Defining the actual sensitivity and specificity of the neurosphere assay in stem cell biology

Single-cell mRNA profiling identifies progenitor subclasses in neurospheres

Neurospheres are widely used to propagate and investigate neural stem cells (NSCs) and neural progenitors (NPs). However, the exact cell types present within neurospheres are still unknown. To identify cell types, we used single-cell mRNA profiling of 48 genes in 187 neurosphere cells. Using a clustering algorithm, we identified 3 discrete cell populations within neurospheres. One cell population [cluster unsorted (US) 1] expresses high Bmi1 and Hes5 and low Myc and Klf12. Cluster US2 shows intermediate expression of most of the genes analyzed. Cluster US3 expresses low Bmi1 and Hes5 and high Myc and Klf12. The mRNA profiles of these 3 cell populations correlate with a developmental timeline of early, intermediate, and late NPs, as seen in vivo from the mouse brain. We enriched the cell population for neurosphere-forming cells (NFCs) using morphological criteria of forward scatter (FSC) and side scatter (SSC). FSC/SSC(high) cells generated 2.29-fold more neurospheres than FSC/SSC(low) cells at clonal density. FSC/SSC(high) cells were enriched for NSCs and Lewis-X(+ve) cells, possessed higher phosphacan levels, and were of a larger cell size. Clustering of both FSC/SSC(high) and FSC/SSC(low) cells identified an NFC cluster. Significantly, the mRNA profile of the NFC cluster drew close resemblance to that of early NPs. Taken together, data suggest that the neurosphere culture system can be used to model central nervous system development, and that early NPs are the cell population that gives rise to neurospheres. In future work, it may be possible to further dissect the NFCs and reveal the molecular signature for NSCs.

Taurine induces proliferation of neural stem cells and synapse development in the developing mouse brain

Taurine is a sulfur-containing amino acid present in high concentrations in mammalian tissues. It has been implicated in several processes involving brain development and neurotransmission. However, the role of taurine in hippocampal neurogenesis during brain development is still unknown. Here we show that taurine regulates neural progenitor cell (NPC) proliferation in the dentate gyrus of the developing brain as well as in cultured early postnatal (P5) hippocampal progenitor cells and hippocampal slices derived from P5 mice brains. Taurine increased cell proliferation without having a significant effect on neural differentiation both in cultured P5 NPCs as well as cultured hippocampal slices and in vivo. Expression level analysis of synaptic proteins revealed that taurine increases the expression of Synapsin 1 and PSD 95. We also found that taurine stimulates the phosphorylation of ERK1/2 indicating a possible role of the ERK pathway in mediating the changes that we observed, especially in proliferation. Taken together, our results demonstrate a role for taurine in neural stem/progenitor cell proliferation in developing brain and suggest the involvement of the ERK1/2 pathways in mediating these actions. Our study also shows that taurine influences the levels of proteins associated with synapse development. This is the first evidence showing the effect of taurine on early postnatal neuronal development using a combination of in vitro, ex-vivo and in vivo systems.

G-protein-coupled receptors in adult neurogenesis

The importance of adult neurogenesis has only recently been accepted, resulting in a completely new field of investigation within stem cell biology. The regulation and functional significance of adult neurogenesis is currently an area of highly active research. G-protein-coupled receptors (GPCRs) have emerged as potential modulators of adult neurogenesis. GPCRs represent a class of proteins with significant clinical importance, because approximately 30% of all modern therapeutic treatments target these receptors. GPCRs bind to a large class of neurotransmitters and neuromodulators such as norepinephrine, dopamine, and serotonin. Besides their typical role in cellular communication, GPCRs are expressed on adult neural stem cells and their progenitors that relay specific signals to regulate the neurogenic process. This review summarizes the field of adult neurogenesis and its methods and specifies the roles of various GPCRs and their signal transduction pathways that are involved in the regulation of adult neural stem cells and their progenitors. Current evidence supporting adult neurogenesis as a model for self-repair in neuropathologic conditions, adult neural stem cell therapeutic strategies, and potential avenues for GPCR-based therapeutics are also discussed.

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.

Assembling neurospheres: dynamics of neural progenitor/stem cell aggregation probed using an optical trap

Optical trapping (tweezing) has been used in conjunction with fluid flow technology to dissect the mechanics and spatio-temporal dynamics of how neural progenitor/stem cells (NSCs) adhere and aggregate. Hitherto unavailable information has been obtained on the most probable minimum time (∼5 s) and most probable minimum distance of approach (4–6 µm) required for irreversible adhesion of proximate cells to occur. Our experiments also allow us to study and quantify the spatial characteristics of filopodial- and membrane-mediated adhesion, and to probe the functional dynamics of NSCs to quantify a lower limit of the adhesive force by which NSCs aggregate (∼18 pN). Our findings, which we also validate by computational modeling, have important implications for the neurosphere assay: once aggregated, neurospheres cannot disassemble merely by being subjected to shaking or by thermal effects. Our findings provide quantitative affirmation to the notion that the neurosphere assay may not be a valid measure of clonality and “stemness”. Post-adhesion dynamics were also studied and oscillatory motion in filopodia-mediated adhesion was observed. Furthermore, we have also explored the effect of the removal of calcium ions: both filopodia-mediated as well as membrane-membrane adhesion were inhibited. On the other hand, F-actin disrupted the dynamics of such adhesion events such that filopodia-mediated adhesion was inhibited but not membrane-membrane adhesion.

A detailed mammosphere assay protocol for the quantification of breast stem cell activity

Since the discovery that neural tissue contains a population of stem cells that form neurospheres in vitro, sphere-forming assays have been adapted for use with a number of different tissue types for the quantification of stem cell activity and self-renewal. One tissue type widely used for stem cell investigations is mammary tissue, and the mammosphere assay has been used in both normal tissue and cancer. Although it is a relatively simple assay to learn, it can be difficult to master. There are methodological and analytical aspects to the assay which require careful consideration when interpreting the results. We describe here a detailed mammosphere assay protocol for the assessment of stem cell activity and self-renewal, and discuss how data generated by the assay can be analysed and interpreted.

Neural stem cells: brain building blocks and beyond

Neural stem cells are the origins of neurons and glia and generate all the differentiated neural cells of the mammalian central nervous system via the formation of intermediate precursors. Although less frequent, neural stem cells persevere in the postnatal brain where they generate neurons and glia. Adult neurogenesis occurs throughout life in a few limited brain regions. Regulation of neural stem cell number during central nervous system development and in adult life is associated with rigorous control. Failure in this regulation may lead to e.g. brain malformation, impaired learning and memory, or tumor development. Signaling pathways that are perturbed in glioma are the same that are important for neural stem cell self-renewal, differentiation, survival, and migration. The heterogeneity of human gliomas has impeded efficient treatment, but detailed molecular characterization together with novel stem cell-like glioma cell models that reflect the original tumor gives opportunities for research into new therapies. The observation that neural stem cells can be isolated and expanded in vitro has opened new avenues for medical research, with the hope that they could be used to compensate the loss of cells that features in several severe neurological diseases. Multipotent neural stem cells can be isolated from the embryonic and adult brain and maintained in culture in a defined medium. In addition, neural stem cells can be derived from embryonic stem cells and induced pluripotent stem cells by in vitro differentiation, thus adding to available models to study stem cells in health and disease.

Cellular characteristics of head and neck cancer stem cells in type IV collagen-coated adherent cultures

Although head and neck squamous carcinoma cancer stem cells (HNSC-CSCs) can be enriched in serum-free suspension cultures, it is difficult to stably expand HNSC-CSC lines in suspension due to spontaneous apoptosis and differentiation. Here, we investigated whether HNSC-CSCs can be expanded without loss of stem cell properties by adherent culture methods. Cell culture plates were coated with type IV collagen, laminin, or fibronectin. We examined cancer stem cell traits of adherent HNSC-CSCs grown on these plates using immunocytochemistry for stem cell marker expression and analyses of chemo-resistance and xenograft tumorigenicity. We also assessed the growth rate, apoptosis rate, and gene transduction efficiency of adherent and suspended HNSC-CSCs. HNSC-CSCs grew much faster on type IV collagen-coated plates than in suspension. Adherent HNSC-CSCs expressed putative stem cell markers (OCT4 and CD44) and were chemo-resistant to various cytotoxic drugs (cisplatin, fluorouracil, paclitaxel, and docetaxel). Adherent HNSC-CSCs at the limiting dilution (1000 cells) produced tumors in nude mice. Adherent HNSC-CSCs also showed less spontaneous apoptotic cell death and were more competent to lentiviral transduction than suspended HNSC-CSCs. In conclusion, compared to suspension cultures, adherence on type IV collagen-coated culture plates provides better experimental conditions for HNSC-CSC expansion, which should facilitate various refined cellular studies.

Loss of protein-tyrosine phosphatase α (PTPα) increases proliferation and delays maturation of oligodendrocyte progenitor cells

Tightly controlled termination of proliferation determines when oligodendrocyte progenitor cells (OPCs) can initiate differentiation and mature into myelin-forming cells. Protein-tyrosine phosphatase α (PTPα) promotes OPC differentiation, but its role in proliferation is unknown. Here we report that loss of PTPα enhanced in vitro proliferation and survival and decreased cell cycle exit and growth factor dependence of OPCs but not neural stem/progenitor cells. PTPα(-/-) mice have more oligodendrocyte lineage cells in embryonic forebrain and delayed OPC maturation. On the molecular level, PTPα-deficient mouse OPCs and rat CG4 cells have decreased Fyn and increased Ras, Cdc42, Rac1, and Rho activities, and reduced expression of the Cdk inhibitor p27Kip1. Moreover, Fyn was required to suppress Ras and Rho and for p27Kip1 accumulation, and Rho inhibition in PTPα-deficient cells restored expression of p27Kip1. We propose that PTPα-Fyn signaling negatively regulates OPC proliferation by down-regulating Ras and Rho, leading to p27Kip1 accumulation and cell cycle exit. Thus, PTPα acts in OPCs to limit self-renewal and facilitate differentiation.

Cancer vaccination drives Nanog-dependent evolution of tumor cells toward an immune-resistant and stem-like phenotype

Due to the exquisite specificity and potency of the immune system, vaccination is in theory the most precise and powerful approach for controlling cancer. However, current data from clinical trials indicate that vaccination rarely yields significant benefits for cancer patients in terms of tumor progression and long-term survival. The poor clinical outcomes of vaccination are primarily caused by mechanisms of immune tolerance, especially within the tumor microenvironment. Here, we report that vaccination drives the evolution of tumor cells toward an immune-resistant and stem-like phenotype that promotes tumor growth and nullifies the CTL response. The emergence of this phenotype required the transcription factor Nanog, which is induced as a consequence of immune selection. Nanog expression enhanced the stem-like features of tumor cells and protected them from killing by tumor-reactive CTLs. Delivery of siNanog into tumor-bearing mice rendered the tumor vulnerable to immune surveillance and strongly suppressed its growth. Together, our findings show tumor adaptation to vaccination through gain of an immune-resistant, stem-like phenotype and identify Nanog as a central molecular target in this process. Future vaccination technology should consider Nanog an important target to enhance the immunotherapeutic response.

High-throughput clonal analysis of neural stem cells in microarrayed artificial niches

To better understand the extrinsic signals that control neural stem cell (NSC) fate, here we applied a microwell array platform which allows high-throughput clonal analyses of NSCs, cultured either as neurospheres or as adherent clones, exposed to poly(ethylene glycol) (PEG) hydrogel substrates functionalized with selected signaling molecules. We analyzed by time-lapse microscopy and retrospective immunostaining the role of integrin and Notch ligands, two key NSC niche components, in altering the behavior of several hundred single stem cells isolated from a previously described Hes5::GFP reporter mouse. NSC self-renewal was increased by 1.5-fold upon exposure to covalently tethered Laminin-1 and fibronectin fragment 9-10 (FN(9-10)), where 60-65% of single cells proliferated extensively and remained Nestin positive. Tethering of the Notch ligand Jagged-1 induced activation of Notch signaling. While Jagged-1 alone increased cell survival and proliferation, no further increase in the clonogenic potential of Hes5::GFP cells was observed upon co-stimulation with Laminin-1 and Jagged-1. We believe that the bioengineering of such in vitro niche analogues is a powerful approach to elucidate single stem cell fate regulation in a well-controlled fashion.

Selective inhibitory effect of HPMA copolymer-cyclopamine conjugate on prostate cancer stem cells

Improved treatments for prostate cancer are in great need to overcome lethal recurrence and metastasis. Targeting the tumorigenic cancer stem cells (CSCs) with self-renewal and differentiation capacity appears to be a promising strategy. Blockade of the hedgehog (Hh) signaling pathway, an important pathway involved in stem cell self-renewal, by cyclopamine leads to long-term prostate cancer regression without recurrence, strongly suggesting the connection between Hh pathway and prostate CSCs. Here we designed an HPMA (N-(2-hydroxypropyl)methacrylamide)-based cyclopamine delivery system as a CSC-selective macromolecular therapeutics with improved drug solubility and decreased systemic toxicity. To this end, HPMA and N-methacryloylglycylphenylalanylleucylglycyl thiazolidine-2-thione were copolymerized using the RAFT (reversible addition-fragmentation chain transfer) process, followed by polymer-analogous attachment of cyclopamine. The selectivity of the conjugate toward CSCs was evaluated on RC-92a/hTERT cells, the human prostate cancer epithelial cells with human telomerase reverse transcriptase transduction. The use of RC-92a/hTERT cells as an in vitro CSC model was validated by stem cell marker expression and prostasphere culture. The bioactivity of cyclopamine was retained after conjugation to the polymer. Furthermore, HPMA polymer-conjugated cyclopamine showed anti-CSC efficacy on RC-92a/hTERT cells as evaluated by decreased stem cell marker expression and CSC viability.

Twisted tango: brain tumor neurovascular interactions

The brain is a complicated organ with complexity derived from cellular and microenvironmental interactions. Similarly, brain tumor cells actively modify and are regulated by their microenvironment. Brain tumors are highly heterogeneous and frequently show a cellular hierarchy with self-renewing tumorigenic brain tumor stem cells (BTSCs) at the apex. Although BTSCs are distinct from neural stem cells, they share characteristics, including bidirectional interplay with supportive vasculature critical for maintenance of undifferentiated states and survival. BTSCs stimulate angiogenesis through growth factor secretion and are enriched in perivascular niches. Microenvironmental conditions, including hypoxia, drive expression of stem cell genes and proangiogenic factors, further linking cellular hierarchy regulation and instructive stromal elements. BTSCs may also directly contribute to tumor vasculature through plasticity toward an endothelial lineage. Interrogating the codependence of BTSCs and the perivascular niche may directly inform clinical approaches for brain tumor therapy through targeting of highly angiogenic and tumorigenic cellular subsets.

Eyes wide open: a critical review of sphere-formation as an assay for stem cells

Sphere-forming assays have been widely used to retrospectively identify stem cells based on their reported capacity to evaluate self-renewal and differentiation at the single-cell level in vitro. The discovery of markers that allow the prospective isolation of stem cells and their progeny from their in vivo niche allows the functional properties of purified populations to be defined. We provide a historical perspective of the evolution of the neurosphere assay and highlight limitations in the use of sphere-forming assays in the context of neurospheres. We discuss theoretical and technical considerations of experimental design and interpretation that surround the use of this assay with any tissue.

Seeing is believing: are cancer stem cells the Loch Ness monster of tumor biology?

Tumors are complex systems with a diversity of cell phenotypes essential to tumor initiation and maintenance. With the heterogeneity present within the neoplastic compartment as its foundation, the cancer stem cell hypothesis posits that a fraction of tumor cells has the capacity to recapitulate the parental tumor upon transplantation. Over the last decade, the cancer stem cell hypothesis has gained support and shown to be relevant in many highly lethal solid tumors. However, the cancer stem cell hypothesis is not without its controversies and critics question the validity of this hypothesis based upon comparisons to normal somatic stem cells. Cancer stem cells may have direct therapeutic relevance due to resistance to current treatment paradigms, suggesting novel multimodal therapies targeting the cancer stem cells may improve patient outcomes. In this review, we will use the most common primary brain tumor, glioblastoma multiforme, as an example to illustrate why studying cancer stem cells holds great promise for more effective therapies to highly lethal tumors. In addition, we will discuss why the abilities of self-renewal and tumor propagation are the critical defining properties of cancer stem cells. Furthermore, we will examine recent progress in defining appropriate cell surface selection markers and mouse models which explore the potential cell(s) or origin for GBMs. What remains clear is that a population of cells is present in many tumors which are resistant to conventional therapies and must be considered in the design of the next generation of cancer treatments.

A molecular screening approach to identify and characterize inhibitors of glioblastoma stem cells

Glioblastoma (GBM) is among the most lethal of all cancers. GBM consist of a heterogeneous population of tumor cells among which a tumor-initiating and treatment-resistant subpopulation, here termed GBM stem cells, have been identified as primary therapeutic targets. Here, we describe a high-throughput small molecule screening approach that enables the identification and characterization of chemical compounds that are effective against GBM stem cells. The paradigm uses a tissue culture model to enrich for GBM stem cells derived from human GBM resections and combines a phenotype-based screen with gene target-specific screens for compound identification. We used 31,624 small molecules from 7 chemical libraries that we characterized and ranked based on their effect on a panel of GBM stem cell-enriched cultures and their effect on the expression of a module of genes whose expression negatively correlates with clinical outcome: MELK, ASPM, TOP2A, and FOXM1b. Of the 11 compounds meeting criteria for exerting differential effects across cell types used, 4 compounds showed selectivity by inhibiting multiple GBM stem cells-enriched cultures compared with nonenriched cultures: emetine, n-arachidonoyl dopamine, n-oleoyldopamine (OLDA), and n-palmitoyl dopamine. ChemBridge compounds #5560509 and #5256360 inhibited the expression of the 4 mitotic module genes. OLDA, emetine, and compounds #5560509 and #5256360 were chosen for more detailed study and inhibited GBM stem cells in self-renewal assays in vitro and in a xenograft model in vivo. These studies show that our screening strategy provides potential candidates and a blueprint for lead compound identification in larger scale screens or screens involving other cancer types.

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.

Role of stem cells in cardiovascular biology

This review article addresses the controversy as to whether the adult heart possesses an intrinsic growth reserve. If myocyte renewal takes place in healthy and diseased organs, the reconstitution of the damaged tissue lost upon pathological insults might be achieved by enhancing a natural occurring process. Evidence in support of the old and new view of cardiac biology is critically discussed in an attempt to understand whether the heart is a static or dynamic organ. According to the traditional concept, the heart exerts its function until death of the organism with the same or lesser number of cells that are present at birth. This paradigm was challenged by documentation of the cell cycle activation and nuclear and cellular division in a subset of myocytes. These observations raised the important question of the origin of replicating myocytes. Several theories have been proposed and are presented in this review article. Newly formed myocytes may derive from a pre-existing pool of cells that has maintained the ability to divide. Alternatively, myocytes may be generated by activation and commitment of resident cardiac stem cells or by migration of progenitor cells from distant organs. In all cases, parenchymal cell turnover throughout lifespan results in a heterogeneous population consisting of young, adult, and senescent myocytes. With time, accumulation of old myocytes has detrimental effects on cardiac performance and may cause the development of an aging myopathy.

Distinctive effects of arachidonic acid and docosahexaenoic acid on neural stem /progenitor cells

Arachidonic acid (ARA) and docosahexaenoic acid (DHA), which are the dominant polyunsaturated fatty acids in the brain, have crucial roles in brain development and function. Recent studies have shown that ARA and DHA promote postnatal neurogenesis. However, the direct effects of ARA on neural stem/progenitor cells (NSPCs) and the effects of ARA and DHA on NSPCs at the neurogenic and subsequent gliogenic stages are still unknown. Here, we analyzed the effects of ARA and DHA on neurogenesis, specifically maintenance and differentiation, using neurosphere assays. We confirmed that primary neurospheres are neurogenic NSPCs and that tertiary neurospheres are gliogenic NSPCs. Regarding the effects of ARA and DHA on neurogenic NSPCs, ARA and DHA increased the number of neurospheres, whereas neither ARA nor DHA had a detectable effect on NSPCs in the differentiation condition. In gliogenic NSPCs, DHA increased the number of neurospheres, whereas ARA had no such effect. In contrast, ARA increased the number of astrocytes, whereas DHA increased the number of neurons in the differentiation condition. These results suggest that ARA promotes the maintenance of neurogenic NSPCs and might induce the glial differentiation of gliogenic NSPCs and that DHA promotes the maintenance of both neurogenic and gliogenic NSPCs and might lead to the neuronal differentiation of gliogenic NSPCs.

Nestin is required for the proper self-renewal of neural stem cells

The intermediate filament protein, nestin, is a widely employed marker of multipotent neural stem cells (NSCs). Recent in vitro studies have implicated nestin in a number of cellular processes, but there is no data yet on its in vivo function. Here, we report the construction and functional characterization of Nestin knockout mice. We found that these mice show embryonic lethality, with neuroepithelium of the developing neural tube exhibiting significantly fewer NSCs and much higher levels of apoptosis. Consistent with this in vivo observation, NSC cultures derived from knockout embryos show dramatically reduced self-renewal ability that is associated with elevated apoptosis but no overt defects in cell proliferation or differentiation. Unexpectedly, nestin deficiency has no detectable effect on the integrity of the cytoskeleton. Furthermore, the knockout of Vimentin, which abolishes nestin's ability to polymerize into intermediate filaments in NSCs, does not lead to any apoptotic phenotype. These data demonstrate that nestin is important for the proper survival and self-renewal of NSCs, and that this function is surprisingly uncoupled from nestin's structural involvement in the cytoskeleton.

Equivalent neurogenic potential of wild-type and GFP-labeled fetal-derived neural progenitor cells before and after transplantation into the rodent hippocampus

INTRODUCTION

The hippocampal formation is a specific structure in the brain where neurogenesis occurs throughout adulthood and in which the neuronal cell loss causes various demential states. The main goal of this study was to verify whether fetal neural progenitor cells (NPCs) from transgenic rats expressing green fluorescent protein (GFP) retain the ability to differentiate into neuronal cells and to integrate into the hippocampal circuitry after transplantation.

METHODS

NPCs were isolated from E14 (gestational age: 14 days postconception) transgenic-Lewis and wild-type Sprague-Dawley rat embryos. Wild-type and transgenic cells were expanded and induced to differentiate into a neuronal lineage in vitro. Immunocytochemical and electrophysiological analysis were performed in both groups. GFP-expressing cells were implanted into the hippocampus and recorded electrophysiologically 3 months thereafter. Immunohistochemical analysis confirmed neuronal differentiation, and the yield of neuronal cells was determined stereologically.

RESULTS

NPCs derived from wild-type and transgenic animals are similar regarding their ability to generate neuronal cells in vitro. Neuronal maturity was confirmed by immunocytochemistry and electrophysiology, with demonstration of voltage-gated ionic currents, firing activity, and spontaneous synaptic currents. GFP-NPCs were also able to differentiate into mature neurons after implantation into the hippocampus, where they formed functional synaptic contacts.

CONCLUSIONS

GFP-transgenic cells represent an important tool in transplantation studies. Herein, we demonstrate their ability to generate functional neurons both in vitro and in vivo conditions. Neurons derived from fetal NPCs were able to integrate into the normal hippocampal circuitry. The high yield of mature neurons generated render these cells important candidates for restorative approaches based on cell therapy.

Self-renewal induced efficiently, safely, and effective therapeutically with one regulatable gene in a human somatic progenitor cell

In the field of induced potency and fate reprogramming, it remains unclear what the best starting cell might be and to what extent a cell need be transported back to a more primitive state for translational purposes. Reprogramming a committed cell back to pluripotence to then instruct it toward a particular specialized cell type is demanding and may increase risks of neoplasia and undesired cell types. Precursor/progenitor cells from the organ of therapeutic concern typically lack only one critical attribute--the capacity for sustained self-renewal. We speculated that this could be induced in a regulatable manner such that cells proliferate only in vitro and differentiate in vivo without the need for promoting pluripotence or specifying lineage identity. As proof-of-concept, we generated and tested the efficiency, safety, engraftability, and therapeutic utility of "induced conditional self-renewing progenitor (ICSP) cells" derived from the human central nervous system (CNS); we conditionally induced self-renewal efficiently within neural progenitors solely by introducing v-myc tightly regulated by a tetracycline (Tet)-on gene expression system. Tet in the culture medium activated myc transcription and translation, allowing efficient expansion of homogeneous, clonal, karyotypically normal human CNS precursors ex vivo; in vivo, where Tet was absent, myc was not expressed, and self-renewal was entirely inactivated (as was tumorigenic potential). Cell proliferation ceased, and differentiation into electrophysiologically active neurons and other CNS cell types in vivo ensued upon transplantation into rats, both during development and after adult injury--with functional improvement and without neoplasia, overgrowth, deformation, emergence of non-neural cell types, phenotypic or genomic instability, or need for immunosuppression. This strategy of inducing self-renewal might be applied to progenitors from other organs and may prove to be a safe, effective, efficient, and practical method for optimizing insights gained from the ability to reprogram cells.

Prospectively isolated CD133/CD24-positive ependymal cells from the adult spinal cord and lateral ventricle wall differ in their long-term in vitro self-renewal and in vivo gene expression

In contrast to ependymal cells located above the subventricular zone (SVZ) of the adult lateral ventricle wall (LVW), adult spinal cord (SC) ependymal cells possess certain neural stem cell characteristics. The molecular basis of this difference is unknown. In this study, antibodies against multiple cell surface markers were applied to isolate pure populations of SC and LVW ependymal cells, which allowed a direct comparison of their in vitro behavior and in vivo gene expression profile. Isolated CD133(+)/CD24(+)/CD45(-)/CD34(-) ependymal cells from the SC displayed in vitro self-renewal and differentiation capacity, whereas those from the LVW did not. SC ependymal cells showed a higher expression of several genes involved in cell division, cell cycle regulation, and chromosome stability, which is consistent with a long-term self-renewal capacity, and shared certain transcripts with neural stem cells of the embryonic forebrain. They also expressed several retinoic acid (RA)-regulated genes and responded to RA exposure. LVW ependymal cells showed higher transcript levels of many genes regulated by transforming growth factor-β family members. Among them were Dlx2, Id2, Hey1, which together with Foxg1 could explain their potential to turn into neuroblasts under certain environmental conditions.

CD44 is associated with proliferation, rather than a specific cancer stem cell population, in cultured canine cancer cells

BACKGROUND

The cancer stem cell hypothesis proposes that tumours are maintained by a population of cancer stem cells (CSC), which must be eradicated to prevent disease relapse after treatment. Cells expressing high levels of CD44 have been identified as candidate CSC in a variety of human tumours. This study sought to investigate CD44 expression and its potential as a CSC marker in canine cancer.

METHODS

CD44 expression in several canine cancer cell lines was determined by flow cytometry. Cells with low and high levels of CD44 expression were examined for differences in growth characteristics, colony forming ability, drug sensitivity and cell cycle profile.

RESULTS

CD44(High) cells demonstrated enhanced growth and colony forming capacity, under both adherent and low-density serum free ("tumoursphere") conditions. However, no difference in sensitivity to doxorubicin was seen between the two populations. Moreover, whilst most CD44(Low) cells were in resting or G₁ growth phase, an increased proportion of CD44(High) cells were in G₂M phase of the cell cycle. Upon proliferation in culture, both populations gave rise to progeny with a full spectrum of CD44 expression.

CONCLUSION

CD44 expression is associated with proliferation in cultured canine cancer cells, but transient and fluctuating expression may limit its utility as a CSC marker.

STAT3 is essential for the maintenance of neurosphere-initiating tumor cells in patients with glioblastomas: a potential for targeted therapy?

Glioblastoma (GBM), the highest-grade form of gliomas, is the most frequent and the most aggressive. Recently, a subpopulation of cells with stem cells characteristics, commonly named "tumor-initiating stem cells" (TISCs) or "cancer stem cells" (CSCs) were identified in GBM. These cells were shown to be highly resistant to chemotherapeutic drugs and to ionizing radiations. Consequently, the knowledge of the signals that regulate the functions and survival of TISCs is crucial. In our work, we describe a neurosphere-initiating cell (NS-IC) assay to quantify TISC/CSCs from patients with GBM and show that these cells are tumorigenic in vivo. We demonstrate that the intracellular signal transducer and activator of transcription STAT3 is constitutively activated by phosphorylation preferentially on serine 727 in these cells. Moreover, we demonstrate that the selective inhibition of STAT3 by the chemical compound Stattic or by siRNA STAT3 abrogates TISC/CSC proliferation and NS-IC suggesting that self-renewal of GBM "stem-like" cells depends on the presence of STAT3 for their maintenance. Finally, we show that inhibition of STAT3 by Stattic sensitizes TISC/CSCs to the inhibitory action of Temozolomide with a strong synergistic effect of both drugs. Overall, these results suggest that strategies focused on STAT3 inhibition are efficient at the level of "stem-like" cells and could be of interest for therapeutic purposes in patients with malignant GBM.

Cancer Stem Cells and Pediatric Solid Tumors

Recently, a subpopulation of cells, termed tumor-initiating cells or tumor stem cells (TSC), has been identified in many different types of solid tumors. These TSC, which are typically more resistant to chemotherapy and radiation compared to other tumor cells, have properties similar to normal stem cells including multipotency and the ability to self-renew, proliferate, and maintain the neoplastic clone. Much of the research on TSC has focused on adult cancers. With considerable differences in tumor biology between adult and pediatric cancers, there may be significant differences in the presence, function and behavior of TSC in pediatric malignancies. We discuss what is currently known about pediatric solid TSC with specific focus on TSC markers, tumor microenvironment, signaling pathways, therapeutic resistance and potential future therapies to target pediatric TSC.

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.

CSPG is a secreted factor that stimulates neural stem cell survival possibly by enhanced EGFR signaling

Understanding how autocrine/paracrine factors regulate neural stem cell (NSC) survival and growth is fundamental to the utilization of these cells for therapeutic applications and as cellular models for the brain. In vitro, NSCs can be propagated along with neural progenitors (NPs) as neurospheres (nsphs). The nsph conditioned medium (nsph-CM) contains cell-secreted factors that can regulate NSC behavior. However, the identity and exact function of these factors within the nsph-CM has remained elusive. We analyzed the nsph-CM by mass spectrometry and identified DSD-1-proteoglycan, a chondroitin sulfate proteoglycan (CSPG), apolipoprotein E (ApoE) and cystatin C as components of the nsph-CM. Using clonal assays we show that CSPG and ApoE are responsible for the ability of the nsph-CM to stimulate nsph formation whereas cystatin C is not involved. Clonal nsphs generated in the presence of CSPG show more than four-fold increase in NSCs. Thus CSPG specifically enhances the survival of NSCs. CSPG also stimulates the survival of embryonic stem cell (ESC)-derived NSCs, and thus may be involved in the developmental transition of ESCs to NSCs. In addition to its role in NSC survival, CSPG maintains the three dimensional structure of nsphs. Lastly, CSPG's effects on NSC survival may be mediated by enhanced signaling via EGFR, JAK/STAT3 and PI3K/Akt pathways.

Among γ-secretase substrates Notch1 alone is sufficient to block neurogenesis but does not confer self-renewal properties to neural stem cells

Notch signaling pathway enhances neural stem cell characters and regulates cell fate decisions during neural development. Interestingly, besides Notch, other γ-secretase substrates such as APP, LRP2, and ErbB4 have also proven to have biological functions in neural development. We designed a unique experimental setting, combining gain-of- (expression of Notch intracellular domain, NICD) and loss-of-function (γ-secretase inhibition) methods, and were able to examine the function of Notch alone by excluding the activity of other γ-secretase substrates. Here, we show that the frequency and size of neurospheres generated from embryonic neural stem cells (NSCs) significantly decreased by 62.7% and 37.2%, respectively, in the presence of γ-secretase inhibitor even when NICD was expressed. Under the condition of differentiation, however, the γ-secretase inhibitor treatment did not influence the promotion of astrogenesis at the expense of neurogenesis by NICD. These results indicate that other γ-secretase substrate(s) along with Notch are important in the maintenance of the stemness of NSCs, but that Notch alone can sufficiently inhibit neurogenesis without the action of the other γ-secretase substrates during differentiation.

Cancer stem cells in the central nervous system--a critical review

The cancer stem cell hypothesis postulates that tumors arise from, and are maintained by, a small subpopulation of cancer stem cells. This concept has recently become increasingly controversial, following a series of conflicting results. The cell-surface epitope CD133 has been proposed as a brain cancer stem cell marker, whereas a growing number of studies clearly show a tumorigenic potential among CD133(-) cells as well. Diverging results suggest that assays for isolating cancer stem cells impose a selection bias on which cells are defined as cancer stem cells. Here, we highlight some recent developments, with an emphasis on reports that call for caution in the acceptance of the brain cancer stem cell hypothesis.

Development of cell-processing systems for human stem cells (neural stem cells, mesenchymal stem cells, and iPS cells) for regenerative medicine

Regenerative medicine using human stem cells is one of the newest and most promising fields for treating various intractable diseases and damaged organs. For clinical applications, choosing which human stem cells to use, i.e. according to tissue of origin and progenitor type, is a critical issue. Neural stem/progenitor cells (NSPCs) hold promise for treating various neurological diseases. We have shown that the transporter protein ABCB1 is predominantly expressed in immature human fetal NSPCs, and thus could be used as a phenotypic marker to investigate and monitor NSPCs in culture. We describe our proposed model for the in vitro proliferative process of aggregated human NSPCs and show that neurosphere enlargement and NSPC proliferation are mutually reinforcing. We have established that human neurospheres contain a heterogeneous cell population, knowledge that will contribute to the development of human neurospheres with desirable characteristics for clinical applications. Furthermore, decidua-derived mesenchymal cells (DMCs), which we isolated from human placenta, have unique properties as mesenchymal stem cells. They also generate a pericellular matrix (PCM-DM) that supports the growth and pluripotency of human embryonic stem cells and induced pluripotent stem cells (hiPS) cells. The newly developed re-programming techniques for generating hiPS cells should greatly contribute to cell therapies using human pluripotent stem cells, including those derived from DMCs. Our DMC-derived hiPS cells are a promising candidate source of allogeneic hiPS cells for clinical applications. We hope our findings will contribute to the development of cell-culture systems for generating human allogeneic stem cells for clinical use in regenerative medicine.

Id proteins facilitate self-renewal and proliferation of neural stem cells

Members of helix-loop-helix (HLH) protein family of Id (inhibitor of differentiation) dimerize with bHLH transcription factors and function as negative regulators of differentiation during development. Most of inhibitory roles of Id proteins have been demonstrated in non-neural tissues, and their roles in the developing nervous system are not clearly demonstrated. In this study, we show that Id1, Id2, and Id3 increase self-renewing and proliferation potential of cortical neural stem cells (NSCs) while inhibiting neuronal differentiation. In electrophoretic mobility gel shift and luciferase assays, Id proteins interfered with binding of NeuroD/E47 complexes to the E-box sequences and inhibited E-box-mediated gene expression. Overexpression of Id proteins in NSCs increased both the number and the size of neurospheres in colony-forming assays. Expression of Hes1 and Hes5 was not increased by overexpression of Id proteins under the condition in which Nestin expression was increased. In utero electroporation of Id yielded higher numbers of Ki67-positive and Sox2-positive cells in the mouse embryonic brain. The study suggests Id proteins play independent roles in the maintenance of neural stem properties.

Effects of hypoxia on expression of a panel of stem cell and chemoresistance markers in glioblastoma-derived spheroids

Tumor hypoxia has been attributed to play a crucial role in tumorigenesis and therapeutic resistance. Recently, it has been suggested that hypoxia leads to and maintains the undifferentiated state of tumor stem cells, thereby contributing to chemoresistance. The aim of the present study is to investigate the influence of hypoxia on the protein expression of a panel of stem cell and chemoresistance markers using in vivo-like multicellular tumor spheroids derived from a glioblastoma short-term culture with tumor stem cell properties (SJ-1) as well as a conventional glioblastoma cell line (U87). Spheroids were formed in 21% and 1% O(2) in serum-free medium. The immunohistochemical panel included hypoxia (HIF-1α, HIF-2α), proliferation (Ki-67), and stem cell markers (CD133, podoplanin, Bmi-1, nestin, Sox-2) as well as markers related to chemoresistance (MGMT, TIMP-1, Lamp-1, MRP1, MDR-1). As spheroids derived in hypoxia were smaller than in normoxia, a set of experiments was included in which the culturing time of hypoxic spheroids was extended to obtain equally sized spheroids. The results showed that expression of HIF-1α and HIF-2α was increased in hypoxia, whereas Ki-67 was reduced. Expression of stem cell markers CD133, podoplanin, Bmi-1, and nestin was increased in hypoxia, whereas Sox-2 was increased in SJ-1 only. TIMP-1 and Lamp-1 were increased in both SJ-1 and U87. In conclusion, the tumor cell phenotype related to stemness, and thereby potentially to chemoresistance, seems to depend on the oxygen tension, suggesting that development of therapeutic strategies targeting tumor stem cells should take oxygen tension into account.

Individual cell movement, asymmetric colony expansion, rho-associated kinase, and E-cadherin impact the clonogenicity of human embryonic stem cells

Clonality is, at present, the only means by which the self-renewal potential of a given stem cell can be determined. To assess the clonality of human embryonic stem cells (hESC), a protocol involving seeding wells at low cell densities is commonly used to surmount poor cloning efficiencies. However, factors influencing the accuracy of such an assay have not been fully elucidated. Using clonogenic assays together with time-lapse microscopy, numerical analyses, and regulated gene expression strategies, we found that individual and collective cell movements are inherent properties of hESCs and that they markedly impact the accuracy of clonogenic assays. Analyses of cell motility using mean-square displacement and paired migration correlation indicated that cell movements become more straight-line or ballistic and less random-walk as separation distance decreases. Such motility-induced reaggregation (rather than a true clone) occurs approximately 70% of the time if the distance between two hESCs is <6.4 mum, and is not observed if the distance is >150 mum. Furthermore, newly formed small hESC colonies have a predisposition toward the formation of larger colonies through asymmetric colony expansion and movement, which would not accurately reflect self-renewal and proliferative activity of a true hESC clone. Notably, inhibition of Rho-associated kinase markedly upregulated hESC migration and reaggregation, producing considerable numbers of false-positive colonies. Conversely, E-cadherin upregulation significantly augmented hESC clonogenicity via improved survival of single hESCs without influencing cell motility. This work reveals that individual cell movement, asymmetric colony expansion, Rho-associated kinase, and E-cadherin all work together to influence hESC clonogenicity, and provides additional guidance for improvement of clonogenic assays in the analysis of hESC self-renewal.

The utility and limitations of neurosphere assay, CD133 immunophenotyping and side population assay in glioma stem cell research

The newly proposed glioma stem cell (GSC) hypothesis may re-model the way we diagnose and treat the tumor, which highlights the need for a complete knowledge on the genetic and epigenetic "blueprints" of GSCs. To identify the true "stemness" signatures, pure GSC populations are primarily needed. Reliable in vitro methods enriching for GSCs and thereby identifying the key stem-like characteristics constitute the preliminary step forward. We discuss in this review the current widely used methods for enriching and isolating GSCs, namely neurosphere assay, CD133 Immunophenotyping and side population assay, and detail their limitations and potential pitfalls that could complicate interpretation of corresponding results.

Cancer stem cells: cell culture, markers, and targets for new therapies

A cancer stem cell (CSC) is defined as an undifferentiated cell with the ability to self-renew, differentiate to multiple lineages and initiate tumors that mimic the parent tumor. In this review, we focus on glioblastomas, describing recent progress and problems in characterizing these cells. There have been advances in CSC culture, but tumor cell heterogeneity has made purification of CSCs difficult. Indeed, it may be that CSCs significantly vary from tumor to tumor. We also discuss the proposal that CSCs are resistant to radiotherapy and chemotherapy and play a major role in repopulating tumors following treatment. To overcome their resistance to conventional therapies, we may be able to use our extensive knowledge of the signaling pathways essential for stem cells during development. These pathways have potential as targets for new glioblastoma therapies. Hence, although there is an ongoing debate on the nature of CSCs, the theory continues to suggest new ideas for both the lab and the clinic.

Bone morphogenetic protein 4 stimulates attachment of neurospheres and astrogenesis of neural stem cells in neurospheres via phosphatidylinositol 3 kinase-mediated upregulation of N-cadherin

The neurosphere culture system is useful for expanding neural stem cells (NSCs) without affecting self-renewal potential and multipotency. However, the extrinsic signals that affect the formation or dissociation of neurospheres are poorly understood. Here, we found that bone morphogenetic protein 4 (BMP4) induced the attachment of neurospheres, astrocytic differentiation, and migration of neurosphere NSCs. These outcomes were accompanied by Akt activation and upregulation of the adhesion molecule, N-cadherin. A phosphatidylinositol 3 kinase (PI3 kinase) inhibitor (LY294002) blocked attachment of neurosphere, astrocytic differentiation, migration, and N-cadherin upregulation of neurosphre NSCs. The PI3 kinase-Akt pathway appeared to selectively mediate the effects of BMP4, as neurosphere attachment was unaffected by MEK inhibitors (PD98059 and U0126). Importantly, a neutralizing N-cadherin antibody inhibited BMP4-induced neurosphere attachment, astrocytic differentiation, and migration of neurosphere NSCs. Together, these findings show that BMP4-induced attachment of neurospheres is related to the astrocytic differentiation of these cells and that these effects are attributable, at least in part, to PI3 kinase-Akt pathway-dependent induction of N-cadherin.

Taurine stimulates proliferation of mice embryonic cultured neural progenitor cells

Taurine is present in high levels in fetal brain which decrease in the adult, suggesting its role in brain development. In some regions of taurine deficient animals cells show defective migration and the presence of numerous mitotic figures, suggesting a delay in cell proliferation. To know more about the role of taurine in the developing brain cells, the present study investigated whether taurine is a factor involved in proliferation or/and viability of neural progenitor cells (NPC). NPC were obtained from 13.5-days mice embryos mesencephalon, and cultured during 4-5 days to form neurospheres in the presence of EGF plus FGFb (EGF/FGF) or EGF alone. Mesencephalon taurine content (349 mmoles/kg protein) was lost in NPC and recovered after addition of 10 mM taurine to the culture. Neurospheres-forming NPC were over 94% nestin-positive. Taurine increased 38.6% and 43.2% the number of NPC formed in EGF/FGF or EGF conditions, respectively. In secondary neurospheres this increase was 24.6% and 62.1%, in EGF/FGF or EGF cultures respectively. Correspondingly neurospheres size was increased by taurine but neurospheres number was not enhanced. Taurine significantly increased the number of BrdU-positive cells, without affecting cell viability, suggesting proliferation as the mechanism responsible for taurine action increasing NPC. Taurine seems unable to increase the number of beta-III-tubulin-positive cells differentiated from neurospheres after serum addition, and rather an increase in astrocytes was observed. These results point to taurine as a trophic factor contributing to optimize NPC proliferation.

Regulation of FGF1 gene promoter through transcription factor RFX1

Fibroblast growth factor 1 (FGF1) has been suggested to have an important role in cell growth, proliferation, and neurogenesis. Human FGF1 gene 1B promoter (-540 to +31)-driven green fluorescence (F1BGFP) has been shown to monitor endogenous FGF1 expression. F1BGFP could also be used to isolate neural stem/progenitor cells from embryonic, neonatal, and adult mouse brains or to isolate glioblastoma stem cells (GBM-SCs) from human glioblastoma tissues. Here, we present evidence that transcription factor RFX1 could bind the 18-bp cis-elements (-484 to -467) of the F1B promoter, modulate F1BGFP expression and endogenous FGF1 expression, and further regulate the maintenance of GBM-SCs. These observations were substantiated by using yeast one-hybrid assay, electrophoretic mobility shift assay, chromatin immunoprecipitation assay, gain- and loss-of-function assays, and neurosphere assays. Overexpression of RFX1 was shown to down-regulate FGF-1B mRNA expression and neurosphere formation in human glioblastoma cells, whereas RNA interference knockdown of RFX1 demonstrated the opposite effects. Our findings provide insight into FGF1 gene regulation and suggest that the roles of FGF1 and RFX1 in the maintenance of GBM-SCs. RFX1 may negatively regulate the self-renewal of GBM-SCs through modulating FGF-1B and FGF1 expression levels by binding the 18-bp cis-elements of the F1B promoter.

Human prostate sphere-forming cells represent a subset of basal epithelial cells capable of glandular regeneration in vivo

BACKGROUND

Prostate stem/progenitor cells function in glandular development and maintenance. They may be targets for tumor initiation, so characterization of these cells may have therapeutic implications. Cells from dissociated tissues that form spheres in vitro often represent stem/progenitor cells. A subset of human prostate cells that form prostaspheres were evaluated for self-renewal and tissue regeneration capability in the present study.

METHODS

Prostaspheres were generated from 59 prostatectomy specimens. Lineage marker expression and TMPRSS-ERG status was determined via immunohistochemistry and fluorescence in situ hybridization (FISH). Subpopulations of prostate epithelial cells were isolated by cell sorting and interrogated for sphere-forming activity. Tissue regeneration potential was assessed by combining sphere-forming cells with rat urogenital sinus mesenchyme (rUGSM) subcutaneously in immunocompromised mice.

RESULTS

Prostate tissue specimens were heterogeneous, containing both benign and malignant (Gleason 3-5) glands. TMPRSS-ERG fusion was found in approximately 70% of cancers examined. Prostaspheres developed from single cells at a variable rate (0.5-4%) and could be serially passaged. A basal phenotype (CD44+CD49f+CK5+p63+CK8-AR-PSA-) was observed among sphere-forming cells. Subpopulations of prostate cells expressing tumor-associated calcium signal transducer 2 (Trop2), CD44, and CD49f preferentially formed spheres. In vivo implantation of sphere-forming cells and rUGSM regenerated tubular structures containing discreet basal and luminal layers. The TMPRSS-ERG fusion was absent in prostaspheres derived from fusion-positive tumor tissue, suggesting a survival/growth advantage of benign prostate epithelial cells.

CONCLUSION

Human prostate sphere-forming cells self-renew, have tissue regeneration capability, and represent a subpopulation of basal cells.

Isolation of clonogenic, long-term self renewing embryonic renal stem cells

A tissue stem cell should exhibit long-term self-renewal, clonogenicity and a capacity to differentiate into the tissue of origin. Such a postnatal renal stem cell has not been formally identified. The metanephric mesenchyme (MM) of the developing kidney gives rise to both the renal interstitium and the nephrons and is regarded as the progenitor population of the developing kidney. However, isolated MM does not self renew and requires immortalization for survival in culture. Here we report the isolation and sustained culture of long-term repopulating, clonal progenitors from the embryonic kidney as free floating nephrospheres. Such cells displayed clonal self renewal for in excess of twenty passages when cultured with bFGF and thrombin, showed broad mesodermal multipotentiality, but retained expression of key renal transcription factors (Wt1, Sall1, Eya1, Six1, Six2, Osr1 and Hoxa11). While these cells did display limited capacity to contribute to developing embryonic kidney explants, nephrospheres did not display in vitro renal epithelial capacity. Nephrospheres could be cultured from both Sall1(+) and Sall1(-) fractions of embryonic kidney, suggesting that they were derived from the MM as a whole and not specifically the MM-derived cap mesenchyme committed to nephron formation. This embryonic renal stem cell population was not able to be isolated from postnatal kidney confirming that while the embryonic MM represents a mulitpotent stem cell population, this does not persist after birth.

A hierarchy of endothelial colony-forming cell activity displayed by bovine corneal endothelial cells

PURPOSE

To test the hypothesis that the robust expansion of bovine corneal endothelial cells (BCECs) in vitro is due to the presence of individual endothelial cells with various levels of proliferative potential.

METHODS

BCECs and bovine vascular endothelial cells (ECs) derived from aorta, coronary artery, and pulmonary artery were cultivated in optimized medium. These cell populations were confirmed by morphologic features, functional assays, and gene expression profiles. Moreover, ECs were plated in a single-cell clonogenic assay to evaluate colony-forming ability.

RESULTS

Both corneal and vascular ECs were confirmed to be pure populations of endothelium uncontaminated with hematopoietic cells. A complete hierarchy of endothelial colony-forming cells (ECFCs) was identified in BCECs by a single-cell clonogenic assay. The distribution of the various types of ECFCs was similar to the control ECs removed from the systemic vessels.

CONCLUSIONS

Cultured BCECs display clonal proliferative properties similar to those of vascular ECs.