during late embryonic development. The timing of this neuron-to-glia "switch" coincides with the arrival of migrating interneurons into the dorsal germinal zone, which we identify as a critical source of Shh ligand, which drives oligodendrogenesis. Our data provide evidence for a new model in which Shh signaling increases in the dorsal forebrain late in embryonic development to provide a temporally regulated mechanism that initiates the third wave of neocortical oligodendrogenesis.

bHLH transcription factors in neural development, disease, and reprogramming

The formation of functional neural circuits in the vertebrate central nervous system (CNS) requires that appropriate numbers of the correct types of neuronal and glial cells are generated in their proper places and times during development. In the embryonic CNS, multipotent progenitor cells first acquire regional identities, and then undergo precisely choreographed temporal identity transitions (i.e. time-dependent changes in their identity) that determine how many neuronal and glial cells of each type they will generate. Transcription factors of the basic-helix-loop-helix (bHLH) family have emerged as key determinants of neural cell fate specification and differentiation, ensuring that appropriate numbers of specific neuronal and glial cell types are produced. Recent studies have further revealed that the functions of these bHLH factors are strictly regulated. Given their essential developmental roles, it is not surprising that bHLH mutations and de-regulated expression are associated with various neurological diseases and cancers. Moreover, the powerful ability of bHLH factors to direct neuronal and glial cell fate specification and differentiation has been exploited in the relatively new field of cellular reprogramming, in which pluripotent stem cells or somatic stem cells are converted to neural lineages, often with a transcription factor-based lineage conversion strategy that includes one or more of the bHLH genes. These concepts are reviewed herein.

FGF signaling controls Shh-dependent oligodendroglial fate specification in the ventral spinal cord

Background

Most oligodendrocytes of the spinal cord originate from ventral progenitor cells of the pMN domain, characterized by expression of the transcription factor Olig2. A minority of oligodendrocytes is also recognized to emerge from dorsal progenitors during fetal development. The prevailing view is that generation of ventral oligodendrocytes depends on Sonic hedgehog (Shh) while dorsal oligodendrocytes develop under the influence of Fibroblast Growth Factors (FGFs).

Results

Using the well-established model of the chicken embryo, we show that ventral spinal progenitor cells activate FGF signaling at the onset of oligodendrocyte precursor cell (OPC) generation. Inhibition of FGF receptors at that time appears sufficient to prevent generation of ventral OPCs, highlighting that, in addition to Shh, FGF signaling is required also for generation of ventral OPCs. We further reveal an unsuspected interplay between Shh and FGF signaling by showing that FGFs serve dual essential functions in ventral OPC specification. FGFs are responsible for timely induction of a secondary Shh signaling center, the lateral floor plate, a crucial step to create the burst of Shh required for OPC specification. At the same time, FGFs prevent down-regulation of Olig2 in pMN progenitor cells as these cells receive higher threshold of the Shh signal. Finally, we bring arguments favoring a key role of newly differentiated neurons acting as providers of the FGF signal required to trigger OPC generation in the ventral spinal cord.

Conclusion

Altogether our data reveal that the FGF signaling pathway is activated and required for OPC commitment in the ventral spinal cord. More generally, our data may prove important in defining strategies to produce large populations of determined oligodendrocyte precursor cells from undetermined neural progenitors, including stem cells. In the long run, these new data could be useful in attempts to stimulate the oligodendrocyte fate in residing neural stem cells.

Mechanisms of cell-cell interaction in oligodendrogenesis and remyelination after stroke

White matter damage is a clinically important aspect of several central nervous system diseases, including stroke. Cerebral white matter primarily consists of axonal bundles ensheathed with myelin secreted by mature oligodendrocytes, which play an important role in neurotransmission between different areas of gray matter. During the acute phase of stroke, damage to oligodendrocytes leads to white matter dysfunction through the loss of myelin. On the contrary, during the chronic phase, white matter components promote an environment, which is favorable for neural repair, vascular remodeling, and remyelination. For effective remyelination to take place, oligodendrocyte precursor cells (OPCs) play critical roles by proliferating and differentiating into mature oligodendrocytes, which help to decrease the burden of axonal injury. Notably, other types of cells contribute to these OPC responses under the ischemic conditions. This mini-review summarizes the non-cell autonomous mechanisms in oligodendrogenesis and remyelination after white matter damage, focusing on how OPCs receive support from their neighboring cells. This article is part of a Special Issue entitled SI: Cell Interactions In Stroke.

Expression profiles of inka2 in the murine nervous system

Dynamic rearrangement of the actin cytoskeleton impacts many cellular characteristics in both the developing and adult central nervous systems (CNS), including the migration and adhesion of highly motile neural progenitor cells, axon guidance of immature neurons, and reconstruction of synaptic structures in the adult brain. Inka1, a known regulator of actin cytoskeleton reconstruction, is predominantly expressed by the neural crest cell lineage and regulates the migration and differentiation of these cells. In the present study, we identified a novel gene, designated as inka2, which is related to inka1. Inka2/fam212b is an evolutionarily conserved gene found in different vertebrate species and constitutes a novel gene family together with inka1. Northern blot analysis showed that inka2 mRNA was highly enriched in the nervous system. The spatiotemporal propagation cell profiles of those cells that expressed inka2 transcripts were compatible with those of Olig2-positive oligodendrocyte progenitor cells, which originate in the ventral ventricular zone during embryogenesis. Intense expression of inka2 was also noted in the proliferative neuronal progenitors in the developing cerebellum. On the other hand, immature newborn neurons in the embryonic brain showed no expression of inka2, except for the cells residing in the marginal zone of the embryonic telencephalon, which is known to contain transient cells including the non-subplate pioneer neurons and Cajal-Retzius cells. As brain development proceeds during the postnatal stage, inka2 expression emerged in some populations of immature neurons, including the neocortical pyramidal neurons, hippocampal pyramidal neurons, and granule cells migrating in the cerebellar cortex. In the adult brain, the expression of inka2 was interestingly confined in terminally differentiated neurons in the restricted forebrain regions. Taken together, as a novel regulator of actin cytoskeletons in the CNS, inka2 may be involved in multiple actin-driven processes, including cell migration and establishment of neuronal polarity.

Oligodendrocyte generation during mouse development

Oligodendrocytes (OLs) are glial cells, which generate myelin in the central nervous system. Their interesting developmental features attract many neurobiologists eager to study cell differentiation, gene expression regulation, or dynamic morphogenesis. Their primary role in protecting the axons has major impacts in the medical research field: in multiple sclerosis, a demyelinating disease in which remyelination is blocked. Oligodendrogenesis is involved in higher brain function including motor skill learning and cognitive function. Here, we review advances in the research on OL development and highlight areas where questions remain to be answered in both developmental biology and neurobiology related aspects.

An enhanced role and expanded developmental origins for gamma-aminobutyric acidergic interneurons in the human cerebral cortex

Human beings have considerably expanded cognitive abilities compared with all other species and they also have a relatively larger cerebral cortex compared with their body size. But is a bigger brain the only reason for higher cognition or have other features evolved in parallel? Humans have more and different types of GABAergic interneurons, found in different places, than our model species. Studies are beginning to show differences in function. Is this expanded repertoire of functional types matched by an evolution of their developmental origins? Recent studies support the idea that generation of interneurons in the ventral telencephalon may be more complicated in primates, which have evolved a large and complex outer subventricular zone in the ganglionic eminences. In addition, proportionally more interneurons appear to be produced in the caudal ganglionic eminence, the majority of which populate the superficial layers of the cortex. Whether or not the cortical proliferative zones are a source of interneurogenesis, and to what extent and of what significance, is a contentious issue. As there is growing evidence that conditions such as autism, schizophrenia and congenital epilepsy may have developmental origins in the failure of interneuron production and migration, it is important we understand fully the similarities and differences between human development and our animal models.

RAS/ERK signaling controls proneural genetic programs in cortical development and gliomagenesis

Neural cell fate specification is well understood in the embryonic cerebral cortex, where the proneural genes Neurog2 and Ascl1 are key cell fate determinants. What is less well understood is how cellular diversity is generated in brain tumors. Gliomas and glioneuronal tumors, which are often localized in the cerebrum, are both characterized by a neoplastic glial component, but glioneuronal tumors also have an intermixed neuronal component. A core abnormality in both tumor groups is overactive RAS/ERK signaling, a pro-proliferative signal whose contributions to cell differentiation in oncogenesis are largely unexplored. We found that RAS/ERK activation levels differ in two distinct human tumors associated with constitutively active BRAF. Pilocytic astrocytomas, which contain abnormal glial cells, have higher ERK activation levels than gangliogliomas, which contain abnormal neuronal and glial cells. Using in vivo gain of function and loss of function in the mouse embryonic neocortex, we found that RAS/ERK signals control a proneural genetic switch, inhibiting Neurog2 expression while inducing Ascl1, a competing lineage determinant. Furthermore, we found that RAS/ERK levels control Ascl1's fate specification properties in murine cortical progenitors--at higher RAS/ERK levels, Ascl1(+) progenitors are biased toward proliferative glial programs, initiating astrocytomas, while at moderate RAS/ERK levels, Ascl1 promotes GABAergic neuronal and less glial differentiation, generating glioneuronal tumors. Mechanistically, Ascl1 is phosphorylated by ERK, and ERK phosphoacceptor sites are necessary for Ascl1's GABAergic neuronal and gliogenic potential. RAS/ERK signaling thus acts as a rheostat to influence neural cell fate selection in both normal cortical development and gliomagenesis, controlling Neurog2-Ascl1 expression and Ascl1 function.

Proneural bHLH genes in development and disease

Proneural genes encode evolutionarily conserved basic-helix-loop-helix transcription factors. In Drosophila, proneural genes are required and sufficient to confer a neural identity onto naïve ectodermal cells, inducing delamination and subsequent neuronal differentiation. In vertebrates, proneural genes are expressed in cells that already have a neural identity, but they are still required and sufficient to initiate neurogenesis. In all organisms, proneural genes control neurogenesis by regulating Notch-mediated lateral inhibition and initiating the expression of downstream differentiation genes. The general mode of proneural gene function has thus been elucidated. However, the regulatory mechanisms that spatially and temporally control proneural gene function are only beginning to be deciphered. Understanding how proneural gene function is regulated is essential, as aberrant proneural gene expression has recently been linked to a variety of human diseases-ranging from cancer to neuropsychiatric illnesses and diabetes. Recent insights into proneural gene function in development and disease are highlighted herein.

Proneural genes in neocortical development

Neurons, astrocytes and oligodendrocytes arise from CNS progenitor cells at defined times and locations during development, with transcription factors serving as key determinants of these different neural cell fates. An emerging theme is that the transcription factors that specify CNS cell fates function in a context-dependent manner, regulated by post-translational modifications and epigenetic alterations that partition the genome (and hence target genes) into active or silent domains. Here we profile the critical roles of the proneural genes, which encode basic-helix-loop-helix (bHLH) transcription factors, in specifying neural cell identities in the developing neocortex. In particular, we focus on the proneural genes Neurogenin 1 (Neurog1), Neurog2 and Achaete scute-like 1 (Ascl1), which are each expressed in a distinct fashion in the progenitor cell pools that give rise to all of the neuronal and glial cell types of the mature neocortex. Notably, while the basic functions of these proneural genes have been elucidated, it is becoming increasingly evident that tight regulatory controls dictate when, where and how they function. Current efforts to better understand how proneural gene function is regulated will not only improve our understanding of neocortical development, but are also critical to the future development of regenerative therapies for the treatment of neuronal degeneration or disease.

Depletion of molecular chaperones from the endoplasmic reticulum and fragmentation of the Golgi apparatus associated with pathogenesis in Pelizaeus-Merzbacher disease

Missense mutations in the proteolipid protein 1 (PLP1) gene cause a wide spectrum of hypomyelinating disorders, from mild spastic paraplegia type 2 to severe Pelizaeus-Merzbacher disease (PMD). Mutant PLP1 accumulates in the endoplasmic reticulum (ER) and induces ER stress. However, the link between the clinical severity of PMD and the cellular response induced by mutant PLP1 remains largely unknown. Accumulation of misfolded proteins in the ER generally leads to up-regulation of ER chaperones to alleviate ER stress. Here, we found that expression of the PLP1-A243V mutant, which causes severe disease, depletes some ER chaperones with a KDEL (Lys-Asp-Glu-Leu) motif, in HeLa cells, MO3.13 oligodendrocytic cells, and primary oligodendrocytes. The same PLP1 mutant also induces fragmentation of the Golgi apparatus (GA). These organelle changes are less prominent in cells with milder disease-associated PLP1 mutants. Similar changes are also observed in cells expressing another disease-causing gene that triggers ER stress, as well as in cells treated with brefeldin A, which induces ER stress and GA fragmentation by inhibiting GA to ER trafficking. We also found that mutant PLP1 disturbs localization of the KDEL receptor, which transports the chaperones with the KDEL motif from the GA to the ER. These data show that PLP1 mutants inhibit GA to ER trafficking, which reduces the supply of ER chaperones and induces GA fragmentation. We propose that depletion of ER chaperones and GA fragmentation induced by mutant misfolded proteins contribute to the pathogenesis of inherited ER stress-related diseases and affect the disease severity.

In vitro expanded stem cells from the developing retina fail to generate photoreceptors but differentiate into myelinating oligodendrocytes

Cell transplantation to treat retinal degenerative diseases represents an option for the replacement of lost photoreceptor cells. In vitro expandable cells isolated from the developing mammalian retina have been suggested as a potential source for the generation of high numbers of donor photoreceptors. In this study we used standardized culture conditions based on the presence of the mitogens FGF-2 and EGF to generate high numbers of cells in vitro from the developing mouse retina. These presumptive ‘retinal stem cells’ (‘RSCs’) can be propagated as monolayer cultures over multiple passages, express markers of undifferentiated neural cells, and generate neuronal and glial cell types upon withdrawal of mitogens in vitro or following transplantation into the adult mouse retina. The proportion of neuronal differentiation can be significantly increased by stepwise removal of mitogens and inhibition of the notch signaling pathway. However, ‘RSCs’, by contrast to their primary counterparts in vivo, i.e. retinal progenitor cells, loose the expression of retina-specific progenitor markers like Rax and Chx10 after passaging and fail to differentiate into photoreceptors both in vitro or after intraretinal transplantation. Notably, ‘RSCs’ can be induced to differentiate into myelinating oligodendrocytes, a cell type not generated by primary retinal progenitor cells. Based on these findings we conclude that ‘RSCs’ expanded in high concentrations of FGF-2 and EGF loose their retinal identity and acquire features of in vitro expandable neural stem-like cells making them an inappropriate cell source for strategies aimed at replacing photoreceptor cells in the degenerated retina.

PDK1 regulates the generation of oligodendrocyte precursor cells at an early stage of mouse telencephalic development

During the development of the mouse telencephalon, multipotent neural precursor cells (NPCs) generate oligodendrocyte precursor cells (OPCs), progenitors restricted to the oligodendrocyte lineage, at various sites in a developmental stage-dependent manner. Although substantial progress has been made in identifying the transcription factors that control the production of OPCs, the signaling pathways that regulate these transcription factors and the spatiotemporal pattern of OPC production have been only partially clarified. Here, we show that the serine-threonine kinase 3-phosphoinositide-dependent kinase 1 (PDK1) contributes to an early wave of OPC production in the developing mouse telencephalon. Ablation of PDK1 in NPCs resulted in a reduction in the number of OPCs positive for Sox10 and platelet-derived growth factor receptor α (PDGFRα) within the neocortex and striatum at embryonic day (E) 15.5, but not at E18.5. Furthermore, pharmacological inhibition of phosphoinositide 3-kinase (PI3K) or deletion of the PDK1 gene suppressed the generation of OPCs from NPCs induced by fibroblast growth factor (FGF) 2 in culture. These results implicate the PI3K-PDK1 pathway in the physiological regulation of OPC production in a developmental context-dependent manner.

Deriving excitatory neurons of the neocortex from pluripotent stem cells

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

Fibroblast growth factor signaling is required for the generation of oligodendrocyte progenitors from the embryonic forebrain

Fibroblast growth factors (FGFs) comprise a family of developmental regulators implicated in a wide variety of neurological functions. FGF receptors 1, 2, and 3 (Fgfrs) are expressed in the embryonic forebrain, including regions overlapping with ventral sites of oligodendrocyte progenitor (OLP) generation. Although FGF signaling is known to influence the proliferation of OLPs in vitro, functions of different Fgfrs in vivo are lacking. Here, we examined single and double mutants with conditional disruption of Fgfrs, specifically in the embryonic forebrain, to investigate the effect of FGFs on the generation and proliferation of OLPs in vivo. FGF signaling, through cooperation between Fgfr1 and Fgfr2 but not Fgfr3, is required for the initial generation of OLPs in the mouse ventral forebrain, with Fgfr1 being a stronger inducer than Fgfr2. In cultures derived from embryonic mutant forebrains or from normal forebrains grown in the presence of Fgfr inhibitor, a strong attenuation of OLP generation was observed, supporting the role of FGF signaling in vivo. Contrary to in vitro findings, Fgfr1 and Fgfr2 signaling is not required for the proliferation of OLPs in vivo. Finally, failure of OLP generation in the Fgfr mutants occurred without loss of sonic hedgehog (Shh) signaling; and pharmacological inhibition of either Fgfr or hedgehog signaling in parallel cultures strongly inhibited OLP generation, suggesting that Fgfrs cooperate with Shh to generate OLPs. Overall, our results reveal for the first time an essential role of FGF signaling in vivo, where the three Fgfrs differentially control the normal generation of OLPs from the embryonic ventral forebrain.

SOX2 expression levels distinguish between neural progenitor populations of the developing dorsal telencephalon

The HMG-Box transcription factor SOX2 is expressed in neural progenitor populations throughout the developing and adult central nervous system and is necessary to maintain their progenitor identity. However, it is unclear whether SOX2 levels are uniformly expressed across all neural progenitor populations. In the developing dorsal telencephalon, two distinct populations of neural progenitors, radial glia and intermediate progenitor cells, are responsible for generating a majority of excitatory neurons found in the adult neocortex. Here we demonstrate, using both cellular and molecular analyses, that SOX2 is differentially expressed between radial glial and intermediate progenitor populations. Moreover, utilizing a SOX2(EGFP) mouse line, we show that this differential expression can be used to prospectively isolate distinct, viable populations of radial glia and intermediate cells for in vitro analysis. Given the limited repertoire of cell-surface markers currently available for neural progenitor cells, this provides an invaluable tool for prospectively identifying and isolating distinct classes of neural progenitor cells from the central nervous system.

Transcription factors and neural stem cell self-renewal, growth and differentiation

The central nervous system (CNS) is a large network of interconnecting and intercommunicating cells that form functional circuits. Disease and injury of the CNS are prominent features of the healthcare landscape. There is an urgent unmet need to generate therapeutic solutions for CNS disease/injury. To increase our understanding of the CNS we need to generate cellular models that are experimentally tractable. Neural stem cells (NSCs), cells that generate the CNS during embryonic development, have been identified and propagated in vitro. To develop NSCs as a cellular model for the CNS we need to understand more about their genetics and cell biology. In particular, we need to define the mechanisms of self-renewal, proliferation and differentiation--i.e. NSC behavior. The analysis of pluripotency of embryonic stem cells through mapping regulatory networks of transcription factors has proven to be a powerful approach to understanding embryonic development. Here, we discuss the role of transcription factors in NSC behavior.

Opposing effects of retinoid signaling on astrogliogenesis in embryonic day 13 and 17 cortical progenitor cells

All-trans retinoic acid (RA) is a differentiation factor in many tissues. However, its role in astrogliogenesis has not been extensively studied. Here, we investigated the effect of RA on the regulation of astrogliogenesis at different cortical developmental stages. We prepared rat cortical progenitor cells from embryonic day (E) 13 and E17, which correspond to the beginning of neurogenic and astrogliogenic periods, respectively. Surprisingly, RA promoted astrogliogenesis at E17 but inhibited astrogliogenesis induced by ciliary neurotrophic factor (CNTF) at E13. The inhibitory effect of RA on astrogliogenesis at E13 was not due to premature commitment of progenitors to a neuronal or oligodendroglial lineage. Rather, RA retained more progenitors in a proliferative state. Furthermore, RA inhibition of astrogliogenesis at E13 was independent of STAT3 signaling and required the function of the alpha and beta isoforms of the RA receptors (RAR). Moreover, the differential response of E13 and E17 progenitors to RA was due to differences in the intrinsic properties of these cells that are preserved in vitro. The inhibitory effect of RA on cytokine-induced astrogliogenesis at E13 may contribute to silencing of any potential precocious astrogliogenesis during the neurogenic period.

Fibroblast growth factor 2 maintains the neurogenic capacity of embryonic neural progenitor cells in vitro but changes their neuronal subtype specification

Many in vitro systems used to examine multipotential neural progenitor cells (NPCs) rely on mitogens including fibroblast growth factor 2 (FGF2) for their continued expansion. However, FGF2 has also been shown to alter the expression of transcription factors (TFs) that determine cell fate. Here, we report that NPCs from the embryonic telencephalon grown without FGF2 retain many of their in vivo characteristics, making them a good model for investigating molecular mechanisms involved in cell fate specification and differentiation. However, exposure of cortical NPCs to FGF2 results in a profound change in the types of neurons generated, switching them from a glutamatergic to a GABAergic phenotype. This change closely correlates with the dramatic upregulation of TFs more characteristic of ventral telencephalic NPCs. In addition, exposure of cortical NPCs to FGF2 maintains their neurogenic potential in vitro, and NPCs spontaneously undergo differentiation following FGF2 withdrawal. These results highlight the importance of TFs in determining the types of neurons generated by NPCs in vitro. In addition, they show that FGF2, as well as acting as a mitogen, changes the developmental capabilities of NPCs. These findings have implications for the cell fate specification of in vitro-expanded NPCs and their ability to generate specific cell types for therapeutic applications. Disclosure of potential conflicts of interest is found at the end of this article.

The effects of soluble growth factors on embryonic stem cell differentiation inside of fibrin scaffolds

The goal of this research was to determine the effects of different growth factors on the survival and differentiation of murine embryonic stem cell-derived neural progenitor cells (ESNPCs) seeded inside of fibrin scaffolds. Embryoid bodies were cultured for 8 days in suspension, retinoic acid was applied for the final 4 days to induce ESNPC formation, and then the EBs were seeded inside of three-dimensional fibrin scaffolds. Scaffolds were cultured in the presence of media containing different doses of the following growth factors: neurotrophin-3 (NT-3), basic fibroblast growth factor (bFGF), platelet-derived growth factor (PDGF)-AA, ciliary neurotrophic factor, and sonic hedgehog (Shh). The cell phenotypes were characterized using fluorescence-activated cell sorting and immunohistochemistry after 14 days of culture. Cell viability was also assessed at this time point. Shh (10 ng/ml) and NT-3 (25 ng/ml) produced the largest fractions of neurons and oligodendrocytes, whereas PDGF (2 and 10 ng/ml) and bFGF (10 ng/ml) produced an increase in cell viability after 14 days of culture. Combinations of growth factors were tested based on the results of the individual growth factor studies to determine their effect on cell differentiation. The incorporation of ESNPCs and growth factors into fibrin scaffolds may serve as potential treatment for spinal cord injury.

The expression and functions of glycoconjugates in neural stem cells

The mammalian central nervous system is organized by a variety of cells such as neurons and glial cells. These cells are generated from a common progenitor, the neural stem cell (NSC). NSCs are defined as undifferentiated neural cells that are characterized by their high proliferative potential while retaining the capacity for self-renewal and multipotency. Glycoconjugates carrying carbohydrate antigens, including glycoproteins, glycolipids, and proteoglycans, are primarily localized on the plasma-membrane surface of cells and serve as excellent biomarkers at various stages of cellular differentiation. Moreover, they also play important functional roles in determining cell fate such as self-renewal, proliferation, and differentiation. In the present review, we discuss the expression pattern and possible functions of glycoconjugates and carbohydrate antigens in NSCs, with an emphasis on stage-specific embryonic antigen-1, human natural killer antigen-1, polysialic acid-neural cell-adhesion molecule, prominin-1, gp130, chondroitin sulfate proteoglycans, heparan sulfate proteoglycans, cystatin C, galectin-1, glycolipids, and Notch.

Induction of oligodendrocyte progenitors in dorsal forebrain by intraventricular microinjection of FGF-2

During embryonic development, oligodendrocyte progenitors (OLPs) originate from the ventral forebrain under the regulation of Sonic hedgehog (Shh). Shh controls the expression of transcription factor Olig2, which is strongly implicated in OLP generation. Studies of mice deficient in Shh expression suggest, however, that an alternative pathway for OLP generation may exist. The generation of OLPs in dorsal forebrain has been suggested since treatment of dorsal-neural progenitor cells in culture with fibroblast growth factor (FGF-2) results in OLP induction. To ask if dorsal induction of OLPs in embryonic forebrain can occur in vivo and if FGF-2 could initiate an alternative pathway of regulation, we used in utero microinjection of FGF-2 into the lateral ventricles of mouse fetal forebrain. A single injection of FGF-2 at E13.5 resulted in the expression of the OLP markers Olig2 and PDGFRalpha mRNA in dorsal forebrain ventricular and intermediate zones. However, FGF-2 did not induce dorsal expression of Shh, Patched1 or Nkx2.1, and co-injection of FGF-2 and a Shh inhibitor did not attenuate the induction of Olig2 and PDGFRalpha, suggesting that Shh signaling was not involved in this FGF-2-mediated dorsal induction. These results demonstrate that the dorsal embryonic forebrain in vivo has the potential to generate OLPs in the presence of normal positional cues and that this can be driven by FGF-2 independent of Shh signaling.