Cerebellum- and forebrain-derived stem cells possess intrinsic regional character

Low-Density Primary Cell Culture of Postnatal Murine Cerebellar Progenitors In Vitro

Cerebellum is the major player of motor functions of the body, as well as being involved in plenty of nonmotor behavior traits. There are numerous disorders related to cerebellum that have severe consequences for patients and the absence of an effective treatment, so it is crucial to emphasize conducting research directed to deeply understand the biology of this structure, giving special importance to stem cells that could have regenerative potential. Here, we describe a novel protocol for isolating neural stem cells from postnatal mouse cerebellum, allowing for the study of progenitor cells from three distinct proliferative niches. Cells are maintained in low-density cultures without external growth factors, facilitating the study of intrinsic programming. We also suggest numerous applications that could provide an insight into the identity, development, and behavior of progenitor cells, which may contribute to the development of treatments for cerebellar disorders.

Human olfactory neurosphere-derived cells: a unified tool for neurological disease modelling and neurotherapeutic applications

As one of the leading causes of global mortality and morbidity, various neurological diseases cause social and economic burdens. Despite significant advances in the treatment of neurological diseases, establishing a proper disease model, especially for degenerative and infectious diseases, remains a major challenging issue. For long, mice were the model of choice but suffered from serious drawbacks of differences in anatomical and functional aspects of the nervous system. Furthermore, the collection of postmortem brain tissues limits their usage in cultured cell lines. Overcoming such limitations has prompted the usage of stem cells derived from the peripheral nervous system, such as the cells of the olfactory mucosa as a preferred choice. These cells can be easily cultured in vitro and retain the receptors of neuronal cells life-long. Such cells have various advantages over embryonic or induced stem cells, including homology, and ease of culture and can be conveniently obtained from diseased individuals through either biopsies or exfoliation. They have continuously helped in understanding the genetic and developmental mechanisms of degenerative diseases like Alzheimer's and Parkinson's disease. Moreover, the mode of infection of various viruses that can lead to postviral olfactory dysfunction, such as the Zika virus can be monitored through these cells in vitro and their therapeutic development can be fastened.

Endogenous Neural Stem Cell Mediated Oligodendrogenesis in the Adult Mammalian Brain

Oligodendrogenesis is essential for replacing worn-out oligodendrocytes, promoting myelin plasticity, and for myelin repair following a demyelinating injury in the adult mammalian brain. Neural stem cells are an important source of oligodendrocytes in the adult brain; however, there are considerable differences in oligodendrogenesis from neural stem cells residing in different areas of the adult brain. Amongst the distinct niches containing neural stem cells, the subventricular zone lining the lateral ventricles and the subgranular zone in the dentate gyrus of the hippocampus are considered the principle areas of adult neurogenesis. In addition to these areas, radial glia-like cells, which are the precursors of neural stem cells, are found in the lining of the third ventricle, where they are called tanycytes, and in the cerebellum, where they are called Bergmann glia. In this review, we will describe the contribution and regulation of each of these niches in adult oligodendrogenesis.

Human mini brains and spinal cords in a dish: Modeling strategies, current challenges, and prospective advances

Engineered three-dimensional (3D) in vitro and ex vivo neural tissues, also known as "mini brains and spinal cords in a dish," can be derived from different types of human stem cells via several differentiation protocols. In general, human mini brains are micro-scale physiological systems consisting of mixed populations of neural progenitor cells, glial cells, and neurons that may represent key features of human brain anatomy and function. To date, these specialized 3D tissue structures can be characterized into spheroids, organoids, assembloids, organ-on-a-chip and their various combinations based on generation procedures and cellular components. These 3D CNS models incorporate complex cell-cell interactions and play an essential role in bridging the gap between two-dimensional human neuroglial cultures and animal models. Indeed, they provide an innovative platform for disease modeling and therapeutic cell replacement, especially shedding light on the potential to realize personalized medicine for neurological disorders when combined with the revolutionary human induced pluripotent stem cell technology. In this review, we highlight human 3D CNS models developed from a variety of experimental strategies, emphasize their advances and remaining challenges, evaluate their state-of-the-art applications in recapitulating crucial phenotypic aspects of many CNS diseases, and discuss the role of contemporary technologies in the prospective improvement of their composition, consistency, complexity, and maturation.

Sox-positive cell population in the adult cerebellum increases upon tissue degeneration

Adult neurogenesis is well-described in the subventricular and subgranular zones of the mammalian brain. Recent observations that resident glia express stem cell markers in some areas of the brain not traditionally associated with neurogenesis hint to a possible role in tissue repair. The Bergmann glia (BG) population in the cerebellum displays markers and in vitro features associated with neural stem cells (NSC), however the physiological relevance of this phenotypic overlap remains unclear in the absence of established in vivo evidence of tissue regeneration in the adult cerebellum. Here, this BG population was analysed in the adult cerebellum of different species and showed conservation of NSC-associated marker expression including Sox1, Sox2 and Sox9, in chick, primate and mouse cerebellum tissue. NSC-like cells isolated from adult mouse cerebellum showed slower growth when compared to lateral ventricle NSC, as well as differences upon differentiation. In a mouse model of cerebellar degeneration, progressive Purkinje cell loss was linked to cerebellar cortex disorganisation and a significant increase in Sox-positive cells compared to matching controls. These results show that this Sox-positive population responds to cerebellar tissue disruption, suggesting it may represent a mobilisable cellular resource for targeted strategies to promote tissue repair.

Live Imaging Reveals Cerebellar Neural Stem Cell Dynamics and the Role of VNUT in Lineage Progression

Little is known about the intrinsic specification of postnatal cerebellar neural stem cells (NSCs) and to what extent they depend on information from their local niche. Here, we have used an adapted cell preparation of isolated postnatal NSCs and live imaging to demonstrate that cerebellar progenitors maintain their neurogenic nature by displaying hallmarks of NSCs. Furthermore, by using this preparation, all the cell types produced postnatally in the cerebellum, in similar relative proportions to those observed in vivo, can be monitored. The fact that neurogenesis occurs in such organized manner in the absence of signals from the local environment, suggests that cerebellar lineage progression is to an important extent governed by cell-intrinsic or pre-programmed events. Finally, we took advantage of the absence of the niche to assay the influence of the vesicular nucleotide transporter inhibition, which dramatically reduced the number of NSCs in vitro by promoting their progression toward neurogenesis.

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We present a preparation that allows monitoring the behavior of cerebellar NSCs

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Isolated NSCs maintain their neurogenic nature in absence of niche factors

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The model enables monitoring the three postnatal cerebellar niches simultaneously

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VNUT influences the balance between quiescence and activation of cerebellar NSCs

Generation of cortical neurons through large-scale expanding neuroepithelial stem cell from human pluripotent stem cells

Background

Considerable progress has been made in converting human pluripotent stem cells (hPSCs) into cortical neurons for disease modeling and regenerative medicine. However, these procedures are hard to provide sufficient cells for their applications. Using a combination of small-molecules and growth factors, we previously identified one condition which can rapidly induce hPSCs into neuroepithelial stem cells (NESCs). Here, we developed a scalable suspension culture system, which largely yields high-quality NESC-spheres and subsequent cortical neurons.

Methods

The NESC medium was first optimized, and the suspension culture system was then enlarged from plates to stirred bioreactors for large-scale production of NESC-spheres by a stirring speed of 60 rpm. During the expansion, the quality of NESC-spheres was evaluated. The differentiation potential of NESC-spheres into cortical neurons was demonstrated by removing bFGF and two pathway inhibitors from the NESC medium. Cellular immunofluorescence staining, global transcriptome, and single-cell RNA sequencing analysis were used to identify the characteristics, identities, purities, or homogeneities of NESC-spheres or their differentiated cells, respectively.

Results

The optimized culture system is more conducive to large-scale suspension production of NESCs. These largely expanded NESC-spheres maintain unlimited self-renewal ability and NESC state by retaining their uniform sizes, high cell vitalities, and robust expansion abilities. After long-term expansion, NESC-spheres preserve high purity, homogeneity, and normal diploid karyotype. These expanded NESC-spheres on a large scale have strong differentiation potential and effectively produce mature cortical neurons.

Conclusions

We developed a serum-free, defined, and low-cost culture system for large-scale expansion of NESCs in stirred suspension bioreactors. The stable and controllable 3D system supports long-term expansion of high-quality and homogeneous NESC-spheres. These NESC-spheres can be used to efficiently give rise to cortical neurons for cell therapy, disease modeling, and drug screening in future.

In Vitro Recapitulation of Developmental Transitions in Human Neural Stem Cells

During nervous system development, early neuroepithelial stem (NES) cells with a highly polarized morphology and responsiveness to regionalizing morphogens give rise to radial glia (RG) cells, which generate region-specific neurons. Recently, stable neural cell populations reminiscent of NES cells have been obtained from pluripotent stem cells and the fetal human hindbrain. Here, we explore whether these cell populations, similar to their in vivo counterparts, can give rise to neural stem (NS) cells with RG-like properties and whether region-specific NS cells can be generated from NES cells with different regional identities. In vivo RG cells are thought to form from NES cells with the onset of neurogenesis. Therefore, we cultured NES cells temporarily in differentiating conditions. Upon reinitiation of growth factor treatment, cells were found to enter a developmental stage reflecting major characteristics of RG-like NS cells. These NES cell-derived NS cells exhibited a very similar morphology and marker expression as primary NS cells generated from human fetal tissue, indicating that conversion of NES cells into NS cells recapitulates the developmental progression of early NES cells into RG cells observed in vivo. Importantly, NS cells generated from NES cells with different regional identities exhibited stable region-specific transcription factor expression and generated neurons appropriate for their positional identity. Stem Cells 2019;37:1429-1440.

Isolation and Characterization of Cerebellum-Derived Stem Cells in Poststroke Human Brain

There is compelling evidence that the mature central nervous system (CNS) harbors stem cell populations outside conventional neurogenic regions. We previously demonstrated that brain pericytes (PCs) in both mouse and human exhibit multipotency to differentiate into various neural lineages following cerebral ischemia. PCs are found throughout the CNS, including cerebellum, but it remains unclear whether cerebellar PCs also form ischemia-induced multipotent stem cells (iSCs). In this study, we demonstrate that putative iSCs can be isolated from poststroke human cerebellum (cerebellar iSCs [cl-iSCs]). These cl-iSCs exhibited multipotency and differentiated into electrophysiologically active neurons. Neurogenic potential was also confirmed in single-cell suspensions. DNA microarray analysis revealed highly similar gene expression patterns between PCs and cl-iSCs, suggesting PC origin. Global gene expression comparison with cerebral iSCs revealed general similarity, but cl-iSCs differentially expressed certain cerebellum-specific genes. Thus, putative iSCs are present in poststroke cerebellum and possess region-specific traits, suggesting potential capacity to regenerate functional cerebellar neurons following ischemic stroke.

Isolation of Neural Stem Cells from the embryonic mouse hippocampus for in vitro growth or engraftment into a host tissue

For both stem cell research and treatment of the central nervous system disorders, neural stem/progenitor cells (NSPCs) represent an important breakthrough tool. In the expanded stem cell-based therapy use, NSPCs not only provide a powerful cell source for neural cell replacement but a useful model for developmental biology research. Despite numerous approaches were described for isolation of NSPCs from either fetal or adult brain, the main issue remains in extending cell survival following isolation. Here we provide a simple and affordable protocol for making viable NSPCs from the fetal mouse hippocampi, which are capable of maintaining the high viability in a 2D monolayer cell culture or generating 3D neuro-spheroids of cell aggregates. Further, we describe the detailed method for engraftment of embryonic NSPCs onto a host hippocampal tissue for promoting multilinear cell differentiation and maturation within endogenous environment. Our experimental data demonstrate that embryonic NSPCs isolated using this approach show the high viability (above 88%). Within a host tissue, these cells were capable of differentiating to the main neural subpopulations (principal neurons, oligodendrocytes, astroglia). Finally, NSPC-derived neurons demonstrated matured functional properties (electrophysiological activity), becoming functionally integrated into the host hippocampal circuits within a couple of weeks after engraftment.

Recent advances in understanding the mechanisms of cerebellar granule cell development and function and their contribution to behavior

The cerebellum is the focus of an emergent series of debates because its circuitry is now thought to encode an unexpected level of functional diversity. The flexibility that is built into the cerebellar circuit allows it to participate not only in motor behaviors involving coordination, learning, and balance but also in non-motor behaviors such as cognition, emotion, and spatial navigation. In accordance with the cerebellum’s diverse functional roles, when these circuits are altered because of disease or injury, the behavioral outcomes range from neurological conditions such as ataxia, dystonia, and tremor to neuropsychiatric conditions, including autism spectrum disorders, schizophrenia, and attention-deficit/hyperactivity disorder. Two major questions arise: what types of cells mediate these normal and abnormal processes, and how might they accomplish these seemingly disparate functions? The tiny but numerous cerebellar granule cells may hold answers to these questions. Here, we discuss recent advances in understanding how the granule cell lineage arises in the embryo and how a stem cell niche that replenishes granule cells influences wiring when the postnatal cerebellum is injured. We discuss how precisely coordinated developmental programs, gene expression patterns, and epigenetic mechanisms determine the formation of synapses that integrate multi-modal inputs onto single granule cells. These data lead us to consider how granule cell synaptic heterogeneity promotes sensorimotor and non-sensorimotor signals in behaving animals. We discuss evidence that granule cells use ultrafast neurotransmission that can operate at kilohertz frequencies. Together, these data inspire an emerging view for how granule cells contribute to the shaping of complex animal behaviors.

Neurogenesis in the postnatal cerebellum after injury

The cerebellum plays major role in motor coordination and learning. It contains half of the neurons in the brain. Thus, deciphering the mechanisms by which cerebellar neurons are generated is essential to understand the cerebellar functions and the pathologies associated with it. In a recent study, Wojcinski et al. (2017) by using in vivo Cre/loxP technologies reveal that Nestin-expressing progenitors repopulated the external granular cell layer after injury. Depletion of postnatal external granular cell layer is not sufficient to induce motor behavior defects in adults, as the cerebellum recovers these neurons. Strikingly, Nestin-expressing progenitors differentiate into granule cell precursors and mature granule neurons after ablation of perinatal external granular layer, either by irradiation or by genetic ablation. This work identified a novel role of Nestin-expressing progenitors in the cerebellar microenvironment during development, and revealed that extracellular signals can convert specified progenitors into multipotent stem cells. Here, we discuss the findings from this study, and evaluate recent advances in our understanding of the cerebellar neurogenesis.

Cerebellar granule cell replenishment postinjury by adaptive reprogramming of Nestin+ progenitors

Regeneration of several organs involves adaptive reprogramming of progenitors, however, the intrinsic capacity of the developing brain to replenish lost cells remains largely unknown. In this study, we discovered that the developing cerebellum has unappreciated progenitor plasticity, since it undergoes near full growth and functional recovery following acute depletion of granule cells, the most plentiful neuron population in the brain. We demonstrate that following postnatal ablation of granule cell progenitors, Nestin-expressing progenitors (NEPs) specified during mid-embryogenesis to produce astroglia and interneurons, switch their fate and generate granule neurons in mice. Moreover, Hedgehog-signaling in two NEP populations is crucial not only for the compensatory replenishment of granule neurons but also to scale interneuron and astrocyte numbers. Thus we provide insights into the mechanisms underlying robustness of circuit formation in the cerebellum, and speculate that adaptive reprogramming of progenitors in other brain regions plays a greater role than appreciated in developmental regeneration.

Neurogenesis from Sox2 expressing cells in the adult cerebellar cortex

We identified a rare undifferentiated cell population that is intermingled with the Bergmann glia of the adult murine cerebellar cortex, expresses the stem cell markers Sox2 and Nestin, and lacks markers of glial or neuronal differentiation. Interestingly, such Sox2⁺ S100^- cells of the adult cerebellum expanded after adequate physiological stimuli in mice (exercise), and Sox2⁺ precursors acquired positivity for the neuronal marker NeuN over time and integrated into cellular networks. In human patients, SOX2⁺ S100^- cells similarly increased in number after relevant pathological insults (infarcts), suggesting a similar expansion of cells that lack terminal glial differentiation.

SVCT2 Is Expressed by Cerebellar Precursor Cells, Which Differentiate into Neurons in Response to Ascorbic Acid

Ascorbic acid (AA) is a known antioxidant that participates in a wide range of processes, including stem cell differentiation. It enters the cell through the sodium-ascorbate co-transporter SVCT2, which is mainly expressed by neurons in the adult brain. Here, we have characterized SVCT2 expression in the postnatal cerebellum in situ, a model used for studying neurogenesis, and have identified its expression in granular precursor cells and mature neurons. We have also detected SVCT2 expression in the cerebellar cell line C17.2 and in postnatal cerebellum-derived neurospheres in vitro and have identified a tight relationship between SVCT2 expression and that of the stem cell-like marker nestin. AA supplementation potentiates the neuronal phenotype in cerebellar neural stem cells by increasing the expression of the neuronal marker β III tubulin. Stable over-expression of SVCT2 in C17.2 cells enhances β III tubulin expression, but it also increases cell death, suggesting that AA transporter levels must be finely tuned during neural stem cell differentiation.

Consensus Paper: Cerebellar Development

The development of the mammalian cerebellum is orchestrated by both cell-autonomous programs and inductive environmental influences. Here, we describe the main processes of cerebellar ontogenesis, highlighting the neurogenic strategies used by developing progenitors, the genetic programs involved in cell fate specification, the progressive changes of structural organization, and some of the better-known abnormalities associated with developmental disorders of the cerebellum.

Medulloblastoma: Tumor Biology and Relevance to Treatment and Prognosis Paradigm

Medulloblastoma is a malignant embryonic brain tumor arising in the posterior fossa and typically occurring in pediatric patients. Current multimodal treatment regimes have significantly improved the survival rates; however, a marked heterogeneity in therapy response is observed, and one third of all patients die within 5 years after diagnosis. Large-scale genetic and transcriptome analysis revealed four medulloblastoma subgroups (WNT, SHH, Group 3, and Group 4) associated with different demographic parameters, tumor manifestation, and clinical behavior. Future treatment protocols will integrate molecular classification schemes to evaluate subgroup-specific intensification or de-escalation of adjuvant therapies aimed to increase tumor control and reduce iatrogenic induced morbidity. Furthermore, the identification of genetic drivers allows assessing target therapies in order to increase the chemotherapeutic armamentarium. This review highlights the biology behind the current classification system and elucidates relevant aspects of the disease influencing forthcoming clinical trials.

Physiological, pathological, and engineered cell identity reprogramming in the central nervous system

Multipotent neural stem cells persist in restricted regions of the adult mammalian central nervous system. These proliferative cells differentiate into diverse neuron subtypes to maintain neural homeostasis. This endogenous process can be reprogrammed as a compensatory response to physiological cues, traumatic injury, and neurodegeneration. In addition to innate neurogenesis, recent research has demonstrated that new neurons can be engineered via cell identity reprogramming in non-neurogenic regions of the adult central nervous system. A comprehensive understanding of these reprogramming mechanisms will be essential to the development of therapeutic neural regeneration strategies that aim to improve functional recovery after injury and neurodegeneration. WIREs Dev Biol 2016, 5:499-517. doi: 10.1002/wdev.234 For further resources related to this article, please visit the WIREs website.

Control of adult neurogenesis by programmed cell death in the mammalian brain

The presence of neural stem cells (NSCs) and the production of new neurons in the adult brain have received great attention from scientists and the public because of implications to brain plasticity and their potential use for treating currently incurable brain diseases. Adult neurogenesis is controlled at multiple levels, including proliferation, differentiation, migration, and programmed cell death (PCD). Among these, PCD is the last and most prominent process for regulating the final number of mature neurons integrated into neural circuits. PCD can be classified into apoptosis, necrosis, and autophagic cell death and emerging evidence suggests that all three may be important modes of cell death in neural stem/progenitor cells. However, the molecular mechanisms that regulate PCD and thereby impact the intricate balance between self-renewal, proliferation, and differentiation during adult neurogenesis are not well understood. In this comprehensive review, we focus on the extent, mechanism, and biological significance of PCD for the control of adult neurogenesis in the mammalian brain. The role of intrinsic and extrinsic factors in the regulation of PCD at the molecular and systems levels is also discussed. Adult neurogenesis is a dynamic process, and the signals for differentiation, proliferation, and death of neural progenitor/stem cells are closely interrelated. A better understanding of how adult neurogenesis is influenced by PCD will help lead to important insights relevant to brain health and diseases.

Experimental neurotransplantation treatment for hereditary cerebellar ataxias

Hereditary cerebellar degenerations are a heterogeneous group of diseases often having a detrimental impact on patients’ quality of life. Unfortunately, no sufficiently effective causal therapy is available for human patients at present. There are several therapies that have been shown to affect the pathogenetic process and thereby to delay the progress of the disease in mouse models of cerebellar ataxias. The second experimental therapeutic approach for hereditary cerebellar ataxias is neurotransplantation. Grafted cells might provide an effect via delivery of a scarce neurotransmitter, substitution of lost cells if functionally integrated and rescue or trophic support of degenerating cells. The results of cerebellar transplantation research over the past 30 years are reviewed here and potential benefits and limitations of neurotransplantation therapy are discussed.

Heterogeneity and Bipotency of Astroglial-Like Cerebellar Progenitors along the Interneuron and Glial Lineages

Cerebellar GABAergic interneurons in mouse comprise multiple subsets of morphologically and neurochemically distinct phenotypes located at strategic nodes of cerebellar local circuits. These cells are produced by common progenitors deriving from the ventricular epithelium during embryogenesis and from the prospective white matter (PWM) during postnatal development. However, it is not clear whether these progenitors are also shared by other cerebellar lineages and whether germinative sites different from the PWM originate inhibitory interneurons. Indeed, the postnatal cerebellum hosts another germinal site along the Purkinje cell layer (PCL), in which Bergmann glia are generated up to first the postnatal weeks, which was proposed to be neurogenic. Both PCL and PWM comprise precursors displaying traits of juvenile astroglia and neural stem cell markers. First, we examine the proliferative and fate potential of these niches, showing that different proliferative dynamics regulate progenitor amplification at these sites. In addition, PCL and PWM differ in the generated progeny. GABAergic interneurons are produced exclusively by PWM astroglial-like progenitors, whereas PCL precursors produce only astrocytes. Finally, through in vitro, ex vivo, and in vivo clonal analyses we provide evidence that the postnatal PWM hosts a bipotent progenitor that gives rise to both interneurons and white matter astrocytes.

Cell replacement therapy: lessons from teleost fish

Many disorders of the CNS are characterized by a massive loss of neurons. A promising therapeutic strategy to cure such conditions is based on the activation of endogenous stem cells. Implementation of this strategy will benefit from a better understanding of stem cell dynamics and the local CNS microenvironment in regeneration-competent vertebrate model systems. Using a spinal cord injury paradigm in zebrafish larvae, Briona and Dorsky (2014) have provided evidence for the existence of two distinct neural stem cell populations. One population has the characteristics of radial glia and expresses the homeobox transcription factor Dbx. The other lacks Dbx but expresses Olig2. These results are placed in the context of other studies that also support the notion of heterogeneity of adult stem cells in the CNS. The implication that differences among stem cell populations, in combination with specific factors from the local cellular microenvironment, might have a decisive impact on the fate choices of the new cells, is discussed. Reviewed evidence suggests that rather few modifications in the signaling pathways involved in the control of stem cell behavior have led, in the course of evolution, to the pronounced differences between mammals and regeneration-competent organisms. As a consequence, rather minor pharmacological manipulations may be sufficient to reactivate the hidden neurogenic potential of the mammalian CNS, and thus make it available for therapeutic applications.

Endogenous cerebellar neurogenesis in adult mice with progressive ataxia

OBJECTIVE

Transplanting exogenous neuronal progenitors to replace damaged neurons in the adult brain following injury or neurodegenerative disorders and achieve functional amelioration is a realistic goal. However, studies so far have rarely taken into consideration the preexisting inflammation triggered by the disease process that could hamper the effectiveness of transplanted cells. Here, we examined the fate and long-term consequences of human cerebellar granule neuron precursors (GNP) transplanted into the cerebellum of Harlequin mice, an adult model of progressive cerebellar degeneration with early-onset microgliosis.

METHODS

Human embryonic stem cell-derived progenitors expressing Atoh1, a transcription factor key to GNP specification, were generated in vitro and stereotaxically transplanted into the cerebellum of preataxic Harlequin mice. The histological and functional impact of these transplants was followed using immunolabeling and Rotarod analysis.

RESULTS

Although transplanted GNPs did not survive beyond a few weeks, they triggered the proliferation of endogenous nestin-positive precursors in the leptomeninges that crossed the molecular layer and differentiated into mature neurons. These phenomena were accompanied by the preservation of the granule and Purkinje cell layers and delayed ataxic changes. In vitro neurosphere generation confirmed the enhanced neurogenic potential of the cerebellar leptomeninges of Harlequin mice transplanted with exogenous GNPs.

INTERPRETATION

The cerebellar leptomeninges of adult mice contain an endogenous neurogenic niche that can be stimulated to yield mature neurons from an as-yet unidentified population of progenitors. The transplantation of human GNPs not only stimulates this neurogenesis, but, despite the potentially hostile environment, leads to neuroprotection and functional amelioration.

Enteric neural progenitors are more efficient than brain-derived progenitors at generating neurons in the colon

Gut motility disorders can result from an absent, damaged, or dysfunctional enteric nervous system (ENS). Cell therapy is an exciting prospect to treat these enteric neuropathies and restore gut motility. Previous studies have examined a variety of sources of stem/progenitor cells, but the ability of different sources of cells to generate enteric neurons has not been directly compared. It is important to identify the source of stem/progenitor cells that is best at colonizing the bowel and generating neurons following transplantation. The aim of this study was to compare the ability of central nervous system (CNS) progenitors and ENS progenitors to colonize the colon and differentiate into neurons. Genetically labeled CNS- and ENS-derived progenitors were cocultured with aneural explants of embryonic mouse colon for 1 or 2.5 wk to assess their migratory, proliferative, and differentiation capacities, and survival, in the embryonic gut environment. Both progenitor cell populations were transplanted in the postnatal colon of mice in vivo for 4 wk before they were analyzed for migration and differentiation using immunohistochemistry. ENS-derived progenitors migrated further than CNS-derived cells in both embryonic and postnatal gut environments. ENS-derived progenitors also gave rise to more neurons than their CNS-derived counterparts. Furthermore, neurons derived from ENS progenitors clustered together in ganglia, whereas CNS-derived neurons were mostly solitary. We conclude that, within the gut environment, ENS-derived progenitors show superior migration, proliferation, and neuronal differentiation compared with CNS progenitors.

Transit amplification in the amniote cerebellum evolved via a heterochronic shift in NeuroD1 expression

The cerebellum has evolved elaborate foliation in the amniote lineage as a consequence of extensive Atoh1-mediated transit amplification in an external germinal layer (EGL) comprising granule cell precursors. To explore the evolutionary origin of this layer, we have examined the molecular geography of cerebellar development throughout the life cycle of Xenopus laevis. At metamorphic stages Xenopus displays a superficial granule cell layer that is not proliferative and expresses both Atoh1 and NeuroD1, a marker of postmitotic cerebellar granule cells. Premature misexpression of NeuroD1 in chick partially recapitulates the amphibian condition by suppressing transit amplification. However, unlike in the amphibian, granule cells fail to enter the EGL. Furthermore, misexpression of NeuroD1 once the EGL is established both triggers radial migration and downregulates Atoh1. These results show that the evolution of transit amplification in the EGL required adaptation of NeuroD1, both in the timing of its expression and in its regulatory function, with respect to Atoh1.

Long-lasting anxiolytic effect of neural precursor cells freshly prepared but not neurosphere-derived cell transplantation in newborn rats

BACKGROUND

The GABAergic system plays an important role in modulating levels of anxiety. When transplanted into the brain, precursor cells from the medial ganglionic eminence (MGE) have the ability to differentiate into GABAergic interneurons and modify the inhibitory tone in the host brain. Currently, two methods have been reported for obtaining MGE precursor cells for transplantation: fresh and neurosphere dissociated cells. Here, we investigated the effects generated by transplantation of the two types of cell preparations on anxiety behavior in rats.

RESULTS

We transplanted freshly dissociated or neurosphere dissociated cells into the neonate brain of male rats on postnatal (PN) day 2-3. At early adulthood (PN 62-63), transplanted animals were tested in the Elevated Plus Maze (EPM). To verify the differentiation and migration pattern of the transplanted cells in vitro and in vivo, we performed immunohistochemistry for GFP and several interneuron-specific markers: neuropeptide Y (NPY), parvalbumin (PV) and calretinin (CR). Cells from both types of preparations expressed these interneuronal markers. However, an anxiolytic effect on behavior in the EPM was observed in animals that received the MGE-derived freshly dissociated cells but not in those that received the neurosphere dissociated cells.

CONCLUSION

Our results suggest a long-lasting anxiolytic effect of transplanted freshly dissociated cells that reinforces the inhibitory function of the GABAergic neuronal circuitry in the hippocampus related to anxiety-like behavior in rats.

Cerebellar stem cells do not produce neurons and astrocytes in adult mouse

Although previous studies implied that cerebellar stem cells exist in some adult mammals, little is known about whether these stem cells can produce new neurons and astrocytes. In this study by bromodeoxyuridine (BrdU) intraperitoneal (i.p.) injection, we found that there are abundant BrdU(+) cells in adult mouse cerebellum, and their quantity and density decreases significantly over time. We also found cell proliferation rate is diversified in different cerebellar regions. Among these BrdU(+) cells, very few are mash1(+) or nestin(+) stem cells, and the vast majority of cerebellar stem cells are quiescent. Data obtained by in vivo retrovirus injection indicate that stem cells do not produce neurons and astrocytes in adult mouse cerebellum. Instead, some cells labeled by retrovirus are Iba1(+) microglia. These results indicate that very few stem cells exist in adult mouse cerebellum, and none of these stem cells contribute to neurogenesis and astrogenesis under physiological condition.

Independently specified Atoh1 domains define novel developmental compartments in rhombomere 1

The rhombic lip gives rise to neuronal populations that contribute to cerebellar, proprioceptive and interoceptive networks. Cell production depends on the expression of the basic helix-loop-helix (bHLH) transcription factor Atoh1. In rhombomere 1, Atoh1-positive cells give rise to both cerebellar neurons and extra-cerebellar nuclei in ventral hindbrain. The origin of this cellular diversity has previously been attributed to temporal signals rather than spatial patterning. Here, we show that in both chick and mouse the cerebellar Atoh1 precursor pool is partitioned into initially cryptic spatial domains that reflect the activity of two different organisers: an isthmic Atoh1 domain, which gives rise to isthmic nuclei, and the rhombic lip, which generates deep cerebellar nuclei and granule cells. We use a combination of in vitro explant culture, genetic fate mapping and gene overexpression and knockdown to explore the role of isthmic signalling in patterning these domains. We show that an FGF-dependent isthmic Atoh1 domain is the origin of distinct populations of Lhx9-positive neurons in the extra-cerebellar isthmic nuclei. In the cerebellum, ectopic FGF induces proliferation while blockade reduces the length of the cerebellar rhombic lip. FGF signalling is not required for the specification of cerebellar cell types from the rhombic lip and its upregulation inhibits their production. This suggests that although the isthmus regulates the size of the cerebellar anlage, the downregulation of isthmic FGF signals is required for induction of rhombic lip-derived cerebellar neurons.

Comparative human and rat "neurosphere assay" for developmental neurotoxicity testing

The developing nervous system is highly vulnerable to the adverse effects of chemical agents. Currently, there is an increasing need for testing and regulating chemical compounds in general use and, due to the lack of available data, to identify those which are developmental neurotoxicants. In this context, alternative testing strategies are needed in order to allow fast and cost-efficient screening and to reduce the number of animal experiments usually required. In this unit we present an in vitro three-dimensional model for developmental neurotoxicity screening based on human and rat neural progenitor cells. This model enables the detection of disturbances in basic processes of brain development, such as proliferation, migration, differentiation and apoptosis, and allows the distinction of these specific disturbances from general cytotoxicity. Furthermore, the comparison of human and rat data provides useful insights into species differences for toxicodynamics of compounds contributing to human risk assessment of developmental neurotoxicants.

The Purkinje neuron acts as a central regulator of spatially and functionally distinct cerebellar precursors

The prospective white matter (PWM) in the nascent cerebellum contains a transient germinal compartment that produces all postnatally born GABAergic inhibitory interneurons and astrocytes. However, little is known about the molecular identity and developmental potential of resident progenitors or key regulatory niche signals. Here, we show that neural stem-cell-like primary progenitors (Tnc(YFP-low) CD133(+)) generate intermediate astrocyte (Tnc(YFP-low) CD15(+)) precursors and GABAergic transient amplifying (Ptf1a(+)) cells. Interestingly, these lineally related but functionally divergent progenitors commonly respond to Sonic hedgehog (Shh), and blockade of reception in TNC(YFP-low) cells attenuates proliferation in the PWM, reducing both intermediate progenitor classes. Furthermore, we show that Shh produced from distant Purkinje neurons maintains the PWM niche independently of its classical role in regulating granule cell precursor proliferation. Our results indicate that Purkinje neurons maintain a bidirectional signaling axis, driving the production of spatially and functionally opposed inhibitory and excitatory interneurons important for motor learning and cognition.

Unconventional Neurogenic Niches and Neurogenesis Modulation by Vitamins

Although the generation of new neurons occurs in adult mammals, it has been classically described in two defined regions of the brain denominated neurogenic niches: the subventricular zone of the lateral ventricles and the subgranular zone of the dentate gyrus. In these regions, neural stem cells give rise to new neurons and glia, which functionally integrate into the existing circuits under physiological conditions. However, accumulating evidence indicates the presence of neurogenic potential in other brain regions, from which multipotent precursors can be isolated and differentiated in vitro. In some of these regions, neuron generation occurs at low levels; however, the addition of growth factors, hormones or other signaling molecules increases the proliferation and differentiation of precursor cells. In addition, vitamins, which are micronutrients necessary for normal brain development, and whose deficiency produces neurological impairments, have a regulatory effect on neural stem cells in vitro and in vivo. In the present review, we will describe the progress that has been achieved in determining the neurogenic potential in other regions, known as unconventional niches, as well as the characteristics of the neural stem cells described for each region. Finally, we will revisit the roles of commonly known vitamins as modulators of precursor cell proliferation and differentiation, and their role in the complex and tight molecular signaling that impacts these neurogenic niches.

microRNA-17-92 cluster is a direct Nanog target and controls neural stem cell through Trp53inp1

The transcription factor Nanog plays a critical role in the self-renewal of embryonic stem cells as well as in neural stem cells (NSCs). microRNAs (miRNAs) are also involved in stemness regulation. However, the miRNA network downstream of Nanog is still poorly understood. High-throughput screening of miRNA expression profiles in response to modulated levels of Nanog in postnatal NSCs identifies miR-17-92 cluster as a direct target of Nanog. Nanog controls miR-17-92 cluster by binding to the upstream regulatory region and maintaining high levels of transcription in NSCs, whereas Nanog/promoter association and cluster miRNAs expression are lost alongside differentiation. The two miR-17 family members of miR-17-92 cluster, namely miR-17 and miR-20a, target Trp53inp1, a downstream component of p53 pathway. To support a functional role, the presence of miR-17/20a or the loss of Trp53inp1 is required for the Nanog-induced enhancement of self-renewal of NSCs. We unveil an arm of the Nanog/p53 pathway, which regulates stemness in postnatal NSCs, wherein Nanog counteracts p53 signals through miR-17/20a-mediated repression of Trp53inp1.

Direct control of the miRNA-17/92 cluster enables Nanog to restrain p53 activity and thus to maintain pluripotency in neural stem cells.

Origin, lineage and function of cerebellar glia

The glial cells of the cerebellum, and particularly astrocytes and oligodendrocytes, are characterized by a remarkable phenotypic variety, in which highly peculiar morphological features are associated with specific functional features, unique among the glial cells of the entire CNS. Here, we provide a critical report about the present knowledge of the development of cerebellar glia, including lineage relationships between cerebellar neurons, astrocytes and oligodendrocytes, the origins and the genesis of the repertoire of glial types, and the processes underlying their acquisition of mature morphological and functional traits. In parallel, we describe and discuss some fundamental roles played by specific categories of glial cells during cerebellar development. In particular, we propose that Bergmann glia exerts a crucial scaffolding activity that, together with the organizing function of Purkinje cells, is necessary to achieve the normal pattern of foliation and layering of the cerebellar cortex. Moreover, we discuss some of the functional tasks of cerebellar astrocytes and oligodendrocytes that are distinctive of cerebellar glia throughout the CNS. Notably, we report about the regulation of synaptic signalling in the molecular and granular layer mediated by Bergmann glia and parenchymal astrocytes, and the functional interaction between oligodendrocyte precursor cells and neurons. On the whole, this review provides an extensive overview of the available literature and some novel insights about the origin and differentiation of the variety of cerebellar glial cells and their function in the developing and mature cerebellum.

Dynamic Activity of miR-125b and miR-93 during Murine Neural Stem Cell Differentiation In Vitro and in the Subventricular Zone Neurogenic Niche

Several microRNAs (miRNAs) that are either specifically enriched or highly expressed in neurons and glia have been described, but the identification of miRNAs modulating neural stem cell (NSC) biology remains elusive. In this study, we exploited high throughput miRNA expression profiling to identify candidate miRNAs enriched in NSC/early progenitors derived from the murine subventricular zone (SVZ). Then, we used lentiviral miRNA sensor vectors (LV.miRT) to monitor the activity of shortlisted miRNAs with cellular and temporal resolution during NSC differentiation, taking advantage of in vitro and in vivo models that recapitulate physiological neurogenesis and gliogenesis and using known neuronal- and glial-specific miRNAs as reference. The LV.miRT platform allowed us monitoring endogenous miRNA activity in low represented cell populations within a bulk culture or within the complexity of CNS tissue, with high sensitivity and specificity. In this way we validated and extended previous results on the neuronal-specific miR-124 and the astroglial-specific miR-23a. Importantly, we describe for the first time a cell type- and differentiation stage-specific modulation of miR-93 and miR-125b in SVZ-derived NSC cultures and in the SVZ neurogenic niche in vivo, suggesting key roles of these miRNAs in regulating NSC function.

Neurovascular signals suggest a propagation mechanism for endogenous stem cell activation along blood vessels

Stem cell – based therapies for central nervous system disorders are intensely pursued. Such approaches can be divided into two categories: Transplantation-based, and those that aim to pharmacologically target the endogenous stem cell population in the tissue. Endogenous stem cell – based strategies avoid the problem of immune incompatibility between the host and the grafted cells. They also avoid the placement of a large amount of cells in confined areas, a manipulation which alters the characteristics of the neurovascular microenvironment. We show here that massive pharmacological activation (increase in cell numbers) of the endogenous neural stem cell population in the adult rodent brain maintains the cytoarchitecture of the neurovascular niche. Distances between adjacent stem cells (identified by expression of Hes3) are maintained above a minimum. Hes3+ cells maintain their physical association with blood vessels. These results also suggest a mechanism by which the activation signal from the lateral ventricle can be propagated to areas a long distance away from the lateral ventricles, through autocrine/paracrine actions between adjacent Hes3+ cells, along blood vessels. Finally, powerful effects of angiopoietin 2 on Hes3+ cells help explain the prevalence of proliferating endogenous neural stem cells close to the subventricular zone (an area of high angiopoietin 2 concentration) and the quiescent state of stem cells away from the ventricles and their tight physical association with blood vessels (which express high levels of angiopoietin 1, a cytokine that opposes angiopoietin 2 functions).

Fast, potent pharmacological expansion of endogenous hes3+/sox2+ cells in the adult mouse and rat hippocampus

The adult hippocampus is involved in learning and memory. As a consequence, it is a brain region of remarkable plasticity. This plasticity exhibits itself both as cellular changes and neurogenesis. For neurogenesis to occur, a population of local stem cells and progenitor cells is maintained in the adult brain and these are able to proliferate and differentiate into neurons which contribute to the hippocampal circuitry. There is much interest in understanding the role of immature cells in the hippocampus, in relation to learning and memory. Methods and mechanisms that increase the numbers of these cells will be valuable in this research field. We show here that single injections of soluble factors into the lateral ventricle of adult rats and mice induces the rapid (within one week) increase in the number of putative stem cells/progenitor cells in the hippocampus. The established progenitor marker Sox2 together with the more recently established marker Hes3, were used to quantify the manipulation of the Sox2/Hes3 double-positive cell population. We report that in both adult rodent species, Sox2+/Hes3+ cell numbers can be increased within one week. The most prominent increase was observed in the hilus of the dentate gyrus. This study presents a fast, pharmacological method to manipulate the numbers of endogenous putative stem cells/progenitor cells. This method may be easily modified to alter the degree of activation (e.g. by the use of osmotic pumps for delivery, or by repeat injections through implanted cannulas), in order to be best adapted to different paradigms of research (neurodegenerative disease, neuroprotection, learning, memory, plasticity, etc).

Postnatal neural precursor cell regions in the rostral subventricular zone, hippocampal subgranular zone and cerebellum of the dog (Canis lupus familiaris)

Identification of neural stem and progenitor cells (NPCs) in vitro and in vivo is essential to the use of developmental and disease models of neurogenesis. The dog is a valuable large animal model for multiple neurodegenerative diseases and is more closely matched to humans than rodents with respect to brain organization and complexity. It is therefore important to determine whether immunohistochemical markers associated with NPCs in humans and rodents are also appropriate for the dog. The NPC markers CD15, CD133, nestin, GFAP and phosphacan (DSD-1) were evaluated in situ in the canine rostral telencephalon, hippocampal dentate gyrus, and cerebellum at different postnatal time-points. Positive staining results were interpreted in the context of region and cellular morphology. Our results showed that neurospheres and cells within the rostral subventricular zone (SVZ), dentate gyrus subgranular zone (SGZ), and white matter tracts of the cerebellum were immunopositive for CD15, nestin and GFAP. Neurospheres and the cerebellum were immunonegative for CD133, whereas CD133 staining was present in the postnatal rostral SVZ. Anti-phosphacan antibody staining delineated the neurogenic niches of the rostral lateral ventricle SVZ and the hippocampal SGZ. Positive staining for phosphacan was also noted in white matter tracts of the cerebellum and within the Purkinje layer. Our results showed that in the dog these markers were associated with regions shown to be neurogenic in rodents and primates.

The role of stem cells and progenitors in the genesis of medulloblastoma

Cancer results from dysregulation of growth and survival pathways in normal stem cells and progenitors. Identifying the cells from which a tumor arises can facilitate the development of animal models and point to novel targets for therapy. Medulloblastoma is an aggressive tumor of the cerebellum that occurs predominantly in children. Recent genomic studies suggest that medulloblastoma consists of 4 major subgroups, each with distinct mutations and signaling pathway deregulations, and each potentially arising from distinct populations of stem cells and progenitors. Here we review the major types of progenitor cells in the cerebellum and discuss their role in the genesis of medulloblastoma.

Cellular composition characterizing postnatal development and maturation of the mouse brain and spinal cord

The process of development, maturation, and regression in the central nervous system (CNS) are genetically programmed and influenced by environment. Hitherto, most research efforts have focused on either the early development of the CNS or the late changes associated with aging, whereas an important period corresponding to adolescence has been overlooked. In this study, we searched for age-dependent changes in the number of cells that compose the CNS (divided into isocortex, hippocampus, olfactory bulb, cerebellum, 'rest of the brain', and spinal cord) and the pituitary gland in 4-40-week-old C57BL6 mice, using the isotropic fractionator method in combination with neuronal nuclear protein as a marker for neuronal cells. We found that all CNS structures, except for the isocortex, increased in mass in the period of 4-15 weeks. Over the same period, the absolute number of neurons significantly increased in the olfactory bulb and cerebellum while non-neuronal cell numbers increased in the 'rest of the brain' and isocortex. Along with the gain in body length and weight, the pituitary gland also increased in mass and cell number, the latter correlating well with changes of the brain and spinal cord mass. The majority of the age-dependent alterations (e.g., somatic parameters, relative brain mass, number of pituitary cells, and cellular composition of the cerebellum, isocortex, rest of the brain, and spinal cord) occur rapidly between the 4th and 11th postnatal weeks. This period includes murine adolescence, underscoring the significance of this stage in the postnatal development of the mouse CNS.

The role of eNSCs in neurodegenerative disease

Recent progress in biology has shown that many if not all adult tissues contain a population of stem cells. It is believed that these cells are involved in the regeneration of the tissue or organ in which they reside as a response to the natural turnover of differentiated cells or to injury. In the adult mammalian brain, stem cells in the subventricular zone and the dentate gyrus may also play a role in the replacement of neurons. A positive beneficial response to injury does not necessarily require cell replacement. New findings suggest that some populations of endogenous neural stem cells in the central nervous system may have adopted a function different from cell replacement and are involved in the protection of neurons in diverse paradigms of disease and injury. In this article, we will focus on the immature cell populations of the central nervous system and the signal transduction pathways that regulate them which suggest new possibilities for their manipulation in injury and disease.

Genotype-specific differences between mouse CNS stem cell lines expressing frontotemporal dementia mutant or wild type human tau

Stem cell (SC) lines that capture the genetics of disease susceptibility provide new research tools. To assess the utility of mouse central nervous system (CNS) SC-containing neurosphere cultures for studying heritable neurodegenerative disease, we compared neurosphere cultures from transgenic mice that express human tau with the P301L familial frontotemporal dementia (FTD) mutation, rTg(tau(P301L))4510, with those expressing comparable levels of wild type human tau, rTg(tau(wt))21221. rTg(tau(P301L))4510 mice express the human tau(P301L) variant in their forebrains and display cellular, histological, biochemical and behavioral abnormalities similar to those in human FTD, including age-dependent differences in tau phosphorylation that distinguish them from rTg(tau(wt))21221 mice. We compared FTD-hallmark tau phosphorylation in neurospheres from rTg(tau(P301L))4510 mice and from rTg(tau(wt))21221 mice. The tau genotype-specific phosphorylation patterns in neurospheres mimicked those seen in mice, validating use of neurosphere cultures as models for studying tau phosphorylation. Genotype-specific tau phosphorylation was observed in 35 independent cell lines from individual fetuses; tau in rTg(tau(P301L))4510 cultures was hypophosphorylated in comparison with rTg(tau(wt))21221 as was seen in young adult mice. In addition, there were fewer human tau-expressing cells in rTg(tau(P301L))4510 than in rTg(tau(wt))21221 cultures. Following differentiation, neuronal filopodia-spine density was slightly greater in rTg(tau(P301L))4510 than rTg(tau(wt))21221 and control cultures. Together with the recapitulation of genotype-specific phosphorylation patterns, the observation that neurosphere lines maintained their cell line-specific-differences and retained SC characteristics over several passages supports the utility of SC cultures as surrogates for analysis of cellular disease mechanisms.

Distinct neural stem cell populations give rise to disparate brain tumors in response to N-MYC

The proto-oncogene MYCN is mis-expressed in various types of human brain tumors. To clarify how developmental and regional differences influence transformation, we transduced wild-type or mutationally stabilized murine N-myc(T58A) into neural stem cells (NSCs) from perinatal murine cerebellum, brain stem, and forebrain. Transplantation of N-myc(WT) NSCs was insufficient for tumor formation. N-myc(T58A) cerebellar and brain stem NSCs generated medulloblastoma/primitive neuroectodermal tumors, whereas forebrain NSCs developed diffuse glioma. Expression analyses distinguished tumors generated from these different regions, with tumors from embryonic versus postnatal cerebellar NSCs demonstrating Sonic Hedgehog (SHH) dependence and SHH independence, respectively. These differences were regulated in part by the transcription factor SOX9, activated in the SHH subclass of human medulloblastoma. Our results demonstrate context-dependent transformation of NSCs in response to a common oncogenic signal.