Strengths and Limitations of the Neurosphere Culture System

One mouse, two cultures: isolation and culture of adult neural stem cells from the two neurogenic zones of individual mice

The neurosphere assay and the adherent monolayer culture system are valuable tools to determine the potential (proliferation or differentiation) of adult neural stem cells in vitro. These assays can be used to compare the precursor potential of cells isolated from genetically different or differentially treated animals to determine the effects of exogenous factors on neural precursor cell proliferation and differentiation and to generate neural precursor cell lines that can be assayed over continuous passages. The neurosphere assay is traditionally used for the post-hoc identification of stem cells, primarily due to the lack of definitive markers with which they can be isolated from primary tissue and has the major advantage of giving a quick estimate of precursor cell numbers in brain tissue derived from individual animals. Adherent monolayer cultures, in contrast, are not traditionally used to compare proliferation between individual animals, as each culture is generally initiated from the combined tissue of between 5-8 animals. However, they have the major advantage that, unlike neurospheres, they consist of a mostly homogeneous population of precursor cells and are useful for following the differentiation process in single cells. Here, we describe, in detail, the generation of neurosphere cultures and, for the first time, adherent cultures from individual animals. This has many important implications including paired analysis of proliferation and/or differentiation potential in both the subventricular zone (SVZ) and dentate gyrus (DG) of treated or genetically different mouse lines, as well as a significant reduction in animal usage.

Human trabecular meshwork cells exhibit several characteristics of, but are distinct from, adipose-derived mesenchymal stem cells

PURPOSE

To support the growing promise of regenerative medicine in glaucoma, we characterized the similarities and differences between human trabecular meshwork (HTM) cells and human mesenchymal stem cells (hMSCs).

METHODS

HTM cells and hMSCs were phenotypically characterized by flow cytometry. Using quantitative polymerase chain reaction, the expression of myoc, angptl7, sox2, pou5f1, and notch1 was determined in both cell types with and without dexamethasone (Dex). Immunosuppressive behavior of HTM cells and hMSCs was determined using T cells activated with phytohemagglutinin. T-cell proliferation was determined using BrdU incorporation and flow cytometry. Multipotency of HTM cells and hMSCs was determined using adipogenic and osteogenic differentiation media as well as aqueous humor (AH). Alpha-smooth muscle actin (αSMA) expression was determined in HTM cells, hMSCs, and HTM tissue.

RESULTS

Phenotypically, HTM and hMSCs expressed CD73, CD90, CD105, and CD146 but not CD31, CD34, and CD45 and similar sox2, pou5f1, and notch1 expression. Both cell types suppressed T-cell proliferation. However, HTM cells, but not hMSCs, upregulated myoc and angptl7 in response to Dex. Additionally, HTM cells did not differentiate into adipocytes or osteocytes. Culture of hMSCs in 20%, but not 100%, AH potently induced alkaline phosphatase activity. HTM cells in culture possessed uniformly strong expression of αSMA, which contrasted with the limited expression in hMSCs and spatially discrete expression in HTM tissue.

CONCLUSIONS

HTM cells possess a number of important similarities with hMSCs but lack multipotency, one of the defining characteristics of stem cells. Further work is needed to explore the molecular mechanisms and functional implications underlying the phenotypic similarities.

The in-vitro spheroid culture induces a more highly differentiated but tumorigenic population from melanoma cell lines

Cancer stem cells (CSCs) have been identified in various malignancies, and different properties have been examined to characterize CSCs: tumorigenicity in immunocompromised mice, stem cell surface markers, label-retaining properties, and proliferation as nonadherent spheres. This study explored the consistency and efficiency among these methods. Among the melanoma cell lines examined (A375, A875, MUM-2b, and MUM-2c), only A375 and MUM-2c grew as nonadherent spheres and continuously propagated in a defined serum-free medium in vitro. Flow cytometry and immunofluorescence analysis indicated that sphere-derived cells contained a smaller proportion of cells expressing the candidate surface markers of melanoma stem cells such as ABCB5, CD133, CD20 and CD271, and a larger proportion of cells expressing melanocytic differentiation markers such as HMB45 and S100 protein, compared with adherent cells. Surprisingly, the more highly differentiated sphere-derived melanoma cells exhibited increased tumorigenic potential in vivo, as indicated by shorter tumor incubation (A375) and smaller number of cells required to initiate tumor formation (A375 and MUM-2c) compared with those of parental cells. Despite the similarity in histopathological characteristics, the expression profile indicated that xenografts derived from sphere-derived melanoma cells exhibited a more tumorigenic phenotype with respect to the stem or the differentiation markers detected by immunohistochemical analysis. Therefore, sphere formation in nonadherent cultures may not be a preferred surrogate in-vitro method for enriching melanoma stem cells according to candidate markers but may be a favorable condition for activating potential CSCs.

In vitro multilineage differentiation and self-renewal of single pancreatic colony-forming cells from adult C57BL/6 mice

In a previous study we established colony assays suitable for studying murine adult (2-4 months) pancreatic progenitor cells plated in semisolid media containing methylcellulose and extracellular matrix proteins. Using these assays, we found robust in vitro progenitor cell activities (multilineage differentiation and self-renewal) from pancreatic cells of adult mice in the CD-1 outbred background. However, it was not clear whether progenitor cell activities can be detected from inbred mice, a preferred mouse model for various genetic studies. It was also not clear whether a single cell is sufficient to self-renew. Here, we show that fluorescent activated cell sorting pancreatic CD133(+) but not CD133(-) cells from adult C57Bl/6 inbred mice are enriched for progenitor cells that self-renew and give rise to multilineage colonies in vitro. The number of cells in a colony is in proportion to its diameter. Around 60% of single handpicked 3-week-old colonies express trilineage markers, indicating most progenitors are tripotent for ductal, acinar, and endocrine lineage differentiation. Approximately 80% of primary (freshly sorted) colony-forming progenitor cells are capable of giving rise to secondary progenitors in vitro, indicating that a majority of the primary progenitors self-renew. A single cell is sufficient for self-renewal and a Wnt agonist, R-Spondin1, enhances the number of secondary progenitors from the primary progenitors. Together, our pancreatic colony assays allow quantitative analyses of progenitors at a single-cell level from inbred mice. These assays will be useful for elucidating in vitro mechanisms of pancreatic progenitor cell biology.

Ribosomal S6 kinase regulates ischemia-induced progenitor cell proliferation in the adult mouse hippocampus

Ischemia-induced progenitor cell proliferation is a prominent example of the adult mammalian brain's ability to regenerate injured tissue resulting from pathophysiological processes. In order to better understand and exploit the cell signaling mechanisms that regulate ischemia-induced proliferation, we examined the role of the p42/44 mitogen-activated protein kinase (MAPK) cascade effector ribosomal S6 kinase (RSK) in this process. Here, using the endothelin-1 ischemia model in wild type mice, we show that the activated form of RSK is expressed in the progenitor cells of the subgranular zone (SGZ) after intrahippocampal cerebral ischemia. Further, RSK inhibition significantly reduces ischemia-induced SGZ progenitor cell proliferation. Using the neurosphere assay, we also show that both SGZ- and subventricular zone (SVZ)-derived adult neural stem cells (NSC) exhibit a significant reduction in proliferation in the presence of RSK and MAPK inhibitors. Taken together, these data reveal RSK as a regulator of ischemia-induced progenitor cell proliferation, and as such, suggest potential therapeutic value may be gained by specifically targeting the regulation of RSK in the progenitor cell population of the SGZ.

Growing neural stem cells from conventional and nonconventional regions of the adult rodent brain

Recent work demonstrates that central nervous system (CNS) regeneration and tumorigenesis involves populations of stem cells (SCs) resident within the adult brain. However, the mechanisms these normally quiescent cells employ to ensure proper functioning of neural networks, as well as their role in recovery from injury and mitigation of neurodegenerative processes are little understood. These cells reside in regions referred to as "niches" that provide a sustaining environment involving modulatory signals from both the vascular and immune systems. The isolation, maintenance, and differentiation of CNS SCs under defined culture conditions which exclude unknown factors, makes them accessible to treatment by pharmacological or genetic means, thus providing insight into their in vivo behavior. Here we offer detailed information on the methods for generating cultures of CNS SCs from distinct regions of the adult brain and approaches to assess their differentiation potential into neurons, astrocytes, and oligodendrocytes in vitro. This technique yields a homogeneous cell population as a monolayer culture that can be visualized to study individual SCs and their progeny. Furthermore, it can be applied across different animal model systems and clinical samples, being used previously to predict regenerative responses in the damaged adult nervous system.

Does the adult human ciliary body epithelium contain "true" retinal stem cells?

Recent reports of retinal stem cells being present in several locations of the adult eye have sparked great hopes that they may be used to treat the millions of people worldwide who suffer from blindness as a result of retinal disease or injury. A population of proliferative cells derived from the ciliary body epithelium (CE) has been considered one of the prime stem cell candidates, and as such they have received much attention in recent years. However, the true nature of these cells in the adult human eye has still not been fully elucidated, and the stem cell claim has become increasingly controversial in light of new and conflicting reports. In this paper, we will try to answer the question of whether the available evidence is strong enough for the research community to conclude that the adult human CE indeed harbors stem cells.

CSF-1R inhibition alters macrophage polarization and blocks glioma progression

Glioblastoma multiforme (GBM) comprises several molecular subtypes including proneural GBM. Most therapeutic approaches targeting glioma cells have failed. An alternative strategy is to target cells in the glioma microenvironment, such as tumor-associated macrophages and microglia (TAMs). Macrophages depend upon colony stimulating factor (CSF)-1 for differentiation and survival. A CSF-1R inhibitor was used to target TAMs in a mouse proneural GBM model, which dramatically increased survival, and regressed established tumors. CSF-1R blockade additionally slowed intracranial growth of patient-derived glioma xenografts. Surprisingly, TAMs were not depleted in treated mice. Instead, glioma-secreted factors including GM-CSF and IFN-γ facilitated TAM survival in the context of CSF-1R inhibition. Alternatively activated/ M2 macrophage markers decreased in surviving TAMs, consistent with impaired tumor-promoting functions. These gene signatures were associated with enhanced survival in proneural GBM patients. Our results identify TAMs as a promising therapeutic target for proneural gliomas, and establish the translational potential of CSF-1R inhibition for GBM.

Adult neural stem cells from the subventricular zone: a review of the neurosphere assay

The possibility of obtaining large numbers of cells with potential to become functional neurons implies a great advance in regenerative medicine. A source of cells for therapy is the subventricular zone (SVZ) where adult neural stem cells (NSCs) retain the ability to proliferate, self-renew, and differentiate into several mature cell types. The neurosphere assay, a method to isolate, maintain, and expand these cells has been extensively utilized by research groups to analyze the biological properties of aNSCs and to graft into injured brains from animal models. In this review we briefly describe the neurosphere assay and its limitations, the methods to optimize culture conditions, the identity and the morphology of aNSC-derived neurospheres (including new ultrastructural data). The controversy regarding the identity and "stemness" of cells within the neurosphere is revised. The fine morphology of neurospheres, described thoroughly, allows for phenotypical characterization of cells in the neurospheres and may reveal slight changes that indirectly inform about cell integrity, cell damage, or oncogenic transformation. Along this review we largely highlight the critical points that researchers have to keep in mind before extrapolating results or translating experimental transplantation of neurosphere-derived cells to the clinical setting.

Prion replication elicits cytopathic changes in differentiated neurosphere cultures

The molecular mechanisms of prion-induced cytotoxicity remain largely obscure. Currently, only a few cell culture models have exhibited the cytopathic changes associated with prion infection. In this study, we introduced a cell culture model based on differentiated neurosphere cultures isolated from the brains of neonatal prion protein (PrP)-null mice and transgenic mice expressing murine PrP (dNP0 and dNP20 cultures). Upon exposure to mouse Chandler prions, dNP20 cultures supported the de novo formation of abnormal PrP and the resulting infectivity, as assessed by bioassays. Furthermore, this culture was susceptible to various prion strains, including mouse-adapted scrapie, bovine spongiform encephalopathy, and Gerstmann-Sträussler-Scheinker syndrome prions. Importantly, a subset of the cells in the infected culture that was mainly composed of astrocyte lineage cells consistently displayed late-occurring, progressive signs of cytotoxicity as evidenced by morphological alterations, decreased cell viability, and increased lactate dehydrogenase release. These signs of cytotoxicity were not observed in infected dNP0 cultures, suggesting the requirement of endogenous PrP expression for prion-induced cytotoxicity. Degenerated cells positive for glial fibrillary acidic protein accumulated abnormal PrP and exhibited features of apoptotic death as assessed by active caspase-3 and terminal deoxynucleotidyltransferase nick-end staining. Furthermore, caspase inhibition provided partial protection from prion-mediated cell death. These results suggest that differentiated neurosphere cultures can provide an in vitro bioassay for mouse prions and permit the study of the molecular basis for prion-induced cytotoxicity at the cellular level.

Three-dimensional scaffolding to investigate neuronal derivatives of human embryonic stem cells

Access to unlimited numbers of live human neurons derived from stem cells offers unique opportunities for in vitro modeling of neural development, disease-related cellular phenotypes, and drug testing and discovery. However, to develop informative cellular in vitro assays, it is important to consider the relevant in vivo environment of neural tissues. Biomimetic 3D scaffolds are tools to culture human neurons under defined mechanical and physico-chemical properties providing an interconnected porous structure that may potentially enable a higher or more complex organization than traditional two-dimensional monolayer conditions. It is known that even minor variations in the internal geometry and mechanical properties of 3D scaffolds can impact cell behavior including survival, growth, and cell fate choice. In this report, we describe the design and engineering of 3D synthetic polyethylene glycol (PEG)-based and biodegradable gelatin-based scaffolds generated by a free form fabrication technique with precise internal geometry and elastic stiffnesses. We show that human neurons, derived from human embryonic stem (hESC) cells, are able to adhere to these scaffolds and form organoid structures that extend in three dimensions as demonstrated by confocal and electron microscopy. Future refinements of scaffold structure, size and surface chemistries may facilitate long term experiments and designing clinically applicable bioassays.

Restriction of neural precursor ability to respond to Nurr1 by early regional specification

During neural development, spatially regulated expression of specific transcription factors is crucial for central nervous system (CNS) regionalization, generation of neural precursors (NPs) and subsequent differentiation of specific cell types within defined regions. A critical role in dopaminergic differentiation in the midbrain (MB) has been assigned to the transcription factor Nurr1. Nurr1 controls the expression of key genes involved in dopamine (DA) neurotransmission, e.g. tyrosine hydroxylase (TH) and the DA transporter (DAT), and promotes the dopaminergic phenotype in embryonic stem cells. We investigated whether cells derived from different areas of the mouse CNS could be directed to differentiate into dopaminergic neurons in vitro by forced expression of the transcription factor Nurr1. We show that Nurr1 overexpression can promote dopaminergic cell fate specification only in NPs obtained from E13.5 ganglionic eminence (GE) and MB, but not in NPs isolated from E13.5 cortex (CTX) and spinal cord (SC) or from the adult subventricular zone (SVZ). Confirming previous studies, we also show that Nurr1 overexpression can increase the generation of TH-positive neurons in mouse embryonic stem cells. These data show that Nurr1 ability to induce a dopaminergic phenotype becomes restricted during CNS development and is critically dependent on the region of NPs derivation. Our results suggest that the plasticity of NPs and their ability to activate a dopaminergic differentiation program in response to Nurr1 is regulated during early stages of neurogenesis, possibly through mechanisms controlling CNS regionalization.

Cell and tissue microarray technologies for protein and nucleic acid expression profiling

Tissue microarray (TMA) and cell microarray (CMA) are two powerful techniques that allow for the immunophenotypical characterization of hundreds of samples simultaneously. In particular, the CMA approach is particularly useful for immunophenotyping new stem cell lines (e.g., cardiac, neural, mesenchymal) using conventional markers, as well as for testing the specificity and the efficacy of newly developed antibodies. We propose the use of a tissue arrayer not only to perform protein expression profiling by immunohistochemistry but also to carry out molecular genetics studies. In fact, starting with several tissues or cell lines, it is possible to obtain the complete signature of each sample, describing the protein, mRNA and microRNA expression, and DNA mutations, or eventually to analyze the epigenetic processes that control protein regulation. Here we show the results obtained using the Galileo CK4500 TMA platform.

Tumor-initiating properties of breast cancer and melanoma cells in vivo are not invariably reflected by spheroid formation in vitro, but can be increased by long-term culturing as adherent monolayers

Cancer stem cells (CSCs) have been studied intensively in recent years due to their potential importance for understanding neoplastic disease and the design of antitumor therapies. A number of properties attributed to CSCs have been used to define the CSC population, the most important of which is the ability to initiate reproducibly the growth of tumors in vivo. Other assays such as spheroid formation, expression of particular markers and label retention are also used for defining CSCs, although the degree to which these assays invariably reflect the ability to form tumors in vivo remains to be carefully evaluated. Given the importance of correctly defining and isolating CSCs if valid conclusions about their characteristics are to be made, we used syngeneic animal models to compare these different assays. In standard spheroid assays, cell aggregation rather than spheroid growth from single cell suspensions ensued, but aggregation was circumvented by the inclusion of methylcellulose in the medium. Label-retaining subpopulations did not reliably exhibit an enhanced ability to form spheroids and were enriched for senescent cells. Spheroid-forming ability was found to correspond to expression of established CSC markers, although not invariably. Furthermore, spheroid-forming ability was not always reflected in tumor-initiating properties in vivo. Long-term culture of primary mammary tumor cells as adherent monolayers increased their tumor-initiating ability in vivo. This increase was attenuated when the cells were subsequently cultivated as spheroids. Together these data indicate that assays that are widely used to define CSC subpopulations do not invariably reflect tumor-initiating properties in vivo.

Human midbrain precursors activate the expected developmental genetic program and differentiate long-term to functional A9 dopamine neurons in vitro. Enhancement by Bcl-X(L)

Understanding the molecular programs of the generation of human dopaminergic neurons (DAn) from their ventral mesencephalic (VM) precursors is of key importance for basic studies, progress in cell therapy, drug screening and pharmacology in the context of Parkinson's disease. The nature of human DAn precursors in vitro is poorly understood, their properties unstable, and their availability highly limited. Here we present positive evidence that human VM precursors retaining their genuine properties and long-term capacity to generate A9 type Substantia nigra human DAn (hVM1 model cell line) can be propagated in culture. During a one month differentiation, these cells activate all key genes needed to progress from pro-neural and pro-dopaminergic precursors to mature and functional DAn. For the first time, we demonstrate that gene cascades are correctly activated during differentiation, resulting in the generation of mature DAn. These DAn have morphological and functional properties undistinguishable from those generated by VM primary neuronal cultures. In addition, we have found that the forced expression of Bcl-X(L) induces an increase in the expression of key developmental genes (MSX1, NGN2), maintenance of PITX3 expression temporal profile, and also enhances genes involved in DAn long-term function, maintenance and survival (EN1, LMX1B, NURR1 and PITX3). As a result, Bcl-X(L) anticipates and enhances DAn generation.

A brain aggregate model gives new insights into the pathobiology and treatment of prion diseases

Brain aggregates (BrnAggs) derived from fetal mouse brains contain mature neurons and glial cells. We determined that BrnAggs are consistently infected with Rocky Mountain Laboratory scrapie strain prions and produce increasing levels of the pathogenic form of the prion protein (PrP). Their abundant dendrites undergo degeneration shortly after prion infection. Treatment of prion-infected BrnAggs with drugs, such as a γ-secretase inhibitors and quinacrine (Qa), which stop PrP formation and dendritic degeneration, mirrors the results from rodent studies. Because PrP is trafficked into lysosomes by endocytosis and autophagosomes by phagocytosis in neurons of prion strain-infected BrnAggs, we studied the effects of drugs that modulate subcellular trafficking. Rapamycin (Rap), which activates autophagy, markedly increased light-chain 3-II (LC3-II)-positive autophagosomes and cathepsin D-positive lysosomes in BrnAggs but could not eliminate the intracellular PrP within them. Adding Qa to Rap markedly reduced the number of LC3-II-positive autolysosomes. Rap + Qa created a competition between Rap increasing and Qa decreasing LC3-II. Rapamycin + Qa decreased total PrP by 56% compared with that of Qa alone, which reduced PrP by 37% relative to Rap alone. We conclude that the decrease was dominated by the ability of Qa to decrease the formation of PrP. Therefore, BrnAggs provide an efficient in vitro tool for screening drug therapies and studying the complex biology of prions.

Head and neck cancer stem cells

Most cancers contain a small sub-population of cells that are endowed with self-renewal, multipotency, and a unique potential for tumor initiation. These properties are considered hallmarks of cancer stem cells. Here, we provide an overview of the field of cancer stem cells with a focus on head and neck cancers. Cancer stem cells are located in the invasive fronts of head and neck squamous cell carcinomas (HNSCC) close to blood vessels (perivascular niche). Endothelial cell-initiated signaling events are critical for the survival and self-renewal of these stem cells. Markers such as aldehyde dehydrogenase (ALDH), CD133, and CD44 have been successfully used to identify highly tumorigenic cancer stem cells in HNSCC. This review briefly describes the orosphere assay, a method for in vitro culture of undifferentiated head and neck cancer stem cells under low attachment conditions. Notably, recent evidence suggests that cancer stem cells are exquisitely resistant to conventional therapy and are the "drivers" of local recurrence and metastatic spread. The emerging understanding of the role of cancer stem cells in the pathobiology of head and neck squamous cell carcinomas might have a profound impact on the treatment paradigms for this malignancy.

Forkhead family transcription factor FoxO and neural differentiation

The Forkhead Box subgroup O (FoxO) transcription factor family is one of the most important downstream targets of the phosphatidylinositol 3-kinase/protein kinase B signaling pathway playing an important role in many biological functions including transcriptional regulation of cellular differentiation. Neuronal differentiation is a complex process which involves many signaling pathways and molecular mechanisms. Interestingly, recent studies indicate that the FoxO family is involved in a number of signaling pathways regulating cell differentiation. The actions occur at different stages in the differentiation process and by differing mechanisms. This review will focus on FoxO as a novel transcription factor in neural differentiation.

Querkopf is a key marker of self-renewal and multipotency of adult neural stem cells

Adult neural stem cells (NSCs) reside in the subventricular zone (SVZ) and produce neurons throughout life. Although their regenerative potential has kindled much interest, few factors regulating NSCs in vivo are known. Among these is the histone acetyltransferase querkopf (QKF, also known as MYST4, MORF, KAT6B), which is strongly expressed in a small subset of cells in the neurogenic subventricular zone. However, the relationship between Qkf gene expression and the hierarchical levels within the neurogenic lineage is currently unknown. We show here that the 10% of SVZ cells with the highest Qkf expression possess the defining NSC characteristics of multipotency and self-renewal and express markers previously shown to enrich for NSCs. A fraction of cells expressing Qkf at medium to high levels is enriched for multipotent progenitor cells with limited self-renewal, followed by a population containing migrating neuroblasts. Cells low in Qkf promoter activity are predominantly ependymal cells. In addition, we show that mice deficient for Bmi1, a central regulator of NSC self-renewal, show an age-dependent decrease in the strongest Qkf-expressing cell population in the SVZ. Our results show a strong relationship between Qkf promoter activity and stem cell characteristics, and a progressive decrease in Qkf gene activity as lineage commitment and differentiation proceed in vivo.

Clinical translation of stem cell therapy in traumatic brain injury: the potential of encapsulated mesenchymal cell biodelivery of glucagon-like peptide-1

Traumatic brain injury remains a major cause of death and disability; it is estimated that annually 10 million people are affected. Preclinical studies have shown the potential therapeutic value of stem cell therapies. Neuroprotective as well as regenerative properties of stem cells have been suggested to be the mechanism of action in preclinical studies. However, up to now stem cell therapy has not been studied extensively in clinical trials. This article summarizes the current experimental evidence and points out hurdles for clinical application. Focusing on a cell therapy in the acute stage of head injury, the potential of encapsulated cell biodelivery as a novel cell-therapeutic approach will also be discussed.

Toll-like receptor 3 regulates neural stem cell proliferation by modulating the Sonic Hedgehog pathway

Toll-like receptor 3 (TLR3) signaling has been implicated in neural stem/precursor cell (NPC) proliferation. However, the molecular mechanisms involved, and their relationship to classical TLR-mediated innate immune pathways, remain unknown. Here, we report investigation of the mechanics of TLR3 signaling in neurospheres comprised of epidermal growth factor (EGF)-responsive NPC isolated from murine embryonic cerebral cortex of C57BL/6 (WT) or TLR3 deficient (TLR3(-/-)) mice. Our data indicate that the TLR3 ligand polyinosinic-polycytidylic acid (PIC) negatively regulates NPC proliferation by inhibiting Sonic Hedgehog (Shh) signaling, that PIC induces apoptosis in association with inhibition of Ras-ERK signaling and elevated expression of Fas, and that these effects are TLR3-dependent, suggesting convergent signaling between the Shh and TLR3 pathways.

Dishevelled 2 signaling promotes self-renewal and tumorigenicity in human gliomas

Glioblastoma multiforme is the most common glioma variant in adults and is highly malignant. Tumors are thought to harbor a subpopulation of stem-like cancer cells, with the bulk resembling neural progenitor-like cells that are unable to fully differentiate. Although multiple pathways are known to be involved in glioma tumorigenesis, the role of Wnt signaling has been poorly described. Here, we show that Dishevelled 2 (Dvl2), a key component of the Wnt signaling pathway, is overexpressed in human gliomas. RNA interference-mediated depletion of Dvl2 blocked proliferation and promoted the differentiation of cultured human glioma cell lines and primary, patient-derived glioma cells. In addition, Dvl2 depletion inhibited tumor formation after intracranial injection of glioblastoma cells in immunodeficient mice. Inhibition of canonical Wnt/β-catenin signaling also blocked proliferation, but unlike Dvl2 depletion, did not induce differentiation. Finally, Wnt5a, a noncanonical Wnt ligand, was also required for glioma cell proliferation. The data therefore suggest that both canonical and noncanonical Wnt signaling pathways downstream of Dvl2 cooperate to maintain the proliferative capacity of human glioblastomas.

Differences between the neurogenic and proliferative abilities of Müller glia with stem cell characteristics and the ciliary epithelium from the adult human eye

Much controversy has arisen on the nature and sources of stem cells in the adult human retina. Whilst ciliary epithelium has been thought to constitute a source of neural stem cells, a population of Müller glia in the neural retina has also been shown to exhibit neurogenic characteristics. This study aimed to compare the neurogenic and proliferative abilities between these two major cell populations. It also examined whether differences exist between the pigmented and non-pigmented ciliary epithelium (CE) from the adult human eye. On this basis, Müller glia with stem cell characteristics and pigmented and non-pigmented CE were isolated from human neural retina and ciliary epithelium respectively. Expression of glial, epithelial and neural progenitor markers was examined in these cells following culture under adherent and non-adherent conditions and treatments to induce neural differentiation. Unlike pigmented CE which did not proliferate, non-pigmented CE cells exhibited limited proliferation in vitro, unless epidermal growth factor (EGF) was present in the culture medium to prolong their survival. In contrast, Müller glial stem cells (MSC) cultured as adherent monolayers reached confluence within a few weeks and continued to proliferative indefinitely in the absence of EGF. Both MSC and non-pigmented CE expressed markers of neural progenitors, including SOX2, PAX6, CHX10 and NOTCH. Nestin, a neural stem cell marker, was only expressed by MSC. Non-pigmented CE displayed epithelial morphology, limited photoreceptor gene expression and stained strongly for pigmented epithelial markers upon culture with neural differentiation factors. In contrast, MSC adopted neural morphology and expressed markers of retinal ganglion cells and photoreceptors when cultured under similar conditions. This study provides the first demonstration that pigmented CE possess different proliferative abilities from non-pigmented CE. It also showed that although non-pigmented CE express genes of retinal progenitors, they do not differentiate into neurons in vitro, as that seen with Müller glia that proliferate indefinitely in vitro and that acquire markers of retinal neurons in culture under neural differentiation protocols. From these observations it is possible to suggest that Müller glia that express markers of neural progenitors and become spontaneously immortalized in vitro constitute a potential source of retinal neurons for transplantation studies and fulfil the characteristics of true stem cells due to their proliferative and neurogenic ability.

Reduced oxygen stress promotes propagation of murine postnatal enteric neural progenitors in vitro

BACKGROUND

Neural stem and progenitor cells of the Enteric Nervous System (ENS) are regarded as a novel cell source for applications in regenerative medicine. However, improvements to the current ENS cell culture protocols will be necessary to generate clinically useful cell numbers under defined culture conditions. Beneficial effects of physiologically low oxygen concentrations and/or the addition of anti-oxidants on propagation of various types of stem cells have previously been demonstrated. In this study, we tested the effects of such culture conditions on ENS stem and progenitor cell behavior.

METHODS

Enteric neural progenitor cells were isolated from postnatal day 3 mouse intestine and propagated either as monolayers or neurosphere-like bodies. The influence of hypoxic culture conditions and/or anti-oxidants on enteric cell propagation were studied systematically using proliferation, differentiation and apoptosis assays, whereas effects on gene expression were determined by qRT-PCR, western blot, and immunocytochemistry.

KEY RESULTS

Both hypoxic culture conditions and anti-oxidants supported a significantly improved enteric cell propagation and the generation of differentiated neural cell types. Enteric neural progenitors were shown to be specifically vulnerable to persistent oxidative stress.

CONCLUSIONS & INFERENCES

Our findings are consistent with previous reports of improved maintenance of brain stem cells cultured under reduced oxygen stress conditions and may therefore be applied to future cell culture protocols in ENS stem cell research.

Nongenomic glucocorticoid receptor action regulates gap junction intercellular communication and neural progenitor cell proliferation

Glucocorticoids (GCs) are used to treat pregnant women at risk for preterm delivery; however, prenatal exposure to GCs may trigger adverse neurological side effects due to reduced neural progenitor cell (NPC) proliferation. Whereas many established cell-cycle regulators impact NPC proliferation, other signaling molecules, such as the gap junction protein connexin-43 (Cx43), also influence proliferation. Gap junction intercellular communication (GJIC) is influenced by GCs in some cells, but such hormone effects have not been examined in coupled stem cells. We found that both continuous and transient exposure of embryonic day 14.5 mouse neurosphere cultures to dexamethasone (DEX) limits proliferation of coupled NPCs, which is manifested by both a reduction in S-phase progression and enhanced cell-cycle exit. A short (i.e., 1-h) DEX treatment also reduced GJIC as measured by live-cell fluorescence recovery after photobleaching, and altered the synchrony of spontaneous calcium transients in coupled NPCs. GC effects on GJIC in NPCs are transcription-independent and mediated through plasma membrane glucocorticoid receptors (GRs). This nongenomic pathway operates through lipid raft-associated GRs via a site-specific, MAPK-dependent phosphorylation of Cx43, which is linked to GR via caveolin-1 (Cav-1) and c-src. Cav-1 is essential for this nongenomic action of GR, as DEX effects on GJIC, Cx43 phosphorylation, and MAPK activation are not observed in Cav-1 knockout NPCs. As transient pharmacologic inhibition of GJIC triggers reduced S-phase progression but not enhanced cell-cycle exit, the nongenomic GR signaling pathway may operate via distinct downstream effectors to alter the proliferative capacity of NPCs.

A protocol for isolation and enriched monolayer cultivation of neural precursor cells from mouse dentate gyrus

In vitro assays are valuable tools to study the characteristics of adult neural precursor cells under controlled conditions with a defined set of parameters. We here present a detailed protocol based on our previous original publication (Babu et al., 2007) to isolate neural precursor cells from the hippocampus of adult mice and maintain and propagate them as adherent monolayer cultures. The strategy is based on the use of Percoll density gradient centrifugation to enrich precursor cells from the micro-dissected dentate gyrus. Based on the expression of Nestin and Sox2, a culture-purity of more than 98% can be achieved. The cultures are expanded under serum-free conditions in Neurobasal A medium with addition of the mitogens Epidermal growth factor and Fibroblast growth factor 2 as well as the supplements Glutamax-1 and B27. Under differentiation conditions, the precursor cells reliably generate approximately 30% neurons with appropriate morphological, molecular, and electrophysiological characteristics that might reflect granule cell properties as their in vivo counterpart. We also highlight potential modifications to the protocol.

Glial commitment of mesencephalic neural precursor cells expanded as neurospheres precludes their engagement in niche-dependent dopaminergic neurogenesis

Neural precursor cells (NPCs) with high proliferative potential are commonly expanded in vitro as neurospheres. As a population, neurosphere cells show long-term self-renewal capacity and multipotentiality in vitro. These features have led to the assumption that neurosphere cells represent an expansion of the endogenous NPCs residing within the embryonic and adult brain. If this is the case, in principle, bona-fide expansion of endogenous NPCs should not significantly affect their capacity to respond to their original niche of differentiation. To address this issue, we generated primary neurospheres from the dopaminergic niche of the ventral mesencephalon and then transplanted these cells to their original niche within mesencephalic explant cultures. Primary neurosphere cells showed poor capacity to generate dopaminergic neurons in the mesencephalic niche of dopaminergic neurogenesis. Instead, most primary neurosphere cells showed glial commitment as they differentiated into astrocytes in an exclusively neurogenic niche. Subculture of primary cells demonstrated that the neurosphere assay does not amplify niche-responsive dopaminergic progenitors. Further, neurospheres cells were largely unable to acquire the endogenous positional identity within the Nkx6.1(+), Nkx2.2(+), and Pax7(+) domains of mesencephalic explants. Finally, we demonstrate that our observations are not specific for embryonic mesencephalic cells, as NPCs in the adult subventricular zone also showed an intrinsic fate switch from neuronal to glial potential upon neurosphere amplification. Our data suggest that neurosphere formation does not expand the endogenous neurogenic NPCs but rather promotes amplification of gliogenic precursors that do not respond to niche-derived signals of cellular specification and differentiation.

Over-expression of Oct4 in human esophageal squamous cell carcinoma

The Octamer 4 gene (Oct4) is a master pluripotency controller that has been detected in several types of tumors. Here, we examine the expression of Oct4 in human esophageal squamous cell carcinoma (ESCC). We found that punctate Oct4 protein was expressed in most (93.7%) ESCC samples but it was not observed in esophageal mucosa. Some ESCC cells had the capacity to form tumorospheres; those with an Oct4(+)-rich cell phenotype had increased proliferation and Oct4 mRNA levels compared to those of differentiated cells in culture or xenograft tumors. The over-expression of Oct4 in ESCCs suggests that it is a potential target for ESCC therapy. Oct4 could be a useful tumor marker in an immunohistochemical panel designed to differentiate between ESCC and esophageal mucosa. Expression of Oct4 in tumorospheres might indicate the presence of a population of ECSCs and its expression in xenograft tumors suggests that Oct4 is also associated with tumor metastasis.

Computer-aided 2D and 3D quantification of human stem cell fate from in vitro samples using Volocity high performance image analysis software

Accurate automated cell fate analysis of immunostained human stem cells from 2- and 3-dimensional (2D-3D) images would improve efficiency in the field of stem cell research. Development of an accurate and precise tool that reduces variability and the time needed for human stem cell fate analysis will improve productivity and interpretability of the data across research groups. In this study, we have created protocols for high performance image analysis software Volocity® to classify and quantify cytoplasmic and nuclear cell fate markers from 2D-3D images of human neural stem cells after in vitro differentiation. To enhance 3D image capture efficiency, we optimized the image acquisition settings of an Olympus FV10i® confocal laser scanning microscope to match our quantification protocols and improve cell fate classification. The methods developed in this study will allow for a more time efficient and accurate software based, operator validated, stem cell fate classification and quantification from 2D and 3D images, and yield the highest ≥94.4% correspondence with human recognized objects.

Flexibility of neural stem cells

Embryonic cortical neural stem cells are self-renewing progenitors that can differentiate into neurons and glia. We generated neurospheres from the developing cerebral cortex using a mouse genetic model that allows for lineage selection and found that the self-renewing neural stem cells are restricted to Sox2 expressing cells. Under normal conditions, embryonic cortical neurospheres are heterogeneous with regard to Sox2 expression and contain astrocytes, neural stem cells, and neural progenitor cells sufficiently plastic to give rise to neural crest cells when transplanted into the hindbrain of E1.5 chick and E8 mouse embryos. However, when neurospheres are maintained under lineage selection, such that all cells express Sox2, neural stem cells maintain their Pax6⁺ cortical radial glia identity and exhibit a more restricted fate in vitro and after transplantation. These data demonstrate that Sox2 preserves the cortical identity and regulates the plasticity of self-renewing Pax6⁺ radial glia cells.

Differentiation of neuronal cells from NIH/3T3 fibroblasts under defined conditions

We attempted to test whether the differentiated NIH/3T3 fibroblasts could be differentiated into neuronal cells without any epigenetic modification. First, a neurosphere assay was carried out, and we successfully generated neurosphere-like cells by floating cultures of NIH/3T3 fibroblasts in neural stem cell medium. These spheres have the ability to form sub-spheres after three passages, and express the neural progenitor markers Nestin, Sox2, Pax6, and Musashi-1. Second, after shifting to a differentiating medium and culturing for an additional 8 days, cells in these spheres expressed the neuronal markers β-tubulin and neurofilament 200 and the astrocytic marker glial fibrillary acidic protein (GFAP). Finally, after treating the spheres with all-trans retinoic acid and taurine, the expression of β-tubulin was increased and the staining of photoreceptor markers rhodopsin and recoverin was observed. The present study shows that NIH/3T3 fibroblasts can generate neurosphere-like, neuron-like, and even photoreceptor-like cells under defined conditions, suggesting that the differentiated non-neuronal cells NIH/3T3 fibroblasts, but not pluripotent cells such as embryonic stem cells or induced pluripotent stem cells, may have the potential to be transdifferentiated into neuronal cells without adding any epigenetic modifier. This transdifferentiation may be due to the possible neural progenitor potential of NIH/3T3 fibroblasts that remains dormant under normal conditions.

Moderate fetal alcohol exposure impairs neurogenic capacity of murine neural stem cells isolated from the adult subventricular zone

Gestational alcohol exposure leads to a spectrum of neurological symptoms which range from severe mental retardation caused by high dose exposure, to subtle cognitive and neuropsychiatric symptoms caused by low-to-moderate doses. We and other investigators have demonstrated that exposure to moderate levels of alcohol throughout gestation leads to impaired neurogenesis in the adult hippocampus, although the mechanisms by which this occurs are not known. To begin to distinguish cell-intrinsic from microenvironmental contributions to impaired adult neurogenesis, we isolated neural stem progenitor cells (NSPCs) from the adult SVZ of mice exposed to moderate levels of alcohol throughout gestation. We found that NSPCs isolated from fetal alcohol exposed (FAE) mice displayed reduced neurosphere formation in culture, as assessed by a serial passage neurosphere assay, and reduced neuronal differentiation upon growth factor withdrawal. These studies suggest that gestational alcohol exposure leads to long-lasting NSPC-intrinsic dysregulation, which may underlie in vivo neurogenic deficits.

Investigating monogenic and complex diseases with pluripotent stem cells

Human genetic studies have revealed the molecular basis of countless monogenic diseases but have been less successful in associating phenotype to genotype in complex multigenic conditions. Pluripotent stem cells (PSCs), which can differentiate into any cell type, offer promise for defining the functional effects of genetic variation. Here, we recount the advantages and practical limitations of coupling PSCs to genome-wide analyses to probe complex genetics and discuss the ability to investigate epigenetic contributions to disease states. We also describe new ways of using mice and mouse embryonic stem cells (ESCs) in tandem with human stem cells to further define genotype-phenotype relationships.

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

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

Modulation of the generation of dopaminergic neurons from human neural stem cells by Bcl-X(L): mechanisms of action

Understanding the developmental mechanisms governing dopaminergic neuron generation and maintenance is crucial for the development of neuronal replacement therapeutic procedures, like in Parkinson's disease (PD), but also for research aimed at drug screening and pharmacology. In the present chapter, we review the present situation using stem cells of different origins (pluripotent and multipotent) and summarize current manipulations of stem cells for the enhancement of dopaminergic neuron generation, focusing on the actions of Bcl-X(L). Bcl-X(L) not only enhances dopaminergic neuron survival but also augments the expression of key developmental and maintenance genes, and, through the lengthening of the cell cycle early during differentiation, regulates cell fate decisions, producing a net enhancement of neurogenesis. The relevance of these findings is discussed in the context of basic neurogenesis and also for the development of efficient cell therapy in PD.

Human neurospheres: From stained sections to three-dimensional assembly

Human neurospheres are free-floating spherical clusters generated from a single neural stem cell and comprising cells at different stages of maturation in the neuronal and glial lineages. Although recent findings have disproved the original idea of clonally derived neurospheres according to the paradigm of one stem cell — one neurosphere, they still represent a valid model for growing neural stem cell cultures in vitro. While the immunocytochemical approach to the identification of stem cells, progenitor cells, and mature cells has been extensively used, scant data are available about the ultrastructural arrangement of different cell types within the neurosphere. This paper provides, by means of scanning electron microscopy, some new insights into the three-dimensional assembly of human neurospheres, trying to correlate some parameters such as cell density, shape and growing strategies with the immunolocalization of some antigens such as nestin, GFAP, α-internexin and βIII-tubulin. The major findings from this study are: a) regardless of the stage of in vitro maturation, the growth of the spheres is the result of mitotic divisions producing the aspect of an irregular budding mechanism in the outermost layer look like; b) analysis of the volumetric composition of the inner core has revealed the presence of two alternative shape pattern (pyramidal vs rounded cells) possibly related to both the ongoing maturation stages and GFAP and internexin expression.

A comparative study of the structural organization of spheres derived from the adult human subventricular zone and glioblastoma biopsies

Sphere forming assays have been useful to enrich for stem like cells in a range of tumors. The robustness of this system contrasts the difficulties in defining a stem cell population based on cell surface markers. We have undertaken a study to describe the cellular and organizational composition of tumorspheres, directly comparing these to neurospheres derived from the adult human subventricular zone (SVZ). Primary cell cultures from brain tumors were found to contain variable fractions of cells positive for tumor stem cell markers (CD133 (2-93%)/SSEA1 (3-15%)/CXCR4 (1-72%)). All cultures produced tumors upon xenografting. Tumorspheres contained a heterogeneous population of cells, but were structurally organized with stem cell markers present at the core of spheres, with markers of more mature glial progenitors and astrocytes at more peripheral location. Ultrastructural studies showed that tumorspheres contained a higher fraction of electron dense cells in the core than the periphery (36% and 19%, respectively). Neurospheres also contained a heterogeneous cell population, but did not have an organization similar to tumorspheres. Although tumorspheres clearly display irregular and neoplastic cells, they establish an organized structure with an outward gradient of differentiation. We suggest that this organization is central in maintaining the tumor stem cell pool.

p73 regulates maintenance of neural stem cell

p73, a member of the p53 family, is a transcription factor that plays a key role in many biological processes. In the present study, we show that TAp73 is expressed in neural stem cells (NSC) and its expression increases following their differentiation. NSC from p73 null mice have a reduced proliferative potential, together with reduced expression of members of the Sox-2 and Notch gene families known to be important for NSC proliferation. In parallel with this in vitro data, the width of the neurogenic areas was reduced in the brains of embryonic and adult p73−/− mice. These data suggest that p73, and in particular TAp73, is important for maintenance of the NSC pool.

New-generation taxoid SB-T-1214 inhibits stem cell-related gene expression in 3D cancer spheroids induced by purified colon tumor-initiating cells

Background

Growing evidence suggests that the majority of tumors are organized hierarchically, comprising a population of tumor-initiating, or cancer stem cells (CSCs) responsible for tumor development, maintenance and resistance to drugs. Previously we have shown that the CD133^high/CD44^high fraction of colon cancer cells is different from their bulk counterparts at the functional, morphological and genomic levels. In contrast to the majority of colon cancer cells expressing moderate levels of CD133, CD44 and CD166, cells with a high combined expression of CD133 and CD44 possessed several characteristic stem cell features, including profound self-renewal capacity in vivo and in vitro, and the ability to give rise to different cell phenotypes. The present study was undertaken for two aims: a) to determine stem cell-related genomic characteristics of floating 3D multicellular spheroids induced by CD133^high/CD44^high colon cancer cells; and b) to evaluate CSC-specific alterations induced by new-generation taxoid SB-T-1214.

Results

Selected CSC phenotype was isolated from three independent invasive colon cancer cell lines, HCT116, HT29 and DLD-1. A stem cell-specific PCR array assay (SABiosciences) revealed that colonospheres induced by purified CD133^high/CD44^high expressing cells display profound up-regulation of stem cell-related genes in comparison with their bulk counterparts. The FACS analysis has shown that the 3D colonospheres contained some minority cell populations with high levels of expression of Oct4, Sox2, Nanog and c-Myc, which are essential for stem cell pluripotency and self-renewal. Single administration of the SB-T-1214 at concentration 100 nM-1 μM for 48 hr not only induced growth inhibition and apoptotic cell death in these three types of colon cancer spheroids in 3D culture, but also mediated massive inhibition of the stem cell-related genes and significant down-regulation of the pluripotency gene expression. PCR array and FACS data were confirmed with western blotting. Importantly, viable cells that survived this treatment regimen were no longer able to induce secondary floating spheroids and exhibited significant morphological abnormalities.

Conclusions

We report here that a new-generation taxoid SB-T-1214 possesses significant activity against colon cancer spheroids induced by and enriched with drug resistant tumorigenic CD133^high/CD44^high cells and efficiently inhibited expression of the majority of stem cell-related genes. Our data indicates that the previously observed long-term efficacy of SB-T-1214 against drug resistant colon tumors in vivo may be explained by the down-regulation of multiple stem cell-related genes in the tumorigenic cell population, in addition to its known efficacy as a mitotic poison against proliferating cancer cells.

Head and neck cancer stem cells: the side population

OBJECTIVES/HYPOTHESIS

The cancer stem cell (CSC) theory concludes that a subpopulation of cancer cells, the cancer stem cells, can self-renew and are responsible for tumor growth. Previous studies have identified cells able to efflux Hoechst 33342 dye as the side population (SP). SP cells and CSCs share many characteristics, suggesting the SP isolated from malignant tumors contains CSCs.

STUDY DESIGN

Experimental Study.

METHODS

The SP was isolated from a head and neck cancer cell line and analyzed for CSC-like characteristics.

RESULTS

The SP demonstrated the ability to reproduce both SP and non-side population (NSP) cells from as few as one cell. The SP had lower expression of active β-catenin and more resistance to 5-fluorouracil; the SP also demonstrated greater expression of Bmi-1 (4.3-fold) and ABCG2 (1.4-fold). SP cells were able to produce tumors in an animal model, whereas NSP were not. SPs were identified in two primary human tumors.

CONCLUSIONS

This work adds to the evidence that the SP in head and neck cancer represents cells with CSC properties and provides a method by which CSCs can be isolated and studied.

The in vitro spheroid melanoma cell culture assay: cues on tumor initiation?

Cancer stem cells (CSCs) represent malignant subpopulations that initiate and maintain tumorigenic growth in hierarchically organized tumors via their considerable capacity for self-renewal and differentiation. CSCs have been identified in several human malignancies, including human malignant melanoma. Perego and colleagues' report in this issue indicates that CSCs capable of melanoma initiation in serial human-to-mouse xenotransplantation assays may be contained both among spheroid melanoma cell cultures (melanospheres) and among adherent melanoma cultures upon in vitro expansion. These results challenge the utility of the melanosphere assay as a surrogate tool for CSC identification in human melanomas and underline the importance of molecularly defined malignant melanoma initiating cells for CSC-focused diagnostic and therapeutic investigations.

Challenges of stem cell therapy for spinal cord injury: human embryonic stem cells, endogenous neural stem cells, or induced pluripotent stem cells?

Spinal cord injury (SCI) causes myelopathy, damage to white matter, and myelinated fiber tracts that carry sensation and motor signals to and from the brain. The gray matter damage causes segmental losses of interneurons and motoneurons and restricts therapeutic options. Recent advances in stem cell biology, neural injury, and repair, and the progress toward development of neuroprotective and regenerative interventions are the basis for increased optimism. This review summarizes the pathophysiological mechanisms following SCI and compares human embryonic, adult neural, and the induced pluripotent stem cell-based therapeutic strategies for SCI.

In vitro and in vivo enhanced generation of human A9 dopamine neurons from neural stem cells by Bcl-XL

Human neural stem cells derived from the ventral mesencephalon (VM) are powerful research tools and candidates for cell therapies in Parkinson disease. Previous studies with VM dopaminergic neuron (DAn) precursors indicated poor growth potential and unstable phenotypical properties. Using the model cell line hVM1 (human ventral mesencephalic neural stem cell line 1; a new human fetal VM stem cell line), we have found that Bcl-X(L) enhances the generation of DAn from VM human neural stem cells. Mechanistically, Bcl-X(L) not only exerts the expected antiapoptotic effect but also induces proneural (NGN2 and NEUROD1) and dopamine-related transcription factors, resulting in a high yield of DAn with the correct phenotype of substantia nigra pars compacta (SNpc). The expression of key genes directly involved in VM/SNpc dopaminergic patterning, differentiation, and maturation (EN1, LMX1B, PITX3, NURR1, VMAT2, GIRK2, and dopamine transporter) is thus enhanced by Bcl-X(L). These effects on neurogenesis occur in parallel to a decrease in glia generation. These in vitro Bcl-X(L) effects are paralleled in vivo, after transplantation in hemiparkinsonian rats, where hVM1-Bcl-X(L) cells survive, integrate, and differentiate into DAn, alleviating behavioral motor asymmetry. Bcl-X(L) then allows for human fetal VM stem cells to stably generate mature SNpc DAn both in vitro and in vivo and is thus proposed as a helpful factor for the development of cell therapies for neurodegenerative conditions, Parkinson disease in particular.

The fibroblast growth factor receptor substrate 3 adapter is a developmentally regulated microtubule-associated protein expressed in migrating and differentiated neurons

Fibroblast growth factor (FGF) mediated signaling is essential to many aspects of neural development. Activated FGF receptors signal primarily through the FGF receptor substrate (Frs) adapters, which include Frs2/Frs2alpha and Frs3/Frs2beta. While some studies suggest that Frs3 can compensate for the loss of Frs2 in transfected cells, the lack of an effective Frs3 specific antibody has prevented efforts to determine the role(s) of the endogenous protein. To this end, we have generated a Frs3 specific antibody and have characterized the pattern of Frs3 expression in the developing nervous system, its subcellular localization as well as its biochemical properties. We demonstrate that Frs3 is expressed at low levels in the ventricular zone of developing cortex, between E12 and E15, and it co-localizes with nestin and acetylated alpha-tubulin in radial processes in the ventricular/subventricular zones as well as with betaIII tubulin in differentiated cortical neurons. Subcellular fractionation studies demonstrate that endogenous Frs3 is both soluble and plasma membrane associated while Frs3 expressed in 293T cells associates exclusively with lipid rafts. Lastly, we demonstrate that neuronal Frs3 binds microtubules comparable to the microtubule-associated protein, MAP2, while Frs2 does not. Collectively, these data suggest that neuronal Frs3 functions as a novel microtubule binding protein and they provide the first biochemical evidence that neuronal Frs3 is functionally distinct from Frs2/Frs2alpha.