Musashi1: an evolutionally conserved marker for CNS progenitor cells including neural stem cells

her5 expression reveals a pool of neural stem cells in the adult zebrafish midbrain

Current models of vertebrate adult neural stem cells are largely restricted to the rodent forebrain. To extract the general mechanisms of neural stem cell biology, we sought to identify new adult stem cell populations, in other model systems and/or brain areas. The teleost zebrafish appears to be an ideal system, as cell proliferation in the adult zebrafish brain is found in many more niches than in the mammalian brain. As a starting point towards identifying stem cell populations in this system, we used an embryonic neural stem cell marker, the E(spl) bHLH transcription factor Her5. We demonstrate that her5 expression is not restricted to embryonic neural progenitors, but also defines in the adult zebrafish brain a new proliferation zone at the junction between the mid- and hindbrain. We show that adult her5-expressing cells proliferate slowly, self-renew and express neural stem cell markers. Finally, using in vivo lineage tracing in her5:gfp transgenic animals, we demonstrate that the her5-positive population is multipotent, giving rise in situ to differentiated neurons and glia that populate the basal midbrain. Our findings conclusively identify a new population of adult neural stem cells, as well as their fate and their endogenous environment, in the intact vertebrate brain. This cell population, located outside the forebrain, provides a powerful model to assess the general mechanisms of vertebrate neural stem cell biology. In addition, the first transcription factor characteristic of this cell population, Her5, points to the E(Spl) as a promising family of candidate adult neural stem cell regulators.

Distinct Population of Hair Cell Progenitors Can Be Isolated from the Postnatal Mouse Cochlea Using Side Population Analysis

In mammals, the permanence of hearing loss is due mostly to the incapacity of the cochlea to replace lost mechano-receptor cells (i.e., hair cells [HCs]). The generation of new HCs from a renewable source of progenitors is a principal requirement for developing a cell therapy within this sensory organ. A subset of stem cells, termed side population (SP), has been identified in several tissues of mammals. The ATP-binding cassette transporter Abcg2/Bcrp1 contributes to the specification of the SP phenotype and is proposed as a universal marker for stem/progenitor cells. A defining character of these SP cells is a high efflux capacity for Hoechst dye. Here, we demonstrate that Abcg2 transporter is expressed with two other stem/progenitor cell markers (i.e., Nestin and Musashi1) in distinct and overlapping domains of the supporting cells within the postnatal cochlea. We have developed and describe a fluorescence-activated cell sorting (FACS) technique that enables the purification of a discrete subpopulation of SP-supporting cells from the early postnatal mouse cochlea based on their ability to exclude Hoechst dye. These FACS-isolated cells can divide and express markers of stem/progenitor cells such as Abcg2, a determinant of the SP phenotype, and Musashi1, a neural stem/progenitor cell marker. These markers can differentiate cells expressing markers of HCs and supporting cells in vitro. Our observation that these SP cells are capable of differentiating into HC-like cells implies a possible use for such cells (i.e., the replacement of lost auditory HCs within damaged cochlea).

Differential developmental ability of embryos cloned from tissue-specific stem cells

Although cloning animals by somatic cell nuclear transfer is generally inefficient, the use of certain nuclear donor cell types may significantly improve or deteriorate outcomes. We evaluated whether two multipotent stem cell lines produced in vitro--neural stem cells (NSCs) and mesenchymal stem cells (MSCs)--could serve as nuclear donors for nuclear transfer cloning. Most (76%) NSC-derived embryos survived the two-cell-to-four-cell transition, the stage when the major zygotic gene activation occurs. Consistent with this observation, the expression patterns of zygotically active genes were better in NSC-derived embryos than in fibroblast clone embryos, which arrested at the two-cell stage more frequently. Embryo transfer experiments demonstrated that at least some of these NSC embryos had the ability to develop to term fetuses (1.6%, 3/189). In contrast, embryos reconstructed using MSCs showed a low rate of in vitro development and never underwent implantation in vivo. Chromosomal analysis of the donor MSCs revealed very frequent aneuploidy, which probably impaired the potential for development of their derived clones. This is the first demonstration that tissue-specific multipotent stem cells produced in vitro can serve as donors of nuclei for cloning mice; however, these cells may be prone to chromosomal aberrations, leading to high embryonic death rates. We found previously that hematopoietic stem cells (HSCs) are very inefficient donor cells because of their failure to activate the genes essential for embryonic development. Taken together, our data led us to conclude that tissue-specific stem cells in mice, namely NSCs, MSCs, and HSCs, exhibited marked variations in the ability to produce cloned offspring and that this ability varies according to both the epigenetic and genetic status of the original genomes. Disclosure of potential conflicts of interest is found at the end of this article.

Enhanced therapeutic efficacy of oncolytic herpes vector G207 against human non-small cell lung cancer--expression of an RNA-binding protein, Musashi1, as a marker for the tailored gene therapy

BACKGROUND

Oncolytic herpes vectors like G207 have shown considerable promise in the treatment of solid tumors, but their potency must be enhanced for the full achievement of therapeutic efficacy. Deletion of the innate gamma34.5 gene made these vectors extremely safe, but their efficacy was also severely attenuated. Use of tumor-specific promoters is one method to direct toxicity and enhance efficacy against tumors. Recently, Musashi1 has been shown expressed in some tumor tissues.

METHODS

Eleven human cancer cell lines including five non-small cell lung cancers (NSCLCs) were investigated. Musashi1 mRNA expression was examined by RT-PCR analysis. Western blotting was also performed. Transcriptional activity of P/musashi1 in NSCLCs was assayed by GFP reporter plasmids. Then we constructed a defective amplicon vector containing musashi1 promoter/ICP34.5 with G207 as helper virus (dvM345). In vitro cytotoxicity against NSCLCs and growth characteristics of helper virus were examined. A Lu-99 subcutaneous tumor model was used in an animal study. The tumor volume treated with G207 alone or dvM345 was measured.

RESULTS

Musashi1 mRNA was detected in four cell lines. Two in five NSCLCs were positive, and P/musashi1 was proved functional within them. Against these cell lines, dvM345 showed enhanced cytotoxicity, and helper viral growth was augmented. A subcutaneous tumor study confirmed the enhanced therapeutic efficacy of G207 by dvM345 without compromising safety.

CONCLUSIONS

These results suggest that Musashi1 might be involved in the development of several carcinomas including NSCLC. In the context of oncolytic herpes vector strategy, the P/musashi1-ICP34.5 method could be used for the treatment of cancers expressing Musashi1.

Transcription profiling of adult and fetal human neuroprogenitors identifies divergent paths to maintain the neuroprogenitor cell state

Global gene expression profiling was performed using RNA from adult human hippocampus-derived neuroprogenitor cells (NPCs) and multipotent frontal cortical fetal NPCs compared with adult human mesenchymal stem cells (hMSCs) as a multipotent adult stem cell control, and adult human hippocampal tissue, to define a gene expression pattern that is specific for human NPCs. The results were compared with data from various databases. Hierarchical cluster analysis of all neuroectodermal cell/tissue types revealed a strong relationship of adult hippocampal NPCs with various white matter tissues, whereas fetal NPCs strongly correlate with fetal brain tissue. However, adult and fetal NPCs share the expression of a variety of genes known to be related to signal transduction, cell metabolism and neuroectodermal tissue. In contrast, adult NPCs and hMSCs overlap in the expression of genes mainly involved in extracellular matrix biology. We present for the first time a detailed transcriptome analysis of human adult NPCs suggesting a relationship between hippocampal NPCs and white matter-derived precursor cells. We further provide a framework for standardized comparative gene expression analysis of human brain-derived NPCs with other stem cell populations or differentiated tissues. Disclosure of potential conflicts of interest is found at the end of this article.

Enhancement of susceptibility of adult mouse brain to cytomegalovirus infection by infusion of epidermal growth factor

Neural precursor cells, including neural stem and progenitor cells, in the subventricular zone (SVZ) are the main targets for cytomegalovirus (CMV) infection in developing brains. The neural precursor cells in the SVZ of the adult brain have been reported to respond by proliferating after infusion with epidermal growth factor (EGF). Here we report the susceptibility of the precursor cells in the adult mouse brain to murine CMV (MCMV) infection. Adult mouse brains from 10-, 25-, and 70-week-old (W) mice were infused with either phosphate-buffered saline or EGF into the brain for 3 days, and then intracerebrally infected with MCMV for 5 days. The susceptibility of the adult brains to MCMV was significantly increased by infusion of EGF in terms of viral titers and viral antigen-positive cells. The susceptibility of the young adult brain from 10-week-old mice to MCMV was higher than that of the adult brains from 25-week-old or 70-week-old mice. Both the ependymal and the SVZ cells were susceptible to MCMV infection. The number of virus-infected cells in the SVZ was significantly increased by infusion of EGF, whereas the number of infected ependymal cells was not significantly increased. Among the virus-infected cells in the SVZ, 73% were positive for nestin, 87% were positive for Musashi, 86% were positive for GFAP, and 96% were positive for PCNA. These results indicate that the susceptibility of the adult brain to MCMV is correlated with the proliferative ability of the neural precursor cells in the SVZ of the adult brain.

Expression of the Neural RNA-binding protein Musashi1 in pediatric brain tumors

Musashi1 (MSI1) is an evolutionarily conserved RNA-binding protein, selectively expressed in neural stem cells (NSCs) and considered a versatile marker for normal NSCs and tumor cell diagnosis. Here, we examined MSI1 expression in primary pediatric brain tumors, medulloblastomas and ependymomas, by double immunostaining with lineage phenotypic markers (Lin). These tumors highly express MSI1 and are heterogeneous, containing both MSI1+/Lin- tumor cells in regions of relatively high cellularity and proliferative activity and MSI1+/Lin+ tumor cells in regions of lower cellularity. These findings suggest that MSI1 may be a useful marker for characterizing tumor heterogeneity and for examining in situ the analogy between normal NSCs and MSI1+ cells in pediatric brain tumors. This test could be easily applied to routine clinical diagnosis.

Multipotent cells from mammalian iris pigment epithelium

The regeneration of lens tissue from the iris of newts has become a classical model of developmental plasticity, although little is known about the corresponding plasticity of the mammalian iris. We here demonstrate and characterize multipotent cells within the iris pigment epithelium (IPE) of postnatal and adult rodents. Acutely-isolated IPE cells were morphologically homogeneous and highly pigmented, but some produced neurospheres which expressed markers characteristic of neural stem/progenitor cells. Stem/progenitor cell markers were also expressed in the IPE in vivo both neonatally and into adulthood. Inner and outer IPE layers differentially expressed Nestin (Nes) in a manner suggesting that they respectively shared origins with neural retina (NR) and pigmented epithelial (RPE) layers. Transgenic marking enabled the enrichment of Nes-expressing IPE cells ex vivo, revealing a pronounced capacity to form neurospheres and differentiate into photoreceptor cells. IPE cells that did not express Nes were less able to form neurospheres, but a subset initiated the expression of pan-neural markers in primary adherent culture. These data collectively suggest that discrete populations of highly-pigmented cells with heterogeneous developmental potencies exist postnatally within the IPE, and that some of them are able to differentiate into multiple neuronal cell types.

N-cadherin mediates cortical organization in the mouse brain

The cerebral cortex is a complex laminated structure generated by the sequential migration of developing neurons from the ventricular zone. One of the molecules that may play a role in cortical morphogenesis is N-cadherin since its blocking causes disruption of the ordered arrangement of cells in other neural tissues, such as the neural retina. Here, we show that when the N-cadherin gene had been conditionally deleted in the mouse cerebral cortex, the intra-cortical structures were nearly completely randomized; e.g., mitotic cells and postmitotic cells were scattered throughout the cortex without any order. These defects seemed to mainly originate from the disruption of the adherens junctions (AJs) localized in the apical end of neuroepithelial cells, where N-cadherin is normally most highly concentrated. In the absence of N-cadherin, neuroepithelial or radial glial cells could not expand their bodies or processes to span the distance between the ventricular and pial surfaces and therefore terminated them in the middle zone of the cortex. These results demonstrate that N-cadherin is essential for maintaining the normal architecture of neuroepithelial or radial glial cells and that their disruption randomizes the internal structures of the cortex.

Human cytomegalovirus inhibits neuronal differentiation and induces apoptosis in human neural precursor cells

Human cytomegalovirus (HCMV) is the most common cause of congenital infections in developed countries, with an incidence varying between 0.5 and 2.2% and consequences varying from asymptomatic infection to lethal conditions for the fetus. Infants that are asymptomatic at birth may still develop neurological sequelae, such as hearing loss and mental retardation, at a later age. Infection of neural stem and precursor cells by HCMV and consequent disruption of the proliferation, differentiation, and/or migration of these cells may be the primary mechanism underlying the development of brain abnormalities. In the present investigation, we demonstrate that human neural precursor cells (NPCs) are permissive for HCMV infection, by both the laboratory strain Towne and the clinical isolate TB40, resulting in 55% and 72% inhibition of induced differentiation of human NPCs into neurons, respectively, when infection occurred at the onset of differentiation. This repression of neuronal differentiation required active viral replication and involved the expression of late HCMV gene products. This capacity of HCMV to prevent neuronal differentiation declined within 24 h after initiation of differentiation. Furthermore, the rate of cell proliferation in infected cultures was attenuated. Surprisingly, HCMV-infected cells exhibited an elevated frequency of apoptosis at 7 days following the onset of differentiation, at which time approximately 50% of the cells were apoptotic at a multiplicity of infection of 10. These findings indicate that HCMV has the capacity to reduce the ability of human NPCs to differentiate into neurons, which may offer one explanation for the abnormalities in brain development associated with congenital HCMV infection.

Postischemic exercise decreases neurogenesis in the adult rat dentate gyrus

Running exercise enhances neurogenesis in the normal adult and aged hippocampus. However, the effect of exercise on neurogenesis in the ischemic hippocampus is unclear. Here, we show that running exercise has different effects on ischemic and non-ischemic brain. Young (3-4-month-old) normotensive Wistar rats were used for this study. We administered bromodeoxyuridine (BrdU) to rats 7 days after the induction of transient forebrain ischemia or sham operation. BrdU-labeled cells were increased in the ischemic subgranular zone (SGZ) and granule cell layer (GCL) and double immunofluoresence showed approximately 80% of BrdU-labeled cells expressed neuronal markers. To assess the effect of running exercise on neurogenesis, BrdU-labeled cells in these regions were quantified after 1 day and 14 days. In sham-operated rats, the numbers of BrdU-labeled cells were significantly increased (2.2-fold) in the SGZ and GCL in response to running exercise. The numbers of BrdU-labeled cells were increased in response to ischemia, however, they were decreased 14 days after BrdU administration and running exercise accelerated the reduction in BrdU-labeled cells in ischemic rats. These findings suggest that running exercise has a negative effect on neurogenesis in the ischemic hippocampus. This may be important with respect to assessment of therapeutic approaches for functional recovery after stroke.

Stem/progenitor cell-specific enhanced green fluorescent protein expression driven by the endogenous Mcm2 promoter

Previous studies have demonstrated expression of the minichromosome maintenance protein Mcm2 in cells that remain competent to divide, including stem/progenitor cells of the subventricular zone (SVZ) within the brain. Here, a transgenic mouse line in which the Mcm2 gene drives expression of enhanced green fluorescent protein (EGFP) was constructed by insertion of an internal ribosomal entry site (IRES)-EGFP cassette into the last exon of the gene, 3' to the stop codon. In these mice, expression of EGFP is observed in the SVZ and several other tissues with high proliferative activity, including the spleen, intestine, hair follicles, and bone marrow. These observations suggest that EGFP fluorescence in this mouse line provides an index of the proliferative capacity of different tissues. Immunohistological analysis demonstrates a direct concordance between expression of EGFP and Mcm2, consistent with a transcriptional level downregulation of Mcm2 expression in postmitotic cells. To test the utility of EGFP expression for recovery of live cells retaining the capacity to divide, EGFP-expressing and -nonexpressing cells from bone marrow and brain were isolated from an adult Mcm2(IRES-EGFP) mouse by fluorescence-activated cell sorting and assayed for clonal growth. The EGFP-positive fraction contained the entire clonogenic population of the bone marrow and greater than 90% of neurosphere-forming cells from the brain. Brain-derived clonogenic cells were shown to remain competent to differentiate towards all three neural lineages. These studies demonstrate that the Mcm2(IRES-EGFP) transgenic line constructed here can be used for recovery of proliferation competent cells from different tissue types.

Leukotriene B4 and lipoxin A4 are regulatory signals for neural stem cell proliferation and differentiation

Leukotrienes (LTs) and lipoxins (LXs) are lipid mediators that play a key role in regulating acute inflammatory responses. Their roles in neural stem cell (NSC) functions are of interest. We showed here that LTB(4) and LXA(4) regulated proliferation and differentiation of murine NSCs that were isolated from embryo brains. Proliferation of NSCs was stimulated by LTB(4) (3 to 100 nM) and blocked by receptor antagonist (IC(50)=2.7 microM). In contrast, LXA(4), and its aspirin-triggered-15-epi-LXA(4) stable analog attenuated growth of NSCs at as little as 1 nM. Both lipoxygenase (LOX) inhibitors and LTB(4) receptor antagonists caused apoptosis and cell death. Gene chip analysis revealed that growth-related gene expressions such as epidermal growth factor (EGF) receptor, cyclin E, p27, and caspase 8 were tightly regulated by LTB(4); LXA(4) gave the opposite gene expressions. In addition to proliferation, LTB(4) induced differentiation of NSCs into neurons as monitored by neurite outgrowth and MAP2 expression. These results indicate for the first time that LTB(4) and LXA(4) directly regulate proliferation and differentiation of NSCs, suggesting these new pathways may be useful in restoring stem cells.

Integrins are markers of human neural stem cells

The identification of markers for the isolation of human neural stem cells (hNSCs) is essential for studies of their biology and therapeutic applications. This study investigated expression of the integrin receptor family by hNSCs as potential markers. Selection of alpha6(hi) or beta1(hi) cells by fluorescence-activated cell sorting led to an enrichment of human neural precursors, as shown by both neurosphere forming assays and increased expression of prominin-1, sox2, sox3, nestin, bmi1, and musashi1 in the beta1(hi) population. Cells expressing high levels of beta1 integrin also expressed prominin-1 (CD133), a marker previously used to isolate hNSCs, and selection using integrin beta1(hi) cells or prominin-1(hi) cells was found to be equally effective at enriching for hNSCs from neurospheres. Therefore, integrin subunits alpha6 and beta1 are highly expressed by human neural precursors and represent convenient markers for their prospective isolation.

Reg I-knockout mice reveal its role in regulation of cell growth that is required in generation and maintenance of the villous structure of small intestine

Reg I (regenerating gene product I) is a growth factor that plays a central role in the generation and regeneration of the gastric mucosal architecture. On the other hand, mouse Reg I mRNA is expressed at the highest levels in the small intestine among the gastrointestinal tissues. In the current study, with the aim to clarify the role of Reg I protein in the small intestine, the temporal and spatial pattern of Reg I expression and the phenotype of Reg I-knockout mice in the tissue were examined. In the wild-type mice, immunohistochemistry localized Reg I protein expression in absorptive cells located in the lower half of the intestinal villi. Reg I expression was undetectable until embryonic day 13 (E13), when the fetal intestine still lacks villous structure; however, it dramatically increased at E17 along with the formation and maturation of the fetal intestinal villi. In the small intestine of the adult Reg I-knockout mice, less densely packed, round-shaped aberrant morphology of the absorptive cells was observed light microscopically, and electron microscopical examination revealed a strikingly loose connection of these cells to the basement membrane. Antiproliferating cell nuclear antigen staining and anti-Ki67 staining demonstrated the marked decrease in the number of proliferating cells in the small intestinal mucosa of the knockout mice. The cell migration speed visualized by one shot labeling of 5-bromodeoxyuridine was significantly slower in the knockout mice. These phenotypes of Reg I-knockout mice emerged, in accordance with the temporal pattern of Reg I expression described above, from E17. Reg I was considered to be a regulator of cell growth that is required to generate and maintain the villous structure of the small intestine.

Postnatal cellular contributions of the hippocampus subventricular zone to the dentate gyrus, corpus callosum, fimbria, and cerebral cortex

The rodent dentate gyrus (DG) is formed in the embryo when progenitor cells migrate from the dentate neuroepithelium to establish a germinal zone in the hilus and a secondary germinal matrix, near the fimbria, called the hippocampal subventricular zone (HSVZ). The developmental plasticity of progenitors within the HSVZ is not well understood. To delineate the migratory routes and fates of progenitors within this zone, we injected a replication-incompetent retrovirus, encoding the enhanced green fluorescent protein (EGFP), into the HSVZ of postnatal day 5 (P5) mice. Between P6 and P45, retrovirally-infected EGFP(+) of progenitors migrated into the DG, established a reservoir of progenitor cells, and differentiated into neurons and glia. By P6-7, EGFP(+) cells were observed migrating into the DG. Subsets of these EGFP(+) cells expressed Sox2 and Musashi-1, characteristic of neural stem cells. By P10, EGFP(+) cells assumed positions within the DG and expressed immature neuronal markers. By P20, many EGFP(+) cells expressed the homeobox prospero-like protein Prox1, an early and specific granule cell marker in the CNS, and extended mossy fiber projections into the CA3. A subset of non-neuronal EGFP(+) cells in the dentate gyrus acquired the morphology of astrocytes. Another subset included EGFP(+)/RIP(+) oligodendrocytes that migrated into the fimbria, corpus callosum, and cerebral cortex. Retroviral injections on P15 labeled very few cells, suggesting depletion of HSVZ progenitors by this age. These findings suggest that the early postnatal HSVZ progenitors are multipotent and migratory, and contribute to both dentate gyrus neurogenesis as well as forebrain gliogenesis.

Isolation of multipotent neural crest-derived stem cells from the adult mouse cornea

We report the presence of neural crest-derived corneal precursors (COPs) that initiate spheres by clonal expansion from a single cell. COPs expressed the stem cell markers nestin, Notch1, Musashi-1, and ABCG2 and showed the side population cell phenotype. COPs were multipotent with the ability to differentiate into adipocytes, chondrocytes, as well as neural cells, as shown by the expression of beta-III-tubulin, glial fibrillary acidic protein, and neurofilament-M. COP spheres prepared from E/nestin-enhanced green fluorescent protein (EGFP) mice showed induction of EGFP expression that was not originally observed in the cornea, indicating activation of the neural-specific nestin second intronic enhancer in culture. COPs were Sca-1(+), CD34(+), CD45(-), and c-kit(-). Numerous GFP(+) cells were observed in the corneas of mice transplanted with whole bone marrow of transgenic mice ubiquitously expressing GFP; however, no GFP(+) COP spheres were initiated from these mice. On the other hand, COP spheres from transgenic mice encoding P0-Cre/Floxed-EGFP as well as Wnt1-Cre/Floxed-EGFP were GFP(+), indicating the neural crest origin of COPs, which was confirmed by the expression of the embryonic neural crest markers Twist, Snail, Slug, and Sox9. Taken together, these data indicate the existence of neural crest-derived, multipotent stem cells in the adult cornea.

Neurogenesis in the adult central nervous system

Contrary to the long-held dogma, neurogenesis occurs throughout adulthood, and neural stem cells reside in the adult central nervous system (CNS) in mammals. The developmental process of the brain may thus never end, and the brain may be amenable to repair. Neurogenesis is modulated in a wide variety of physiological and pathological conditions, and is involved in processes such as learning and memory and depression. However, the relative contribution of newly generated neuronal cells to these processes, as well as to CNS plasticity, remains to be determined. Thus, not only neurogenesis contributes to reshaping the adult brain, it will ultimately lead us to redefine our knowledge and understanding of the nervous system.

Investigation of Musashi-1 expressing cells in the murine model of dextran sodium sulfate-induced colitis

Musashi-1 (Msi-1), an RNA-binding protein, had been proposed to be a specific marker for neural stem/precursor cells. Msi-1 expressing cells in the intestinal epithelium are also strongly considered as potential stem/precursor cells. To clarify the behavior of those cells in the injury or regeneration phase, we investigated Msi-1 expressing cells of intestinal mucosa in the murine model of dextran sodium sulfate (DSS)-induced colitis. Immunohistochemically, Msi-1-positive cells were found in the area just along the layer of Paneth's cells in the small intestine and in the bottom layer of crypts in the large intestine. During DSS administration, the number of PCNA-positive cells in the large intestine increased markedly. In contrast, the number of Msi-1-positive cells decreased slightly with DSS but returned to normal after DSS administration was stopped. The level of mRNA for Msi-1 was consistent with the result of immunohistochemical examinations. Conclusively, we could describe the behavior of intestinal stem/precursor cells during inflammation using Msi-1.

Dynein light chain Tctex-1 identifies neural progenitors in adult brain

The identity and biology of stem cells and progenitors in the adult brain are of considerable interest, because these cells hold great promise for the development of novel therapies for damaged brain tissue in human diseases. This research field critically needs biological markers that specifically identify the resident precursors in the germinal zones of the adult central nervous system so that the discovery of regulatory influences for adult neurogenesis may be facilitated. In this study, by using a combination of in situ hybridization, bromodeoxyuridine incorporation, immunocolocalization, and ultrastructural studies, we show that in rodents Tctex-1, a cytoplasmic dynein light chain, is selectively enriched in almost all cycling progenitors and young neuronal progeny, but not in mature granular cells and astrocytes, in the subgranular zone of the adult dentate gyrus. Tctex-1 is also selectively abundant in cells closely resembling previously described immature progenitors and migrating neuroblasts at the subventricular zone of the lateral ventricle. Our results suggest that Tctex-1 serves as a novel marker for the identification of neural progenitors of the adult brain.

Mesodermal cell types induce neurogenesis from adult human hippocampal progenitor cells

Neurogenesis in the adult human brain occurs within two principle neurogenic regions, the hippocampus and the subventricular zone (SVZ) of the lateral ventricles. Recent reports demonstrated the isolation of human neuroprogenitor cells (NPCs) from these regions, but due to limited tissue availability the knowledge of their phenotype and differentiation behavior is restricted. Here we characterize the phenotype and differentiation capacity of human adult hippocampal NPCs (hNPCs), derived from patients who underwent epilepsy surgery, on various feeder cells including fetal mixed cortical cultures, mouse embryonic fibroblasts (MEFs) and PA6 stromal cells. Isolated hNPCs were cultured in clonal density by transferring the cells to serum-free media supplemented with FGF-2 and EGF in 3% atmospheric oxygen. These hNPCs showed neurosphere formation, expressed high levels of early neuroectodermal markers, such as the proneural genes NeuroD1 and Olig2, the NSC markers Nestin and Musashi1, the proliferation marker Ki67 and significant activity of telomerase. The phenotype was CD15low/-, CD34-, CD45- and CD133-. After removal of mitogens and plating them on poly D-lysine, they spontaneously differentiated into a neuronal (MAP2ab+), astroglial (GFAP+), and oligodendroglial (GalC+) phenotype. Differentiated hNPCs showed functional properties of neurons, such as sodium channels, action potentials and production of the neurotransmitters glutamate and GABA. Co-culture of hNPCs with fetal cortical cultures, MEFs and PA6 cells increased neurogenesis of hNPCs in vitro, while only MEFs and PA6 cells also led to a morphological and functional neurogenic maturation. Together we provide a first detailed characterization of the phenotype and differentiation potential of human adult hNPCs in vitro. Our findings reinforce the emerging view that the differentiation capacity of adult hNPCs is critically influenced by non-neuronal mesodermal feeder cells.

A role for the ELAV RNA-binding proteins in neural stem cells: stabilization of Msi1 mRNA

Post-transcriptional regulation exerted by neural-specific RNA-binding proteins plays a pivotal role in the development and maintenance of the nervous system. Neural ELAV proteins are key inducers of neuronal differentiation through the stabilization and/or translational enhancement of target transcripts bearing the AU-rich elements (AREs), whereas Musashi-1 maintains the stem cell proliferation state by acting as a translational repressor. Since the gene encoding Musashi-1 (Msi1) contains a conserved ARE in its 3' untranslated region, we focused on the possibility of a mechanistic relationship between ELAV proteins and Musashi-1 in cell fate commitment. Colocalization of neural ELAV proteins with Musashi-1 clearly shows that ELAV proteins are expressed at early stages of neural commitment, whereas interaction studies demonstrate that neural ELAV proteins exert an ARE-dependent binding activity on the Msi1 mRNA. This binding activity has functional effects, since the ELAV protein family member HuD is able to stabilize the Msi1 ARE-containing mRNA in a sequence-dependent way in a deadenylation/degradation assay. Furthermore activation of the neural ELAV proteins by phorbol esters in human SH-SY5Y cells is associated with an increase of Musashi-1 protein content in the cytoskeleton. We propose that ELAV RNA-binding proteins exert an important post-transcriptional control on Musashi-1 expression in the transition from proliferation to neural differentiation of stem/progenitor cells.

Comparative analysis of neuroectodermal differentiation capacity of human bone marrow stromal cells using various conversion protocols

Human adult bone marrow-derived mesodermal stromal cells (hMSCs) are able to differentiate into multiple mesodermal tissues, including bone and cartilage. There is evidence that these cells are able to break germ layer commitment and differentiate into cells expressing neuroectodermal properties. There is still debate about whether this results from cell fusion, aberrant marker gene expression or real neuroectodermal differentiation. Here we extend our work on neuroectodermal conversion of adult hMSCs in vitro by evaluating various epigenetic conversion protocols using quantitative RT-PCR and immunocytochemistry. Undifferentiated hMSCs expressed high levels of fibronectin as well as several neuroectodermal genes commonly used to characterize neural cell types, such as nestin, beta-tubulin III, and GFAP, suggesting that hMSCs retain the ability to differentiate into neuroectodermal cell types. Protocols using a direct differentiation of hMSCs into a neural phenotype failed to induce significant changes in morphology and/or expression of markers of early and mature glial/neuronal cells types. In contrast, a multistep protocol with conversion of hMSCs into a neural stem cell-like population and subsequent terminal differentiation in mature glia and neurons generated relevant morphological changes as well as significant increase of expression levels of marker genes for early and late neural cell types, such as nestin, neurogenin2, MBP, and MAP2ab, accompanied by a loss of their mesenchymal properties. Our data provide an impetus for differentiating hMSCs in vitro into mature neuroectodermal cells. Neuroectodermally converted hMSCs may therefore ultimately help in treating acute and chronic neurodegenerative diseases. Analysis of marker gene expression for characterization of neural cells derived from MSCs has to take into account that several early and late neuroectodermal genes are already expressed in undifferentiated MSCs.

EphB Receptors Coordinate Migration and Proliferation in the Intestinal Stem Cell Niche

More than 10(10) cells are generated every day in the human intestine. Wnt proteins are key regulators of proliferation and are known endogenous mitogens for intestinal progenitor cells. The positioning of cells within the stem cell niche in the intestinal epithelium is controlled by B subclass ephrins through their interaction with EphB receptors. We report that EphB receptors, in addition to directing cell migration, regulate proliferation in the intestine. EphB signaling promotes cell-cycle reentry of progenitor cells and accounts for approximately 50% of the mitogenic activity in the adult mouse small intestine and colon. These data establish EphB receptors as key coordinators of migration and proliferation in the intestinal stem cell niche.

The RNA-binding protein Musashi is required intrinsically to maintain stem cell identity

A key goal of regenerative medicine is an understanding of the genetic factors that define the properties of stem cells. However, stem cell research in mammalian tissue has been hampered by a paucity of stem cell-specific markers. Although increasing evidence suggests that members of the Musashi (Msi) family of RNA-binding proteins play important functions in progenitor cells, it remains unclear whether there is a stem cell-autonomous requirement for Msi because of an inability to distinguish stem cells from early-lineage cells in mammalian tissues. Here, using the Drosophila testis as a model system for the study of stem cell regulation, we show specific evidence for a cell-autonomous requirement for Msi family proteins in regulating stem cell differentiation, leading to the identification of an RNA-binding protein required for spermatogonial stem cell maintenance. We found that loss of Msi function disrupts the balance between germ-line stem cell renewal and differentiation, resulting in the premature differentiation of germ-line stem cells. Moreover, we found that, although Msi is expressed in both somatic and germ cells, Msi function is required intrinsically in stem cells for maintenance of stem cell identity. We also discovered a requirement for Msi function in male meiosis, revealing that Msi has distinct roles at different stages of germ cell differentiation. We describe the complementary expression patterns of the murine Msi paralogues Msi1 and Msi2 during spermatogenesis, which support the idea of distinct, evolutionarily conserved roles of Msi.

Neurogenic potential of human umbilical cord blood: neural-like stem cells depend on previous long-term culture conditions

In vitro studies conducted by our research group documented that neural progenitor cells can be selected from human umbilical cord blood (HUCB-NPs). Due to further expansion of these cells we have established the first human umbilical cord blood-derived neural-like stem cell line (HUCB-NSC) growing in serum-free (SF) or low-serum (LS) medium for over 3 years. The purpose of the study was to evaluate the neurogenic potential of HUCB-NSCs cultured in SF and LS condition in different in vitro settings before transplantation. We have shown that the number of cells attaining neuronal features was significantly higher for cultures expanded in LS than in SF condition. Moreover, the presence of neuromorphogens, cultured rat astrocytes or hippocampal slices promoted further differentiation of HUCB-NSCs into neural lineage much more effectively when the cells had derived from LS cultures. The highest response was observed in the case of co-cultures with rat primary astrocytes as well as hippocampal organotypic slices. However, the LS cells co-cultured with hippocampal slices expressed exclusively a set of early and late neuronal markers whereas no detection of cells with glial-specific markers was possible. In conclusion, certain level of stem/progenitor cell commitment is important for optimal response of HUCB-NSC on the neurogenic signals provided by surrounding environment in vitro.

HPSE-1 expression and functionality in differentiating neural cells

The study of cellular differentiation encompasses many vital parts of biology and medicine. Heparan sulfate proteoglycans (HSPG) are essential and ubiquitous macromolecules associated with the cell surface and extracellular matrix (ECM) of a wide range of cells and tissues. Heparan sulfate chains (HS) of HSPG bind and sequester a multitude of extracellular ligands, including growth factors, cytokines, chemokines, enzymes, and lipoproteins. Enzymatic degradation of HS is therefore involved in processes such as cell proliferation, migration, and differentiation. Heparanase (HPSE-1) is an HS degradative enzyme associated with inflammation and lipid metabolism and is a critical molecular determinant in cancer metastasis. The enzyme acts as an endo-beta-D-glucuronidase, which degrades HS at specific intrachain sites, resulting in HS fragments of discrete molecular weights that retain biological function. HPSE-1's relevance as the only example of cloned/purified mammalian HS degradative enzyme led us to investigate its functionality in human olfactory epithelium (HOE) cells as a paradigm for HPSE-1's roles in neural cell differentiation. We provide the first evidence of 1) HPSE-1 presence in HOE cells and 2) a highly significant increase of HPSE-1 mRNA and enzyme activity in differentiating vs. proliferating HOE cells. Our data suggest that an augmented HPSE-1 activity may represent a physiological mechanism involved in neural cellular differentiation.

Enhanced therapeutic efficacy of G207 for the treatment of glioma through Musashi1 promoter retargeting of gamma34.5-mediated virulence

G207 is a conditionally replicating derivative of herpes simplex virus type1 (HSV-1) engineered with deletions of both ICP34.5 loci and a lacZ insertion disabling the ICP6 gene. G207 exhibits an efficient oncolytic activity in vitro and in vivo, yet minimal toxicity in normal tissue, and is now in clinical trial for malignant glioma. According to the results of clinical trials, however, although G207 was proved to be safe, the efficacy was not so impressive. Deletion of the ICP34.5 gene coding for virulence made G207 extremely safe, but it markedly reduced the cytotoxicity mediated by HSV-1. To enhance the therapeutic efficacy of G207 without diminishing its safety, we used a defective vector containing Musashi1 promoter/ICP34.5, with G207 as helper virus. P/musashi1 was functional selectively in human glioma cell lines (U87MG, U251, T98G) in this study and dvM345 showed a much higher therapeutic efficacy both in culture and in the in vivo glioma model, than G207 alone, without diminishing its favorable toxicity profile. These results suggest that transcriptional regulation of ICP34.5 by P/musashi1 can be used to target HSV-1 virulence toward gliomas while maintaining the desirable neuroattenuated phenotype.

Peroxisome Proliferator-activated Receptor γ-mediated Regulation of Neural Stem Cell Proliferation and Differentiation

Peroxisome proliferator-activated receptor gamma (PPARgamma) plays an important role in insulin sensitivity, tissue homeostasis, and regulating cellular functions. We found high-level expression of PPARgamma in embryo mouse brain and neural stem cells (NSCs), in contrast to extremely low levels in adult mouse brain. Here, we show that PPARgamma mediates the proliferation and differentiation of murine NSCs via up-regulation of the epidermal growth factor receptor and activation of the ERK pathway. Cell growth rates of NSCs prepared from heterozygous PPARgamma-deficient mouse brains, PPARgamma-RNA-silenced NSCs, and PPARgamma dominant-negative NSCs were significantly decreased compared with those of wild-type NSCs. Physiological concentrations of PPARgamma agonists, rosiglitazone and pioglitazone, stimulated NSC growth, whereas antagonists caused cell death in a concentration-dependent manner via activation of the caspase cascade. The stimulation of cell growth by PPARgamma was associated with a rapid activation of the ERK pathway by phosphorylation and up-regulation of epidermal growth factor receptor and cyclin B protein levels. In contrast, activation of PPARgamma by agonists inhibited the differentiation of NSCs into neurons. The inhibition of differentiation was associated with an activation of STAT3. These data indicate that PPARgamma regulates the development of the central nervous system during early embryogenesis via control of NSC proliferation.

The endocannabinoid system promotes astroglial differentiation by acting on neural progenitor cells

Endocannabinoids exert an important neuromodulatory role via presynaptic cannabinoid CB1 receptors and may also participate in the control of neural cell death and survival. The function of the endocannabinoid system has been extensively studied in differentiated neurons, but its potential role in neural progenitor cells remains to be elucidated. Here we show that the CB1 receptor and the endocannabinoid-inactivating enzyme fatty acid amide hydrolase are expressed, both in vitro and in vivo, in postnatal radial glia (RC2+ cells) and in adult nestin type I (nestin(+)GFAP+) neural progenitor cells. Cell culture experiments show that CB1 receptor activation increases progenitor proliferation and differentiation into astroglial cells in vitro. In vivo analysis evidences that, in postnatal CB1(-/-) mouse brain, progenitor proliferation and astrogliogenesis are impaired. Likewise, in adult CB1-deficient mice, neural progenitor proliferation is decreased but is increased in fatty acid amide hydrolase-deficient mice. In addition, endocannabinoid signaling controls neural progenitor differentiation in the adult brain by promoting astroglial differentiation of newly born cells. These results show a novel physiological role of endocannabinoids, which constitute a new family of signaling cues involved in the regulation of neural progenitor cell function.

Expression of RNA-binding protein Musashi in hair follicle development and hair cycle progression

Epithelial stem cells reside in the hair follicle (HF) bulge region and possess the ability to differentiate into a variety of cutaneous epithelial cells. The evolutionarily conserved Musashi family of RNA-binding proteins is associated with maintenance and/or asymmetric cell division of neural progenitor cells, and a mammalian Musashi protein is expressed in various epithelial stem/progenitor cells, including gut, stomach, and mammary gland. Thus, we hypothesized that Musashi might be expressed in stem cells and early progenitor cells of HF epithelium. Reverse transcriptase-polymerase chain reaction and immunoblotting identified Musashi-1 (Msi-1) and Musashi-2 (Msi-2) mRNA and protein in cultured mouse keratinocytes, but only Msi-1 was identified in human keratinocytes. In mice, immunohistochemical studies showed that Msi-1 and Msi-2 were expressed in the epidermis and HFs from E14.5 until adulthood. In the early anagen phase, Msi-1 and Msi-2 were expressed in the bulge and secondary germ cells and subsequently in inner root sheath (IRS) cells, especially the middle IRS cells, during the late anagen phase. In human skin, Msi-1 was detected in fetal HF cells but not in adult HFs. These observations suggest that Musashi functions not only in the asymmetric division of early progenitor cells but also in the differentiation of IRS cells during HF development and hair cycle progression.

CCAAT/enhancer-binding protein phosphorylation biases cortical precursors to generate neurons rather than astrocytes in vivo

The intracellular mechanisms that bias mammalian neural precursors to generate neurons versus glial cells are not well understood. We demonstrated previously that the growth factor-regulated mitogen-activated protein kinase kinase (MEK) and its downstream target, the CCAAT/enhancer-binding protein (C/EBP) family of transcription factors, are essential for neurogenesis in cultured cortical precursor cells (Ménard et al., 2002). Here, we examined a role for this pathway during cortical cell fate determination in vivo using in utero electroporation of the embryonic cortex. These studies demonstrate that inhibition of the activity of either MEK or the C/EBPs inhibits the genesis of neurons in vivo. Moreover, the MEK pathway mediates phosphorylation of C/EBPbeta in cortical precursors, and expression of a C/EBPbeta construct in which the MEK pathway phosphorylation sites are mutated inhibits neurogenesis. Conversely, expression of a C/EBPbeta construct, in which the same sites are mutated to glutamate and therefore are "constitutively" phosphorylated, enhances neurogenesis in the early embryonic cortex. A subpopulation of precursors in which C/EBP activity is inhibited are maintained as cycling precursors in the ventricular/subventricular zone of the cortex until early in postnatal life, when they have an enhanced propensity to generate astrocytes, presumably in response to gliogenic signals in the neonatal environment. Thus, activation of an MEK-C/EBP pathway in cortical precursors in vivo biases them to become neurons and against becoming astrocytes, thereby acting as a growth factor-regulated switch.

Administration of hematopoietic cytokines in the subacute phase after cerebral infarction is effective for functional recovery facilitating proliferation of intrinsic neural stem/progenitor cells and transition of bone marrow-derived neuronal cells

BACKGROUND

Hematopoietic cytokines, granulocyte colony-stimulating factor (G-CSF), and stem cell factor (SCF) were reported to show a neuroprotective effect or to support neurogenesis. These cytokines also mobilize bone marrow (BM) cells into the brain, and the BM-derived cells differentiate into neuronal cells. We administered these hematopoietic cytokines after focal cerebral ischemia and assessed their effects and the therapeutic time window for neuronal regeneration.

METHODS AND RESULTS

We induced permanent middle cerebral artery occlusion in mice whose BM had been replaced with BM cells from green fluorescent protein (GFP)-transgenic mice. The occluded mice were treated with G-CSF and SCF in the acute phase (days 1 to 10) or subacute phase (days 11 to 20), and the brain functions and histological changes were evaluated. Separately, we injected bromodeoxyuridine during cytokine treatment to assess cell kinetics in the brain. Six mice were prepared for each experimental group. Administration of G-CSF and SCF in the subacute phase effectively improved not only motor performance but also higher brain function, compared with acute-phase treatment. Acute-phase and subacute-phase treatments identically reduced the infarct volume relative to vehicle treatment. However, subacute-phase treatment significantly induced transition of BM-derived neuronal cells into the peri-infarct area and stimulated proliferation of intrinsic neural stem/progenitor cells in the neuroproliferative zone.

CONCLUSIONS

Administration of G-CSF and SCF in the subacute phase after focal cerebral ischemia is effective for functional recovery, enhancing cytokine-induced generation of neuronal cells from both BM-derived cells and intrinsic neural stem/progenitor cells. Because G-CSF and SCF are available for clinical use, these findings suggest a new therapeutic strategy for stroke.

Combinatorial profiles of oligodendrocyte-selective classes of transcriptional regulators differentially modulate myelin basic protein gene expression

Recent studies suggest that specific neural basic helix-loop-helix (HLH; i.e., Olig1 and Olig2, Mash1), associated inhibitory HLH (i.e., Id2 and Id4), high-mobility group domain (i.e., Sox10), and homeodomain (i.e., Nkx2.2) transcription factors are involved in oligodendrocyte (OL) lineage specification and progressive stages of maturation including myelination. However, the developmental interplay among these lineage-selective determinants, in a cell- and maturational stage-specific context, has not yet been defined. We show here in vivo and in vitro developmental expression profiles for these distinct classes of transcriptional regulators of OLs. We show that progressive stages of OL lineage maturation are characterized by dynamic changes in the subcellular distribution of these transcription factors and by different permutations of combinatorial transcriptional codes. Transient transfections of these precise combinatorial codes with a luciferase reporter gene driven by the myelin basic protein promoter define how changes in the molecular composition of these transcriptional complexes modulate myelin gene expression. Our overall findings suggest that the dynamic interplay between developmental stage-specific classes of transcriptional activators and associated inhibitory factors orchestrate myelin gene expression during terminal maturation of the mammalian CNS.

Development and differentiation of neural rosettes derived from human embryonic stem cells

Neurons and glia are important targets of human embryonic stem cell research, promising a renewable source of these differentiated cells for biomedical research and regenerative medicine. Neurons and glia are derived in vivo from the neuroepithelium of the neural tube. Concomitant to development along the anterior to posterior axis, gradients of morphogens across the dorsal and ventral axis of the neural tube establish positional codes that generate distinct progenitor domains and ultimately specify subtype identity. The neural rosette is the developmental signature of neuroprogenitors in cultures of differentiating embryonic stem cells; rosettes are radial arrangements of columnar cells that express many of the proteins expressed in neuroepithelial cells in the neural tube. In addition to similar morphology, neuroprogenitors within neural rosettes differentiate into the main classes of progeny of neuroepithelial cells in vivo: neurons, oligodendrocytes, and astrocytes. Despite these similarities, important differences exist and the extent to which neural rosettes can model neurogenesis in vivo is not yet clear. Here, the authors review the recent studies on the development and differentiation of neural rosettes from human embryonic stem cells. The authors focus on efforts to generate motor neurons and oligodendrocytes in vitro as representative of the challenges to obtaining the progeny of a single progenitor domain with in vitro methods. Opportunities for further progress are discussed.

Differential neurogenic potential of progenitor cells in dentate gyrus and CA1 sector of the postischemic adult monkey hippocampus

The adult mammalian hippocampus contains neural progenitor cells capable of neuronal production under normal conditions. Cerebral injuries such as ischemia lead to their upregulation in rodent models, resulting in neurogenesis in the dentate gyrus (DG) and CA1 sector. The adult primate DG also has neurogenic potential under normal conditions, and we have previously shown that transient global cerebral ischemia increases progenitor cell proliferation in monkey DG, with a peak in the second postischemic week. Until now, however, long-term effects of ischemia on adult-generated cells in the primate hippocampus have not been described. We show here that nearly 15% of the adult-generated cells in monkey DG express neuronal features in the dentate granule layer for at least 79 days after the insult. At the same time, most adult-born cells in DG sustained their localization in the subgranular zone with an immature progenitor phenotype. In contrast to DG, no signs of neuronal production were observed in the postischemic hippocampus proper and in particular in the CA1 sector, where the newly-born cells were consistently of glial phenotype. Proliferating progenitors in DG but not in the subventricular zone adjacent to CA1 expressed the pro-neural transcription factors Emx2, Pax6 and Ngn2. Taken together, these results suggest that the neuronal production in adult monkey hippocampus after global brain ischemia is limited to DG and does not occur in the hippocampus proper. The present data implicate the proteins Emx2, Pax6 and Ngn2 as putative molecular signals controlling the fate of progenitor cells of the adult primate hippocampus.

Cancer stem cells in the mammalian central nervous system

Malignant tumours intrinsic to the central nervous system (CNS) are among the most difficult of neoplasms to treat effectively. The major biological features of these tumours that preclude successful therapy include their cellular heterogeneity, which renders them highly resistant to both chemotherapy and radiotherapy, and the propensity of the component tumour cells to invade, diffusely, the contiguous nervous tissues. The tumours are classified according to perceived cell of origin, gliomas being the most common generic group. In the 1970s transplacental administration of the potent neurocarcinogen, N-ethyl-N-nitrosourea (ENU), enabled investigation of the sequential development of brain and spinal neoplasms by electron microscopy and immunohistochemistry. The significance of the primitive cells of the subependymal plate in cellular origin and evolution of a variety of glial tumours was thereby established. Since then, the development of new cell culture methods, including the in vitro growth of neurospheres and multicellular tumour spheroids, and new antigenic markers of stem cells and glial/neuronal cell precursor cells, including nestin, Mushashi-1 and CD133, have led to a reappraisal of the histological classification and origins of CNS tumours. Moreover, neural stem cells may also provide new vectors in exciting novel therapeutic strategies for these tumours. In addition to the gliomas, stem cells may have been identified in paediatric tumours including cerebellar medulloblastoma, thought to be of external granule cell neuronal derivation. Interestingly, while the stem cell marker CD133 is expressed in these primitive neuroectodermal tumours (PNETs), the chondroitin sulphate proteoglycan neuronal/glial 2 (NG2), which appears to denote increased proliferative, but reduced migratory activity in adult gliomas, is rarely expressed. This is in contrast to the situation in the histologically similar supratentorial PNETs. A possible functional 'switch' between proliferation and migration in developing neural tumour cells may exist between NG2 and ganglioside GD3. The divergent pathways of differentiation of CNS tumours and the possibility of stem cell origin, for some, if not all, such neoplasms remain a matter for debate and continued research, but the presence of self-renewing neural stem cells in the CNS of both children and adults strongly suggests a role for these cells in tumour initiation and resistance to current therapeutic strategies.

Pax6 is required for production and maintenance of progenitor cells in postnatal hippocampal neurogenesis

Neurogenesis is crucial for brain formation and continues to take place in certain regions of the postnatal brain including the subgranular zone (SGZ) of the hippocampal dentate gyrus (DG). Pax6 transcription factor is a key player for patterning the brain and promoting embryonic neurogenesis, and is also expressed in the SGZ. In the DG of wild-type rats, more than 90% of total BrdU-incorporated cells expressed Pax6 at 30 min time point after BrdU injection. Moreover, approximately 60% of Pax6+ cells in the SGZ exhibited as GFAP+ cells with a radial glial phenotype and about 30% of Pax6+ cells exhibited as PSA-NCAM+ cells in clusters. From BrdU labeling for 3 days, we found that cell proliferation was 30% decreased at postnatal stages in Pax6-deficient rSey2/+ rat. BrdU pulse/chase experiments combined with marker staining revealed that PSA-NCAM+ late progenitor cells increased at the expense of GFAP+ early progenitors in rSey2/+ rat. Furthermore, expression of Wnt ligands in the SGZ was markedly reduced in rSey2/+ rat. Taken all together, an appropriate dosage of Pax6 is essential for production and maintenance of the GFAP+ early progenitor cells in the postnatal hippocampal neurogenesis.

Neoplastic stem cells: A novel therapeutic target in clinical oncology

Cancer is among the leading causes of morbidity and mortality in the Western world. Despite recent advances, most therapeutic approaches fail to eradicate the entire neoplastic clone. The remaining cells often develop metastasis and/or recurrences and therefore may represent attractive targets of therapy. A new exciting concept in this regard suggests that each neoplasm represents a heterogeneous population of cells that pertain to long-term tumor growth both in vivo in the natural host and in experimental animals. This concept postulates the existence of small fractions of 'tumor stem cells' that exhibit a capacity for self-renewal and unlimited growth and therefore are distinct from their progeny. Based on these hypotheses, the targeting of neoplastic stem cells is considered indispensable for eradication of the entire clone and for the development of curative treatment approaches. However, tumor stem cells often may be quiescent cells and may express a different profile of targets compared with 'more mature' tumor cells. Therefore, current efforts have attempted to characterize target expression profiles in cancer stem cells in various malignancies. In the this review, the authors have provided a brief summary of the current knowledge of neoplastic stem cells and the application of respective concepts in translational oncology with the ultimate objective of improving anticancer therapy.

Survival of neural precursor cells in growth factor-poor environment: Implications for transplantation in chronic disease

A key issue for therapeutic neural stem cell transplantation in chronic diseases is the long-term survival of transplanted cells in the brain. The normal adult central nervous system does not support the survival of transplanted cells. Presumably, the limited availability of trophic factors maintains the survival of resident cells but is insufficient for supporting the survival of transplanted cells. Specifically, in multiple sclerosis, a chronic relapsing disease, it would be necessary to maintain long-term survival of transplanted cells through phases of relapses and remissions. It may be beneficial to transplant cells as early as possible, in a form that will keep their survival independent of tissue support and ready for immediate mobilization upon tissue demand during disease relapse. In the present study, we examined whether, in the form of neurospheres, multipotential neural precursor cells (NPCs) survive in a growth factor-poor environment while maintaining their potential to respond to environmental cues. We found that after removal of growth factors from the culture medium of neurospheres in vitro, NPC proliferation decreased significantly, but most cells survived for a prolonged time and maintained their stem cell characteristics. After re-exposure to growth factors, neurosphere cells resumed proliferation and could differentiate along neural lineages. Furthermore, neurospheres, but not single NPCs, that were transplanted into the brain ventricles of intact animals survived within the ventricles for at least a month and responded to induction of experimental autoimmune encephalomyelitis and brain inflammation by extensive migration into the brain white matter and differentiated into glial lineage cells.

Transcription factor protein expression patterns by neural or neuronal progenitor cells of adult monkey subventricular zone

The anterior subventricular zone of the adult mammalian brain contains progenitor cells which are upregulated after cerebral ischemia. We have previously reported that while a part of the progenitors residing in adult monkey anterior subventricular zone travels to the olfactory bulb, many of these cells sustain location in the anterior subventricular zone for months after injury, exhibiting a phenotype of either neural or neuronal precursors. Here we show that ischemia increased the numbers of anterior subventricular zone progenitor cells expressing developmentally regulated transcription factors including Pax6 (paired-box 6), Emx2 (empty spiracles-homeobox 2), Sox 1-3 (sex determining region Y-box 1-3), Ngn1 (neurogenin 1), Dlx1,5 (distalless-homeobox 1,5), Olig1,3 (oligodendrocyte lineage gene 1,3) and Nkx2.2 (Nk-box 2.2), as compared with control brains. Analysis of transcription factor protein expression by sustained neural or neuronal precursors in anterior subventricular zone revealed that these two cell types were positive for characteristic sets of transcription factors. The proteins Pax6, Emx2, Sox2,3 and Olig1 were predominantly localized to dividing neural precursors while the factors Sox1, Ngn1, Dlx1,5, Olig2 and Nkx2.2 were mainly expressed by neuronal precursors. Further, differences between monkeys and non-primate mammals emerged, related to expression patterns of Pax6, Olig2 and Dlx2. Our results suggest that a complex network of developmental signals might be involved in the specification of primate progenitor cells.

The RNA-binding protein Musashi-1 regulates neural development through the translational repression of p21WAF-1

RNA-binding proteins regulate cell fate decisions during nervous system development. The Msi family of RNA-binding proteins is expressed in multipotential neural progenitors, and is required for maintaining cells in a proliferative state. We demonstrate that Msi-1's ability to regulate progenitor maintenance is through the translational inhibition of the cyclin-dependent kinase inhibitor p21WAF-1. Msi-1 ectopic expression increases the proliferation rate and the capacity to regulate p21WAF-1 protein expression, independent of p53. The 3' untranslated region (UTR) of the native p21(WAF-1) mRNA contains a Msi-1 consensus-binding site that permits Msi-1 to directly repress the translation of p21WAF-1 protein. Reduction of Msi-1 through antisense leads to aberrant p21WAF-1 expression, which significantly impairs neural differentiation. A double knockdown for p21WAF-1 and Msi-1 rescues the production of mature MAP+ neurons. Our results further elucidate the symbiotic relationship between cell cycle withdrawal and the onset of differentiation in the developing nervous system, as well as increasing the understanding of the influence that RNA-binding proteins serve in regulating these processes.

The gastrointestinal tract stem cell niche

The gastrointestinal epithelium is unique in that cell proliferation, differentiation, and apoptosis occur in an orderly fashion along the crypt-villus axis. The intestinal crypt is mainly a proliferative compartment, is monoclonal and is maintained by stem cells. The villus represents the differentiated compartment, and is polyclonal as it receives cells from multiple crypts. In the small intestine, cell migration begins near the base of the crypt, and cells migrate from here emerging onto the villi. The basal crypt cells at position 5 are candidate stem cells. As the function of stem cells is to maintain the integrity of the intestinal epithelium, it must self-renew, proliferate, and differentiate within a protective niche. This niche is made up of proliferating and differentiating epithelial cells and surrounding mesenchymal cells. These mesenchymal cells promote the epithelial- mesenchymal crosstalk required to maintain the niche. A stochastic model of cell division has been proposed to explain how a single common ancestral stem cell exists from which all stem cells in a niche are descended. Our group has argued that these crypts then clonally expand by crypt fission, forming two daughters' crypts, and that this is the mechanism by which mutated stem cells or even cancer stem cell clones expand in the colon and in the entire gastrointestinal tract. Until recently, the differentiation potential of stem cells into adult tissues has been thought to be limited to cell lineages in the organ from which they were derived. Bone marrow cells are rare among adult stem cells regarding their abundance and role in the continuous, lifelong, physiological replenishment of circulating cells. In human and mice experiments, we have shown that bone marrow can contribute to the regeneration of intestinal myofibroblasts and thereby after epithelium following damage, through replacing the cells, which maintain the stem cells niche. Little is known about the markers characterizing the stem and transit amplifying populations of the gastrointestinal tract, although musashi-1 and hairy and enhancer of split homolog-1 have been proposed. As the mammalian gastrointestinal tract develops from the embryonic gut, it is made up of an endodermally-derived epithelium surrounded by cells of mesoderm origin. Cell signaling between these two tissue layers plays a critical role in coordinating patterning and organogenesis of the gut and its derivatives. Many lines of evidence have revealed that Wnt signaling is the most dominant force in controlling cell proliferation, differentiation, and apoptosis along the crypt-villus axis. We have found Wnt messenger RNAs expression in intestinal subepithelial myofibroblasts and frizzled messenger RNAs expression in both myofibroblasts and crypt epithelium. Moreover, there are many other factors, for example, bone morphogenetic protein, homeobox, forkhead, hedgehog, homeodomain, and platelet-derived growth factor that are also important to stem cell signaling in the gastrointestinal tract.

Biological Principles for Ex Vivo Adult Stem Cell Expansion

Adult stem cells (ASCs) are the engines that drive the renewal of adult mammalian tissues. They divide continuously, throughout life, to produce new progeny cells that undergo a robust development program of differentiation and maturation to replace older expired tissue cells. The same cell turnover program may function to provide limited repair and regeneration of adult tissues in some cases. The regenerative potential of ASCs drives the current intense interest in adapting them for applications in cell replacement therapy. However, research to explore this potential has been blunted by an unyielding biological problem. ASCs have proven highly refractory to expansion of their numbers and long-term propagation in culture. A review of reported strategies to overcome this problem reveals that many studies focus on traditional cell culture factors that may not apply to ASCs and overlook a special property of ASCs that may be universally critical for successful expansion, asymmetric cell kinetics (ACK). This property is reflected by the different kinetics fate of the two sister cells resulting from an ASC division: one cell remains an ASC and keeps the potential to divide for the entire life span of the tissue, while the other cell's progeny eventually differentiates and undergoes terminal division arrest. This unique property of ASCs may prove to be the obligatory factor that must be breached by any method that will succeed in accomplishing routine expansion of ASCs of diverse tissue origin.

Adult neural stem cells and central nervous system repair

It has long been believed that the adult mammalian central nervous system does not regenerate after injury. However, recent advances in the field of stem cell biology, including the identification of Musashi-1-positive neural stem cells (NSCs) or NSC-like cells, has provided new insight for the development of novel therapeutic strategies aimed at inducing regeneration in the damaged central nervous system (CNS). The major strategies for inducing regeneration in the damaged CNS can be classified into two subgroups: (1) activation of endogenous neural stem cells and (2) cell transplantation therapies. In this paper, we would like to summarize our recent findings on the functions of the neural RNA-binding protein Musashi-l expressed in neural stem cells in relation to insult-induced neurogenesis, and therapeutic interventions for spinal cord injury, especially focusing on the treatment of spinal cord injury in the acute phase with anti-IL-6 receptor blocking antibody.

Multipotent neural stem cells from the adult tegmentum with dopaminergic potential develop essential properties of functional neurons

Neurogenesis in the adult brain occurs within the two principal neurogenic regions: the hippocampus and the subventricular zone of the lateral ventricles. The occurrence of adult neurogenesis in non-neurogenic regions, including the midbrain, remains controversial, but isolation of neural stem cells (NSCs) from several parts of the adult brain, including the substantia nigra, has been reported. Nevertheless, it is unclear whether adult NSCs do have the capacity to produce functional dopaminergic neurons, the cell type lost in Parkinson's disease. Here, we describe the isolation, expansion, and in vitro characterization of adult mouse tegmental NSCs (tNSCs) and their differentiation into functional nerve cells, including dopaminergic neurons. These tNSCs showed neurosphere formation and expressed high levels of early neuroectodermal markers, such as the proneural genes NeuroD1, Neurog2, and Olig2, the NSC markers Nestin and Musashi1, and the proliferation markers Ki67 and BrdU (5-bromo-2-deoxyuridine). The cells showed typical propidium iodide-fluorescence-activated cell sorting analysis of slowly dividing cells. In the presence of selected growth factors, tNSCs differentiated into astroglia, oligodendroglia, and neurons expressing markers for cholinergic, GABAergic, and glutamatergic cells. Electrophysiological analyses revealed functional properties of mature nerve cells, such as tetrodotoxin-sensitive sodium channels, action potentials, as well as currents induced by GABA (gamma-aminobutyric acid), glutamate, and NMDA (N-methyl-D-aspartate). Clonal analysis demonstrated that individual NSCs retain the capacity to generate both glia and neurons. After a multistep differentiation protocol using co-culture conditions with PA6 stromal cells, a small number of cells acquired morphological and functional properties of dopaminergic neurons in culture. Here, we demonstrate the existence of adult tNSCs with functional neurogenic and dopaminergic potential, a prerequisite for future endogenous cell replacement strategies in Parkinson's disease.

Expression of Musashi-1 in the rat stomach and changes during mucosal injury and restitution

Musashi-1 is involved in maintenance of neural stem cells. In the rat stomach, we found some cells in the luminal compartment of the mucosa that stained positively for Musashi-1. These cells were distinct from other cells of epithelial lineage, except for parietal cells, and coexpressed HES5. The Musashi-1-positive cells exfoliated after damage, while Musashi-1 expression in neck cells were upregulated, and proliferating cells diminished before reappearing and increasing in number thereafter. We conclude that a subpopulation of parietal cells acts as a source of Musashi-1, which contributes to rapid re-epithelization by restoration of stem cells and regulation of cell differentiation.

Brg1 is required for murine neural stem cell maintenance and gliogenesis

Epigenetic alterations in cell-type-specific gene expression control the transition of neural stem cells (NSCs) from predominantly neurogenic to predominantly gliogenic phases of differentiation, but how this switch occurs is unclear. Here, we show that brahma-related gene 1 (Brg1), an ATP-dependent chromatin remodeling factor, is required for the repression of neuronal commitment and the maintenance of NSCs in a state that permits them to respond to gliogenic signals. Loss of Brg1 in NSCs in conditional brg1 mutant mice results in precocious neuronal differentiation, such that cells in the ventricular zone differentiate into post-mitotic neurons before the onset of gliogenesis. As a result, there is a dramatic failure of astrocyte and oligodendrocyte differentiation in these animals. The ablation of brg1 in gliogenic progenitors in vitro also prevents growth-factor-induced astrocyte differentiation. Furthermore, proteins implicated in the maintenance of stem cells, including Sox1, Pax6 and Musashi-1, are dramatically reduced in the ventricular zones of brg1 mutant mice. We conclude that Brg1 is required to repress neuronal differentiation in NSCs as a means of permitting glial cell differentiation in response to gliogenic signals, suggesting that Brg1 regulates the switch from neurogenesis to gliogenesis.