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

Immediate protein expression from exogenous mRNAs in embryonic brain

mRNA vaccines for SARS-CoV-2 have been widely used and saving millions of people in the world. How efficiently proteins are produced from exogenous mRNAs in the embryonic brain, however, is less known. Here we show that protein expression occurs highly efficiently in neural stem cells, in a very narrow time window after mRNA electroporation in the embryonic mouse brain, where plasmids have been successfully transfected. Protein expression is detected 1 h and 12 h after the electroporation of mRNAs and plasmids, respectively. The delivery of exogenous mRNAs may be useful for not only vaccines but also functional analysis in the brain.

White matter disturbances in phenylketonuria: Possible underlying mechanisms

White matter pathologies, as well as intellectual disability, microcephaly, and other central nervous system injuries, are clinical traits commonly ascribed to classic phenylketonuria (PKU). PKU is an inherited metabolic disease elicited by the deficiency of phenylalanine hydroxylase. Accumulation of l-phenylalanine (Phe) and its metabolites is found in tissues and body fluids in phenylketonuric patients. In order to mitigate the clinical findings, rigorous dietary Phe restriction constitutes the core of therapeutic management in PKU. Myelination is the process whereby the oligodendrocytes wrap myelin sheaths around the axons, supporting the conduction of action potentials. White matter injuries are implicated in the brain damage related to PKU, especially in untreated or poorly treated patients. The present review summarizes evidence toward putative mechanisms driving the white matter pathology in PKU patients.

Rapid and Efficient Differentiation of Rodent Neural Stem Cells into Oligodendrocyte Progenitor Cells

Oligodendrocyte progenitor cells (OPCs) may have beneficial effects in cell replacement therapy of neurodegenerative disease owing to their unique capability to differentiate into myelinogenic oligodendrocytes (OLs) in response to extrinsic signals. Therefore, it is of significance to establish an effective differentiation methodology to generate highly pure OPCs and OLs from some easily accessible stem cell sources. To achieve this goal, in this study, we present a rapid and efficient protocol for oligodendroglial lineage differentiation from mouse neural stem cells (NSCs), rat NSCs, or mouse embryonic stem cell-derived neuroepithelial stem cells. In a defined culture medium containing Smoothened Agonist, basic fibroblast growth factor, and platelet-derived growth factor-AA, OPCs could be generated from the above stem cells over a time course of 4–6 days, achieving a cell purity as high as ∼90%. In particular, these derived OPCs showed high expandability and could further differentiate into myelin basic protein-positive OLs within 3 days or alternatively into glial fibrillary acidic protein-positive astrocytes within 7 days. Furthermore, transplantation of rodent NSC-derived OPCs into injured spinal cord indicated that it is a feasible strategy to treat spinal cord injury. Our results suggest a differentiation strategy for robust production of OPCs and OLs from rodent stem cells, which could provide an abundant OPC source for spinal cord injury.

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.

Temporal Changes in Transcription Factor Expression Associated with the Differentiation State of Cerebellar Neural Stem/Progenitor Cells During Development

During central nervous development, multi-potent neural stem/progenitor cells located in the ventricular/subventricular zones are temporally regulated to mostly produce neurons during early developmental stages and to produce glia during later developmental stages. After birth, the rodent cerebellum undergoes further dramatic development. It is also known that neural stem/progenitor cells are present in the white matter (WM) of the postnatal cerebellum until around P10, although the fate of these cells has yet to be determined. In the present study, it was revealed that primary neurospheres generated from cerebellar neural stem/progenitor cells at postnatal day 3 (P3) mainly differentiated into astrocytes and oligodendrocytes. In contrast, primary neurospheres generated from cerebellar neural stem/progenitor cells at P8 almost exclusively differentiated into astrocytes, but not oligodendrocytes. These results suggest that the differentiation potential of primary neurospheres changes depending on the timing of neural stem/progenitor cell isolation from the cerebellum. To identify the candidate transcription factors involved in regulating this temporal change, we utilized DNA microarray analysis to compare global gene-expression profiles of primary neurospheres generated from neural stem/progenitor cells isolated from either P3 or P8 cerebellum. The expression of zfp711, zfp618, barx1 and hoxb3 was higher in neurospheres generated from P3 cerebellum than from P8 by real-time quantitative PCR. Several precursor cells were found to express zfp618, barx1 or hoxb3 in the WM of the cerebellum at P3, but these transcription factors were absent from the WM of the P8 cerebellum.

Origin of oligodendrocytes in mammalian forebrains: a revised perspective

Oligodendrocyte precursor cells (OPCs) appear in the late embryonic brain, mature into oligodendrocytes (OLs), and form myelin in the postnatal brain. It has been proposed that early born OPCs derived from the ventral forebrain are eliminated postnatally and late-born OLs predominate in the adult mouse cortex. However, the temporal and regional niche for cortical OL generation, which persists throughout life in adult mammals, remains to be determined. Our recent study provides new insight into self-renewing and multipotent neural stem cells (NSCs). Our results, together with previous studies, suggest that NSCs at the dorsoventral boundary are uniquely specialized to produce myelin-forming OLs in the cortex during a restricted temporal window. These findings may help identify transcription factors or gene expression patterns which confer neural precursors with the characteristic ability of dorsoventral boundary NSCs to differentiate into OLs, and facilitate the development of new strategies for regenerative medicine of the damaged brain.

Mosaic Subventricular Origins of Forebrain Oligodendrogenesis

In the perinatal as well as the adult CNS, the subventricular zone (SVZ) of the forebrain is the largest and most active source of neural stem cells (NSCs) that generates neurons and oligodendrocytes (OLs), the myelin forming cells of the CNS. Recent advances in the field are beginning to shed light regarding SVZ heterogeneity, with the existence of spatially segregated microdomains that are intrinsically biased to generate phenotypically distinct neuronal populations. Although most research has focused on this regionalization in the context of neurogenesis, newer findings underline that this also applies for the genesis of OLs under the control of specific patterning molecules. In this mini review, we discuss the origins as well as the mechanisms that induce and maintain SVZ regionalization. These come in the flavor of specific signaling ligands and subsequent initiation of transcriptional networks that provide a basis for subdividing the SVZ into distinct lineage-specific microdomains. We further emphasize canonical Wnts and FGF2 as essential signaling pathways for the regional genesis of OL progenitors from NSCs of the dorsal SVZ. This aspect of NSC biology, which has so far received little attention, may unveil new avenues for appropriately recruiting NSCs in demyelinating diseases.

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.

FGF-2 signal promotes proliferation of cerebellar progenitor cells and their oligodendrocytic differentiation at early postnatal stage

The origins and developmental regulation of cerebellar oligodendrocytes are largely unknown, although some hypotheses of embryonic origins have been suggested. Neural stem cells exist in the white matter of postnatal cerebellum, but it is unclear whether these neural stem cells generate oligodendrocytes at postnatal stages. We previously showed that cerebellar progenitor cells, including neural stem cells, widely express CD44 at around postnatal day 3. In the present study, we showed that CD44-positive cells prepared from the postnatal day 3 cerebellum gave rise to neurospheres, while CD44-negative cells prepared from the same cerebellum did not. These neurospheres differentiated mainly into oligodendrocytes and astrocytes, suggesting that CD44-positive neural stem/progenitor cells might generate oligodendrocytes in postnatal cerebellum. We cultured CD44-positive cells from the postnatal day 3 cerebellum in the presence of signaling molecules known as mitogens or inductive differentiation factors for oligodendrocyte progenitor cells. Of these, only FGF-2 promoted survival and proliferation of CD44-positive cells, and these cells differentiated into O4+ oligodendrocytes. Furthermore, we examined the effect of FGF-2 on cerebellar oligodendrocyte development ex vivo. FGF-2 enhanced proliferation of oligodendrocyte progenitor cells and increased the number of O4+ and CC1+ oligodendrocytes in slice cultures. These results suggest that CD44-positive cells might be a source of cerebellar oligodendrocytes and that FGF-2 plays important roles in their development at an early postnatal stage.

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.

Optimizing culture medium composition to improve oligodendrocyte progenitor cell yields in vitro from subventricular zone-derived neural progenitor cell neurospheres

Neural Stem and Progenitor Cells (NSC/NPC) are gathering tangible recognition for their uses in cell therapy and cell replacement therapies for human disease, as well as a model system to continue research on overall neural developmental processes in vitro. The Subventricular Zone is one of the largest NSC/NPC niches in the developing mammalian Central Nervous System, and persists through to adulthood. Oligodendrocyte progenitor cell (OPC) enriched cultures are usefull tools for in vitro studies as well as for cell replacement therapies for treating demyelination diseases. We used Subventricular Zone-derived NSC/NPC primary cultures from newborn mice and compared the effects of different growth factor combinations on cell proliferation and OPC yield. The Platelet Derived Growth Factor-AA and BB homodimers had a positive and significant impact on OPC generation. Furthermore, heparin addition to the culture media contributed to further increase overall culture yields. The OPC generated by this protocol were able to mature into Myelin Basic Protein-expressing cells and to interact with neurons in an in vitro co-culture system. As a whole, we describe an optimized in vitro method for increasing OPC.

Bre1a, a histone H2B ubiquitin ligase, regulates the cell cycle and differentiation of neural precursor cells

Cell cycle regulation is crucial for the maintenance of stem cell populations in adult mammalian tissues. During development, the cell cycle length in neural stem cells increases, which could be associated with their capabilities for self-renewal. However, the molecular mechanisms that regulate differentiation and cell cycle progression in embryonic neural stem cells remain largely unknown. Here, we investigated the function of Bre1a, a histone H2B ubiquitylation factor, which is expressed in most but not all of neural precursor cells (NPCs) in the developing mouse brain. We found that the knockdown of Bre1a in NPCs lengthened their cell cycle through the upregulation of p57(kip2) and the downregulation of Cdk2. In addition, the knockdown of Bre1a increased the expression of Hes5, an effector gene of Notch signaling, through the action of Fezf1 and Fezf2 genes and suppressed the differentiation of NPCs. Our data suggest that Bre1a could be a bifunctional gene that regulates both the differentiation status and cell cycle length of NPCs. We propose a novel model that the Bre1a-negative cells in the ventricular zone of early embryonic brains remain undifferentiated and are selected as self-renewing neural stem cells, which increase their cell cycle time during development.

NG2 cells in white matter but not gray matter proliferate in response to PDGF

Glial cells that express the NG2 proteoglycan and the α receptor for PDGF (NG2 cells, polydendrocytes) make up the fifth major cell population that serves as oligodendrocyte progenitor cells in the postnatal CNS. Although recent studies have suggested differences in their proliferation and oligodendrocyte differentiation in gray and white matter, the mechanism underlying the observed differences has been unclear. Using organotypic slice cultures from the forebrain and cerebellum of early postnatal NG2creBAC:ZEG mice, we have compared basal and growth factor-induced proliferation of NG2 cells in gray and white matter. NG2 cells in white matter exhibited greater proliferative response to PDGF AA than those in gray matter. Heterotopic slice transplant and explant cultures suggested intrinsic mechanisms for the differential proliferative response of gray and white matter cells. Additionally, younger white matter NG2 cells showed a more robust proliferative response to PDGF. Basal and PDGF-induced proliferation of gray and white matter NG2 cells was largely dependent on Wnt/β-catenin and phosphatidylinositol 3-kinase acting through the mammalian target of rapamycin pathway and not through ERK. These data uncover a previously unrecognized divergence between gray and white matter NG2 cells in the developing brain in their proliferative response to PDGF.

The Lewis X-related α1,3-fucosyltransferase, Fut10, is required for the maintenance of stem cell populations

Lewis X (Le(X), Galβ1-4(Fucα1-3)GlcNAc) is a carbohydrate epitope that is present at the nonreducing terminus of sugar chains of glycoproteins and glycolipids, and is abundantly expressed in several stem cell populations. Le(X) antigen can be used in conjunction with fluorescence-activated cell sorting to isolate neurosphere-forming neural stem cells (NSCs) from embryonic mouse brains. However, its function in the maintenance and differentiation of stem cells remains largely unknown. In this study, we examined mice deficient for fucosyltransferase 9 (Fut9), which is thought to synthesize most, if not all, of the Le(X) moieties in the brain. We found that the number of NSCs was increased in the brain of Fut9(-/-) embryos, suggesting that Fut9-synthesized Le(X) is dispensable for the maintenance of NSCs. Another α1,3-fucosyltransferase gene, fucosyltransferase 10 (Fut10), is expressed in the ventricular zone of the embryonic brain. Overexpression of Fut10 enhanced the self-renewal of NSCs. Conversely, suppression of Fut10 expression induced the differentiation of NSCs and embryonic stem cells. In addition, knockdown of Fut10 expression in the cortical ventricular zone of the embryonic brain by in utero electroporation of Fut10-miRNAs impaired the radial migration of neural precursor cells. Our data suggest that Fut10 is involved in a unique α1,3-fucosyltransferase activity with stringent substrate specificity, and that this activity is required to maintain stem cells in an undifferentiated state.

Receptor tyrosine kinase (RTK) signalling in the control of neural stem and progenitor cell (NSPC) development

Important developmental responses are elicited in neural stem and progenitor cells (NSPC) by activation of the receptor tyrosine kinases (RTK), including the fibroblast growth factor receptors, epidermal growth factor receptor, platelet-derived growth factor receptors and insulin-like growth factor receptor (IGF1R). Signalling through these RTK is necessary and sufficient for driving a number of developmental processes in the central nervous system. Within each of the four RTK families discussed here, receptors are activated by sets of ligands that do not cross-activate receptors of the other three families, and therefore, their activation can be independently regulated by ligand availability. These RTK pathways converge on a conserved core of signalling molecules, but differences between the receptors in utilisation of signalling molecules and molecular adaptors for intracellular signal propagation become increasingly apparent. Intracellular inhibitors of RTK signalling are widely involved in the regulation of developmental signalling in NSPC and often determine developmental outcomes of RTK activation. In addition, cellular responses of NSPC to the activation of a given RTK may be significantly modulated by signal strength. Cellular propensity to respond also plays a role in developmental outcomes of RTK signalling. In combination, these mechanisms regulate the balance between NSPC maintenance and differentiation during development and in adulthood. Attribution of particular developmental responses of NSPC to specific pathways of RTK signalling becomes increasingly elucidated. Co-activation of several RTK in developing NSPC is common, and analysis of co-operation between their signalling pathways may advance knowledge of RTK role in NSPC development.

Coordinated control of oligodendrocyte development by extrinsic and intrinsic signaling cues

Oligodendrocytes, the myelin-forming cells for axon ensheathment in the central nervous system, are critical for maximizing and maintaining the conduction velocity of nerve impulses and proper brain function. Demyelination caused by injury or disease together with failure of myelin regeneration disrupts the rapid propagation of action potentials along nerve fibers, and is associated with acquired and inherited disorders, including devastating multiple sclerosis and leukodystrophies. The molecular mechanisms of oligodendrocyte myelination and remyelination remain poorly understood. Recently, a series of signaling pathways including Shh, Notch, BMP and Wnt signaling and their intracellular effectors such as Olig1/2, Hes1/5, Smads and TCFs, have been shown to play important roles in regulating oligodendrocyte development and myelination. In this review, we summarize our recent understanding of how these signaling pathways modulate the progression of oligodendrocyte specification and differentiation in a spatiotemporally-specific manner. A better understanding of the complex but coordinated function of extracellular signals and intracellular determinants during oligodendrocyte development will help to devise effective strategies to promote myelin repair for patients with demyelinating diseases.

MEK Is a Key Regulator of Gliogenesis in the Developing Brain

We have defined functions of MEK in regulating gliogenesis in developing cerebral cortex using loss- and gain-of-function mouse genetics. Radial progenitors deficient in both Mek1 and Mek2 fail to transition to the gliogenic mode in late embryogenesis, and astrocyte and oligodendroglial precursors fail to appear. In exploring mechanisms, we found that the key cytokine-regulated gliogenic pathway is attenuated. Further, the Ets transcription family member Etv5/Erm is strongly regulated by MEK and Erm overexpression can rescue the gliogenic potential of Mek-deleted progenitors. Remarkably, Mek1/2-deleted mice surviving postnatally exhibit cortices almost devoid of astrocytes and oligodendroglia and exhibit neurodegeneration. Conversely, expression of constitutively active MEK1 leads to a major increase in numbers of astrocytes in the adult brain. We conclude that MEK is essential for acquisition of gliogenic competence by radial progenitors and that levels of MEK activity regulate gliogenesis in the developing cortex.

Intraventricular injection of FGF-2 promotes generation of oligodendrocyte-lineage cells in the postnatal and adult forebrain

FGF2 is considered a key factor in the generation of oligodendrocytes (OLs) derived from neural stem cells (NSCs) located within the subventricular zone (SVZ). Here, we have examined FGF2 signaling in the forebrain of postnatal and adult mice. Using qPCR of microdissected microdomains of the dorsal SVZ (dSVZ) and lateral SVZ (lSVZ), and prominin1-sorted NSCs purified from these microdomains, we show that transcripts for FGF receptor 1 (FGFR1) and FGFR2 are enriched in the dSVZ, from which OLs are largely derived, whereas FGFR3 are significantly enriched within prominen1-sorted NSC of the lSVZ, which mainly generate olfactory interneurons. We show that direct administration of FGF2 into the lateral ventricle increased the generation of oligodendrocyte progenitors (OPCs) throughout the SVZ, both within the dSVZ and ectopically in the lSVZ and ependymal wall of the SVZ. Furthermore, FGF2 stimulated proliferation of neural progenitors (NPs) and their differentiation into OPCs. The results indicate that FGF2 increased specification of OPCs, inducing NPs to follow an oligodendrocyte developmental pathway. Notably, FGF2 did not block OPC differentiation and increased the number of oligodendrocytes in the periventricular white matter (PVWM) and cortex. However, FGF2 markedly disrupted myelination in the PVWM. A key finding was that FGF2 had equivalent actions on the generation of OPCs and myelin disruption in postnatal and adult mice. This study demonstrates a central role for FGF2 in promoting oligodendrocyte generation in the developing and adult brain.

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.

From cradle to grave: the multiple roles of fibroblast growth factors in neural development

The generation of a functional nervous system involves a multitude of steps that are controlled by just a few families of extracellular signaling molecules. Among these, the fibroblast growth factor (FGF) family is particularly prominent for the remarkable diversity of its functions. FGFs are best known for their roles in the early steps of patterning of the neural primordium and proliferation of neural progenitors. However, other equally important functions have emerged more recently, including in the later steps of neuronal migration, axon navigation, and synaptogenesis. We review here these diverse functions and discuss the mechanisms that account for this unusual range of activities. FGFs are essential components of most protocols devised to generate therapeutically important neuronal populations in vitro or to stimulate neuronal repair in vivo. How FGFs promote the development of the nervous system and maintain its integrity will thus remain an important focus of research in the future.

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.

Genetically modified human umbilical cord blood cells expressing vascular endothelial growth factor and fibroblast growth factor 2 differentiate into glial cells after transplantation into amyotrophic lateral sclerosis transgenic mice

Current therapy of a number of neuropsychiatric maladies has only symptomatic modality. Effective treatment of these neuro-degenerative diseases, including amyotrophic lateral sclerosis (ALS), may benefit from combined gene/stem-cell approaches. In this report, mononuclear fraction of human umbilical cord blood cells (hUCBCs) were transfected by electroporation with dual plasmid constructs, simultaneously expressing vascular endothelial growth factor 165 (VEGF(165)) and human fibroblast growth factor 2 (FGF(2)) (pBud-VEGF-FGF(2)). These genetically modified hUCBCs were injected retro-orbitally into presymptomatic ALS transgenic animal models ((G)93(A) mice). Lumbar spinal cords of rodents were processed for immunofluoresent staining with antibodies against human nuclear antigen (HNA), oligodendrocyte-specific protein, S100, iba1, neuronal β(3)-tubulin and CD34. Co-localization of HNA and S100 was found in the spinal cord of mice after transplantation of genetically modified hUCBCs over-expressing VEGF-FGF(2). Double staining in control animals treated with unmodified hUCBCs, however, revealed HNA+ cells expressing iba1 and CD34. Neuron-specific β(3)-tubulin or oligodendrocyte-specific protein were not expressed in hUCBCs in either control or experimental mice. These results demonstrate that genetically naïve hUCBCs may differentiate into endothelial (CD34+) and microglial (iba1+) cells; however when over-expressing VEGF-FGF(2), hUCBCs transform into astrocytes (S100+). Autocrine regulation of VEGF and FGF(2) on hUCBCs, signal molecules from dying motor neurons in spinal cord, as well as self-differentiating potential may provide a unique microenvironment for the transformation of hUCBCs into astrocytes that eventually serve as a source of growth factors to enhance the survive potential of surrounding cells in the diseased regions.

FGF-receptor signalling controls neural cell diversity in the zebrafish hindbrain by regulating olig2 and sox9

The mechanisms underlying the generation of neural cell diversity are the subject of intense investigation, which has highlighted the involvement of different signalling molecules including Shh, BMP and Wnt. By contrast, relatively little is known about FGF in this process. In this report we identify an FGF-receptor-dependent pathway in zebrafish hindbrain neural progenitors that give rise to somatic motoneurons, oligodendrocyte progenitors and differentiating astroglia. Using a combination of chemical and genetic approaches to conditionally inactivate FGF-receptor signalling, we investigate the role of this pathway. We show that FGF-receptor signalling is not essential for the survival or maintenance of hindbrain neural progenitors but controls their fate by coordinately regulating key transcription factors. First, by cooperating with Shh, FGF-receptor signalling controls the expression of olig2, a patterning gene essential for the specification of somatic motoneurons and oligodendrocytes. Second, FGF-receptor signalling controls the development of both oligodendrocyte progenitors and astroglia through the regulation of sox9, a gliogenic transcription factor the function of which we show to be conserved in the zebrafish hindbrain. Overall, for the first time in vivo, our results reveal a mechanism of FGF in the control of neural cell diversity.

Olig2 transcription factor in the developing and injured forebrain; cell lineage and glial development

Olig2 transcription factor is widely expressed throughout the central nervous system; therefore, it is considered to have multiple functions in the developing, mature and injured brain. In this mini-review, we focus on Olig2 in the forebrain (telencephalon and diencephalon) and discuss the functional significance of Olig2 and the differentiation properties of Olig2-expressing progenitors in the development and injured states. Short- and long-term lineage analysis in the developing forebrain elucidated that not all late Olig2+ cells are direct cohorts of early cells and that Olig2 lineage cells differentiate into neurons or glial cells in a region- and stage-dependent manner. Olig2-deficient mice revealed large elimination of oligodendrocyte precursor cells and a decreased number of astrocyte progenitors in the dorsal cortex, whereas no reduction in the number of GABAergic neurons. In addition to Olig2 function in the developing cortex, Olig2 is also reported to be important for glial scar formation after injury. Thus, Olig2 can be essential for glial differentiation during development and after injury.

Generation of spinal motor neurons from human fetal brain-derived neural stem cells: role of basic fibroblast growth factor

Neural stem cells (NSCs) have some specified properties but are generally uncommitted and so can change their fate after exposure to environmental cues. It is unclear to what extent this NSC plasticity can be modulated by extrinsic cues and what are the molecular mechanisms underlying neuronal fate determination. Basic fibroblast growth factor (bFGF) is a well-known mitogen for proliferating NSCs. However, its role in guiding stem cells for neuronal subtype specification is undefined. Here we report that in-vitro-expanded human fetal forebrain-derived NSCs can generate cholinergic neurons with spinal motor neuron properties when treated with bFGF within a specific time window. bFGF induces NSCs to express the motor neuron marker Hb9, which is blocked by specific FGF receptor inhibitors and bFGF neutralizing antibodies. This development of spinal motor neuron properties is independent of selective proliferation or survival and does not require high levels of MAPK activation. Thus our study indicates that bFGF can play an important role in modulating plasticity and neuronal fate of human NSCs and presumably has implications for exploring the full potential of brain NSCs for clinical applications, particularly in spinal motor neuron regeneration.