Marrow-mindedness: a perspective on neuropoiesis

Out of Line or Altered States? Neural Progenitors as a Target in a Polygenic Neurodevelopmental Disorder

The genesis of a mature complement of neurons is thought to require, at least in part, precursor cell lineages in which neural progenitors have distinct identities recognized by exclusive expression of one or a few molecular markers. Nevertheless, limited progenitor types distinguished by specific markers and lineal progression through such subclasses cannot easily yield the magnitude of neuronal diversity in most regions of the nervous system. The late Verne Caviness, to whom this edition of Developmental Neuroscience is dedicated, recognized this mismatch. In his pioneering work on the histogenesis of the cerebral cortex, he acknowledged the additional flexibility required to generate multiple classes of cortical projection and interneurons. This flexibility may be accomplished by establishing cell states in which levels rather than binary expression or repression of individual genes vary across each progenitor's shared transcriptome. Such states may reflect local, stochastic signaling via soluble factors or coincidence of cell surface ligand/receptor pairs in subsets of neighboring progenitors. This probabilistic, rather than determined, signaling could modify transcription levels via multiple pathways within an apparently uniform population of progenitors. Progenitor states, therefore, rather than lineal relationships between types may underlie the generation of neuronal diversity in most regions of the nervous system. Moreover, mechanisms that influence variation required for flexible progenitor states may be targets for pathological changes in a broad range of neurodevelopmental disorders, especially those with polygenic origins.

Stem Cells and Regeneration in the Retina: What Fish Have Taught Us about Neurogenesis

Many species of fish grow for much of their lifetimes and add neurons to the CNS continuously. The retina has proved to be a convenient model in which to study neurogenesis, both the normal variety associated with growth and regeneration in response to a lesion. Initial neurogenesis in the embryonic eye cup begins in a tiny cluster of neuroepithelial cells that steadily enlarges to produce a central disk of neurons. Subsequent growth occurs mainly at the edge of this disk, in the circumferential germinal zone, where the retina adds annuli of new neurons of all varieties except the rod photoreceptors. A few proliferative cells persist to adulthood in central retina and normally produce only rods, but when the retina is damaged, these cells contribute to the production of new neurons of diverse classes. Recent work has revealed two additional populations of dividing cells in central retina; they normally proliferate so slowly that special methods are required to reveal them. We suggest that the three proliferative cell types are related through lineage in a model similar to those described for hematopoiesis. The persistent neurogenesis of fish retina seems to resemble qualitatively the neurogenesis of the mammalian brain, but quantitatively the neurogenesis is much more vigorous in the fish.

Migration of bone marrow progenitor cells in the adult brain of rats and rabbits

Neurogenesis takes place in the adult mammalian brain in three areas: Subgranular zone of the dentate gyrus (DG); subventricular zone of the lateral ventricle; olfactory bulb. Different molecular markers can be used to characterize the cells involved in adult neurogenesis. It has been recently suggested that a population of bone marrow (BM) progenitor cells may migrate to the brain and differentiate into neuronal lineage. To explore this hypothesis, we injected recombinant SV40-derived vectors into the BM and followed the potential migration of the transduced cells. Long-term BM-directed gene transfer using recombinant SV40-derived vectors leads to expression of the genes delivered to the BM firstly in circulating cells, then after several months in mature neurons and microglial cells, and thus without central nervous system (CNS) lesion. Most of transgene-expressing cells expressed NeuN, a marker of mature neurons. Thus, BM-derived cells may function as progenitors of CNS cells in adult animals. The mechanism by which the cells from the BM come to be neurons remains to be determined. Although the observed gradual increase in transgene-expressing neurons over 16 mo suggests that the pathway involved differentiation of BM-resident cells into neurons, cell fusion as the principal route cannot be totally ruled out. Additional studies using similar viral vectors showed that BM-derived progenitor cells migrating in the CNS express markers of neuronal precursors or immature neurons. Transgene-positive cells were found in the subgranular zone of the DG of the hippocampus 16 mo after intramarrow injection of the vector. In addition to cells expressing markers of mature neurons, transgene-positive cells were also positive for nestin and doublecortin, molecules expressed by developing neuronal cells. These cells were actively proliferating, as shown by short term BrdU incorporation studies. Inducing seizures by using kainic acid increased the number of BM progenitor cells transduced by SV40 vectors migrating to the hippocampus, and these cells were seen at earlier time points in the DG. We show that the cell membrane chemokine receptor, CCR5, and its ligands, enhance CNS inflammation and seizure activity in a model of neuronal excitotoxicity. SV40-based gene delivery of RNAi targeting CCR5 to the BM results in downregulating CCR5 in circulating cells, suggesting that CCR5 plays an important role in regulating traffic of BM-derived cells into the CNS, both in the basal state and in response to injury. Furthermore, reduction in CCR5 expression in circulating cells provides profound neuroprotection from excitotoxic neuronal injury, reduces neuroinflammation, and increases neuronal regeneration following this type of insult. These results suggest that BM-derived, transgene-expressing, cells can migrate to the brain and that they become neurons, at least in part, by differentiating into neuron precursors and subsequently developing into mature neurons.

Neurogenic astrocytes and their glycoconjugates: not just "glue" anymore

Cells with certain attributes of very immature astroglial cells and their radial precursors can act as stem and/or progenitor cells during developmental and persistent neurogenesis. Neural stem/progenitor cells both express and are affected by a variety of developmentally regulated macromolecules and growth factors, and such signaling or recognition molecules are being uncovered through extensive genomic and proteomic studies, as well as tested using in vitro/in vivo cell growth bioassays. Glycosylated molecules are appreciated as distinct signaling molecules during morphogenesis in a variety of tissues and organs, with glycoconjugates (glycoproteins, glycolipids, and glycosaminoglycans) serving as mediators for the interactions of cells with each other and their substrates, to confer growth and differentiation cues to precursor cells in search of identity. Neurogenic astrocytes and associated glycoconjugates, especially extracellular matrix molecules, are discussed in the context of neurogenesis and stem/progenitor cell growth, fate choice, and differentiation.

Stem cells in the treatment of stroke

Stroke is an often devastating insult resulting in neurological deficit lasting greater than 24 hours. In the United States, stroke is the third leading cause of death. In those who do not succumb, any outcome from total recovery over a period of weeks to months to persistent profound neurological deficits is possible. Present treatment centers on the decision to administer tissue plasminogen activator, subsequent medical stabilization and early intervention with rehabilitation and risk factor management. The advent of stem cell therapy presents an exciting new frontier for research in stroke treatment, with the potential to cause a paradigm shift from symptomatic control and secondary prevention to reconstitution of neural networks and prevention of neuronal cell death after neurologic injury.

In vitro propagation and characterization of neoplastic stem/progenitor-like cells from human prostate cancer tissue

BACKGROUND

According to the cancer stem cell hypothesis, tumor growth is sustained by a subpopulation of cancer stem/progenitor-like cells. Self-renewal and high clonogenic potential are characteristics shared by normal stem and neoplastic stem/progenitor-like cells. We investigated whether human prostate cancer specimens contain cells with these properties.

METHODS

Self-renewal and clonogenic potential were assessed by serial passaging of spheres and colony formation, respectively. Gene expression was analyzed by real time PCR. Protein expression was detected by immunocytochemistry. The neoplastic nature of the cells was verified by detection of the TMPRSS2/ERG gene fusion expression.

RESULTS

The epithelial fraction isolated from surgical specimens generated colonies in 68% (19/28) of the patients. Laminin adhesion selected for cells with high clonogenic potential. The epithelial fraction from 85% (42/49) of the patients generated primary prostaspheres. Serial passaging of prostaspheres demonstrated their self-renewal capacity, which is also supported by their expression of the stem cell markers Oct-4, Nanog, Bmi-1, and Jagged-1 mRNA. Cells derived from prostaspheres were more clonogenic than the parental epithelial fraction. The pattern of mRNA expression in prostaspheres resembled that of the basal compartment of the prostate (CK5(+)/CK14(+)/CK19(high)/CK18(-/low)/c-met(+)/AR(-/low)/PSA(-/low)), but also included stem cell markers (CD49b(+)/CD49f(+)/CD44(+)/DeltaNp63(+)/Nestin(+)/CD133(+)). The distribution of marker expression in prostaspheres suggests their heterogeneous cell composition. Prostaspheres expressed significantly higher PSCA mRNA levels than the epithelial fraction.

CONCLUSION

Human prostate cancer specimens contain neoplastic cells with self-renewal and clonogenic potential, which can be enriched and perpetuated in prostaspheres. Prostaspheres should prove valuable for the identification of prostate cancer stem/progenitor-like cells.

The potential of hematopoietic growth factors for treatment of Alzheimer's disease: a mini-review

There are no effective interventions that significantly forestall or reverse neurodegeneration and cognitive decline in Alzheimer's disease. In the past decade, the generation of new neurons has been recognized to continue throughout adult life in the brain's neurogenic zones. A major challenge has been to find ways to harness the potential of the brain's own neural stem cells to repair or replace injured and dying neurons. The administration of hematopoietic growth factors or cytokines has been shown to promote brain repair by a number of mechanisms, including increased neurogenesis, anti-apoptosis and increased mobilization of bone marrow-derived microglia into brain. In this light, cytokine treatments may provide a new therapeutic approach for many brain disorders, including neurodegenerative diseases like Alzheimer's disease. In addition, neuronal hematopoietic growth factor receptors provide novel targets for the discovery of peptide-mimetic drugs that can forestall or reverse the pathological progression of Alzheimer's disease.

Production of neurospheres from CNS tissue

The relatively recent discovery of persistent adult neurogenesis has led to the experimental isolation and characterization of central nervous system neural stem cell populations. Protocols for in vitro analysis and expansion of neural stem cells are crucial for understanding their properties and defining characteristics. The methods described here allow for cell and molecular analysis of individual clones of cells--neurospheres--derived from neural stem/progenitor cells. Neurospheres can be cultivated from a variety of normal, genetically altered, or pathological tissue specimens, even with protracted postmortem intervals, for studies of mechanisms underlying neurogenesis, cell fate decisions, and cell differentiation. Neurosphere-forming cells hold great promise for the development of cell and molecular therapeutics for a variety of neurological diseases.

Role of Endogenous Neural Stem Cells in Neurological Disease and Brain Repair

These examples show that stem-cell-based therapy of neuro-psychiatric disorders will not follow a single scheme, but rather include widely different approaches. This is in accordance with the notion that the impact of stem cell biology on neurology will be fundamental, providing a shift in perspective, rather than introducing just one novel therapeutic tool. Stem cell biology, much like genomics and proteomics, offers a "view from within" with an emphasis on a theoretical or real potential and thereby the inherent openness, which is central to the concept of stem cells. Thus, stem cell biology influences many other, more traditional therapeutic approaches, rather than introducing one distinct novel form of therapy. Substantial advances have been made i n neural stemcell research during the years. With the identification of stem and progenitor cells in the adult brain and the complex interaction of different stem cell compartments in the CNS--both, under physiological and pathological conditions--new questions arise: What is the lineage relationship between t he different progenitor cells in the CNS and how much lineage plasticity exists? What are the signals controlling proliferation and differentiation of neural stem cells and can these be utilized to allow repair of the CNS? Insights in these questions will help to better understand the role of stem cells during development and aging and the possible relation of impaired or disrupted stem cell function and their impact on both the development and treatment of neurological disease. A number o f studies have indicated a limited neuronal and glial regeneration certain pathological conditions. These fundamental observations have already changed our view on understanding neurological disease and the brain's capacity for endogenous repair. The following years will have to show how we can influence andmodulate endogenous repair nisms by increasing the cellular plasticity in the young and aged CNS.

Stem Cells, Regenerative Medicine, and Animal Models of Disease

The field of stem cell biology and regenerative medicine is rapidly moving toward translation to clinical practice, and in doing so has become even more dependent on animal donors and hosts for generating cellular reagents and assaying their potential therapeutic efficacy in models of human disease. Advances in cell culture technologies have revealed a remarkable plasticity of stem cells from embryonic and adult tissues, and transplantation models are now needed to test the ability of these cells to protect at-risk cells and replace cells lost to injury or disease. With such a mandate, issues related to acceptable sources and controversial (e.g., chimeric) models have challenged the field to provide justification of their potential efficacy before the passage of new restrictions that may curb anticipated breakthroughs. Progress from the use of both in vitro and in vivo regenerative medicine models already offers hope both for the facilitation of stem cell phenotyping in recursive gene expression profile models and for the use of stem cells as powerful new therapeutic reagents for cancer, stroke, Parkinson's, and other challenging human diseases that result in movement disorders. This article describes research in support of the following three objectives: (1) To discover the best stem or progenitor cell in vitro protocols for isolating, expanding, and priming these cells to facilitate their massive propagation into just the right type of neuronal precursor cell for protection or replacement protocols for brain injury or disease, including those that affect movement such as Parkinson's disease and stroke; (2) To discover biogenic factors--compounds that affect stem/progenitor cells (e.g., from high-throughput screening and other bioassay approaches)--that will encourage reactive cell genesis, survival, selected differentiation, and restoration of connectivity in central nervous system movement and other disorders; and (3) To establish the best animal models of human disease and injury, using both small and large animals, for testing new regenerative medicine therapeutics.

Rat bone marrow progenitor cells transduced in situ by rSV40 vectors differentiate into multiple central nervous system cell lineages

Using bone marrow-directed gene transfer, we tested whether bone marrow-derived cells may function as progenitors of central nervous system (CNS) cells in adult animals. SV40-derived gene delivery vectors were injected directly into femoral bone marrow, and we examined transgene expression in blood and brain for 0-16 months thereafter by immunostaining for FLAG epitope marker. An average of 5% of peripheral blood cells and 25% of femoral marrow cells were FLAG(+) throughout the study. CNS FLAG-expressing cells were mainly detected in the dentate gyrus (DG) and periventricular subependymal zone (PSZ). Although absent before 1 month and rare at 4 months, DG and PSZ FLAG(+) cells were abundant 16 months after bone marrow injection. Approximately 5% of DG cells expressed FLAG, including neurons (48.6%) and microglia (49.7%), and occasional astrocytes (1.6%), as determined by double immunostaining for FLAG and lineage markers. These data suggest that one or more populations of cells resident within adult bone marrow can migrate to the brain and differentiate into CNS-specific cells.

Neuronal differentiation of human mesenchymal stem cells: Changes in the expression of the Alzheimer's disease-related gene seladin-1

Seladin-1 (SELective Alzheimer's Disease INdicator-1) is an anti-apoptotic gene, which is down-regulated in brain regions affected by Alzheimer's disease (AD). In addition, seladin-1 catalyzes the conversion of desmosterol into cholesterol. Disruption of cholesterol homeostasis in neurons may increase cell susceptibility to toxic agents. Because the hippocampus and the subventricular zone, which are affected in AD, are the unique regions containing stem cells with neurogenic potential in the adult brain, it might be hypothesized that this multipotent cell compartment is the predominant source of seladin-1 in normal brain. In the present study, we isolated and characterized human mesenchymal stem cells (hMSC) as a model of cells with the ability to differentiate into neurons. hMSC were then differentiated toward a neuronal phenotype (hMSC-n). These cells were thoroughly characterized and proved to be neurons, as assessed by molecular and electrophysiological evaluation. Seladin-1 expression was determined and found to be significantly reduced in hMSC-n compared to undifferentiated cells. Accordingly, the total content of cholesterol was decreased after differentiation. These original results demonstrate for the first time that seladin-1 is abundantly expressed by stem cells and appear to suggest that reduced expression in AD might be due to an altered pool of multipotent cells.

Multiple stem cell traits of expanded rat bone marrow stromal cells

Bone marrow stromal cells (BMSC) exhibit many traits of a stem cell population. Knowing that BMSC have the ability to self-renew, proliferate and differentiate into a variety of cell types, questions may arise as to whether these traits differ between the cells that have different expansion times. In this study, we examined the stem cell potentiality of BMSC through their characterization, proliferative capacity and the ability to differentiate into multiple lineages in the cultured 2nd passage cells and 10th passage cells. The results were as follows: (1) the 10th passage cells had a larger and more flatted morphology than the 2nd passage cells and also exhibited a decreased labeling for BMSC-related antigens such as CD90, CD73. (2) The cell proliferative capacity was approximately 2 times greater in the 2nd passage cells, and the apoptosis phenomenon was detected in the 10th passage cells. (3) The ability to differentiate into mesodermal tissue (osteocytes, adipocytes), as well as into ectodermal tissue (neurons) was more effective in the 2nd passage cells. Taken together, early stage BMSC would be a valuable cell source for various in vitro applications, as well as cell therapy.

Nikolaou K, Vrachnis N. Neurotrophin-3 and FLT3 tyrosine kinase receptor in perinatal life

Our aim is to determine—in 30 healthy full-term infants and their mothers—circulating levels of neurotrophin-3 (NT-3) (important for antenatal and postnatal brain development and implicated in the immune response) and FLT3 tyrosine kinase receptor (FLT3) (controlling hematopoiesis and found in the nervous tissue), in the fetal and neonatal life. NT-3 levels, in contrast to FLT3 ones, increased significantly on the fourth postnatal day in relation to the low levels found in the mother, fetus, and day 1 neonate (P = .03, respectively). Maternal and umbilical NT3 levels positively correlated with respective FLT3 levels (P = .003 and P = .03). Circulating NT-3 levels increased in early neonatal life, possibly due to exposure to various stimuli soon after birth. FLT3 levels do not seem to behave accordingly, although these two substances probably synergize.

Activation of the PI3-K/Akt pathway mediates cGMP enhanced-neurogenesis in the adult progenitor cells derived from the subventricular zone

The intracellular mechanisms that regulate neurogenesis remain unclear. Using neurospheres isolated from the subventricular zone (SVZ) of the adult rat, we investigated the effect of cyclic guanosine monophosphate (cGMP) and its signaling pathway on the induction of neurogenesis. Neurospheres expressed phosphodiesterase 5 (PDE5) and treatment of neurospheres with Sildenafil, a specific inhibitor of PDE5, significantly increased cGMP levels and neurogenesis. In addition, incubation of neurospheres with Sildenafil significantly phosphorylated Akt, which was associated with an increase of phosphorylation of glycogen synthase kinase 3 (GSK-3), a downstream target of Akt. Coincubation of neurospheres with Sildenafil and LY 294002, a pharmacological inhibitor of PI3-K/Akt, abolished Sildenafil-induced phosphorylated Akt and GSK-3. Furthermore, LY 294002 blocked Sildenafil-increased SVZ cell proliferation. These data suggest that Sildenafil-enhanced neurogenesis likely occurs through activation of the PI3-K/Akt/GSK-3 pathway.

Phenotypic and functional characterization of adult brain neuropoiesis

The modern concept of neurogenesis in the adult brain is predicated on the premise that multipotent glial cells give rise to new neurons throughout life. Although extensive evidence exists indicating that this is the case, the transition from glial to neuronal phenotype remains poorly understood. A unique monolayer cell-culture system was developed to induce, expose, and recapitulate the entire developmental series of events of subventricular zone (SVZ) neurogenesis. We show here, using immunophenotypic, ultrastructural, electrophysiological, and time-lapse analyses, that SVZ-derived glial fibrillary acidic protein(low)/A2B5+/nestin+ candidate founder cells undergo metamorphosis to eventually generate large numbers of fully differentiated interneuron phenotypes. A model of postnatal neurogenesis is considered in light of known embryonic events and reveals a limited developmental potential of SVZ stem/progenitor cells, whereby ancestral cells in both embryonic and postnatal/adult settings give rise to glia and GABAergic interneurons.

Cell proliferation and granule cell dispersion in human hippocampal sclerosis

Granule cell dispersion (GCD) is observed in approximately 40% of cases of hippocampal sclerosis (HS) in patients with epilepsy. Studies in animal models suggest that GCD may be a consequence of enhanced proliferation of granule cell precursors as a result of seizures. We quantified the number of cells in cycle in subfields of the hippocampus with immunohistochemistry for Mcm2 in 14 HS cases with or without severe GCD compared to 6 epilepsy patients without classical HS or GCD as well as 5 postmortem controls. Higher numbers of Mcm2-positive cells were seen in the region of the granule cell layer in patients with severe GCD, and immunolabeling with Geminin and Ki-67 confirmed a proportion were progressing through cycle. Double labeling with Mcm2 and GFAP confirmed the majority of these cycling cells were GFAP-negative and occasional cells stained colocalized with stem cell marker nestin. These findings support the view that GCD may be a phenomenon related to increased progenitor cell proliferation in patients with hippocampal damage and chronic epilepsy.

Transient expression of MIDC-8 in the normal mouse brain

In this study, we have immunohistochemically characterized the expression of mononuclear phagocyte markers CD14, CD36, CD68, CD204 and MARCO by parenchymal microglia in the developing and adult mouse brain. We further investigated whether these cells express two well-characterized phenotypic markers of dendritic cells: CD205 (DEC-205/NLDC-145) and MIDC-8 antigen. Our results confirm the lack of expression of dendritic cell markers by microglia. We noted that these cells do not appear to express markers associated with monocytes and macrophages during the course of development, but do express CD68 and CD204 antigens in the adult. Unexpectedly, we also noted the transient expression of MIDC-8 antigen on cells within the medial ganglionic eminence and by neuroepithelial cells lining the lateral ventricles and in the medial lemniscus between E15 and E19. We discuss this finding in the context of neural and haematopoietic differentiation.

Survival of mammary stem cells in suspension culture: implications for stem cell biology and neoplasia

There is increasing evidence that a variety of neoplasms including breast cancer may result from transformation of normal stem and progenitor cells. In the past, isolation and characterization of mammary stem cells has been limited by the lack of suitable culture systems able to maintain these cells in an undifferentiated state in vitro. We have recently described a culture system in which human mammary stem and progenitor cells are able to survive in suspension and produce spherical colonies composed of both stem and progenitor cells. Recent observation that adult stem cells from other tissues may also retain the capacity for growth under anchorage independent conditions suggests a common underlying mechanism. We propose that this mechanism involves the interaction between the canonical Wnt signal pathway and E-cadherin. The Wnt pathway has been implicated in normal stem cell self-renewal in vivo. Furthermore, there is evidence that deregulation of this pathway in the mammary gland and other organs may play a key role in carcinogenesis. Thus, the development of in vitro suspension culture systems not only provides an important new tool for the study of mammary cell biology, but also may have important implications for understanding key molecular pathways in both normal and neoplastic stem cells.

Erythropoietin gene from a teleost fish, Fugu rubripes

In this paper we report the cloning and characterization of the erythropoietin (Epo) gene from the pufferfish, Fugu rubripes. This is the first nonmammalian Epo gene to be cloned. The Fugu Epo comprises 5 exons and 4 introns similar to the human EPO, and encodes a 185–amino acid protein that is 32% to 34% identical to Epo from various mammals. The synteny of genes at the Epo locus is conserved between the Fugu and humans. Unlike in mammals in which adult kidney is the primary Epo-producing organ, the heart is the main Epo-producing organ in adult Fugu. In addition to the heart, Fugu Epo is also expressed in the liver and brain similar to the human EPO. Interestingly, the transcripts in the Fugu brain are generated from a distal promoter and include an alternatively spliced first coding exon. No such brain-specific alternative splicing of Epo has been reported in mammals so far. Transient transfection studies in a fish hepatoma cell line (PLHC-1) and a human hepatoma cell line (HepG2) suggest that although the Fugu Epo promoter many not be hypoxia inducible, the gene may be regulated by hypoxia.

Chemokines promote quiescence and survival of human neural progenitor cells

Many cell types in the brain express chemokines and chemokine receptors under homeostatic conditions, arguing for a role of these proteins in normal brain processes. Because chemokines have been shown to regulate hematopoietic progenitor cell proliferation, we hypothesized that chemokines would regulate neural progenitor cell (NPC) proliferation as well. Here we show that chemokines activating CXCR4 or CCR3 reversibly inhibit NPC proliferation in isolated cells, neurospheres, and in hippocampal slice cultures. Cells induced into quiescence by chemokines maintain their multipotential ability to form both neurons and astrocytes. The mechanism of chemokine action appears to be a reduction of extracellular signal-related kinase phosphorylation as well as an increase in Reelin expression. The inhibitory effects of chemokines are blocked by heparan sulfate and apolipoprotein E3 but not apolipoprotein E4, suggesting a regulatory role of these molecules on the effects of chemokines. Additionally, we found that the chemokine fractalkine promotes survival of NPCs. In addition to their role in chemotaxis, chemokines affect both the survival and proliferation of human NPCs in vitro. The presence of constitutively expressed chemokines in the brain argues that under homeostatic conditions, chemokines promote survival but maintain NPCs in a quiescent state. Our studies also suggest a link between inflammatory chemokine production and the inhibition of neurogenesis.

[Current concepts in stem cell research]

In the last few years, advances in stem cell research have opened up new horizons in the treatment of human diseases and in regenerative medicine. It is not unusual to find news on stem cell research in newspapers and other media. This review describes some basic concepts in research needed to understand the medical literature on stem cells and to provide the information and bibliography necessary to be up to date in one of the subjects that has generated the greatest number of publications in the last few years.

Stem cells in normal breast development and breast cancer

The main focus of this review is the role of mammary stem cells in normal breast development and carcinogenesis. We have developed a new in vitro culture system that permits, for the first time, the propagation of mammary stem and progenitor cells in an undifferentiated state, which should facilitate the elucidation of pathways that regulate normal mammary stem-cell self-renewal and differentiation. Furthermore, we propose a model in which transformation of stem cells, or early progenitor cells, results in carcinogenesis. A key event in this process is the deregulation of normal self-renewal in these cells. Transformed mammary stem or progenitor cells undergo aberrant differentiation processes that result in generation of the phenotypic heterogeneity found in human and rodent breast cancers. This phenotypic diversity is driven by a small subset of mammary tumour stem cells. We will discuss the important implications of this mammary tumour stem-cell model.

Functional integration of embryonic stem cell-derived neurons in hippocampal slice cultures

The generation of neurons and glia from pluripotent embryonic stem (ES) cells represents a promising strategy for the study of CNS development and repair. ES cell-derived neural precursors have been shown to develop into morphologically mature neurons and glia when grafted into brain and spinal cord. However, there is a surprising shortage of data concerning the functional integration of ES cell-derived neurons (ESNs) into the host CNS tissue. Here, we use ES cells engineered to express enhanced green fluorescent protein (EGFP) only in neuronal progeny to study the functional properties of ESNs during integration into long-term hippocampal slice cultures. After incorporation into the dentate gyrus, EGFP+ donor neurons display a gradual maturation of their intrinsic discharge behavior and a concomitant increase in the density of voltage-gated Na+ and K+ channels. Integrated ESNs express AMPA and GABA(A) receptor subunits. Most importantly, neurons derived from ES cells receive functional glutamatergic and GABAergic synapses from host neurons. Specifically, we demonstrate that host perforant path axons form synapses onto integrated ESNs. These synapses between host and ES cell-derived neurons display pronounced paired-pulse facilitation indicative of intact presynaptic short-term plasticity. Thus, ES cell-derived neural precursors generate functionally active neurons capable of integrating into the brain circuitry.

Environment temperature affects cell proliferation in the spinal cord and brain of juvenile turtles

The spinal cords and brains--comprising dorsal cortex (DC), medial cortex (MC) and diencephalon (Dien)--of juvenile turtles acclimated to warm temperature [27-30 degrees C; warm-acclimated turtles (WATs)] revealed higher density values of bromodeoxyuridine-labeled cells (BrdU-LCs) than those acclimated to a cooler environment [5-14 degrees C; cold-acclimated turtles (CATs)]. Both populations were under the influence of the seasonal daily light-dark rhythms. Pronounced differences between WATs and CATs (independent t-test; confidence level, P<0.01) were found in the central area of the spinal gray matter and in the ependymal epithelium lining the brain ventricles. Forebrain regions (DC, MC and Dien) also revealed significant differences between WATs and CATs (independent t-test; confidence level, P<0.01-0.05). Unexplored biological clocks that may be affecting cell proliferation were equalized by performing paired experiments involving one WAT and one CAT. Both animals were injected on the same day at the same time and both were sacrificed 24 h later. These experiments confirmed that a warm environment increased cell proliferation in the CNS of turtles. Double- and triple-labeling experiments involving anti-BrdU antibody together with anti-glial protein antibodies revealed that temperature modulates not only cell populations expressing glial markers but also other cells that do not express them. As expected, in the case of short post-injection (BrdU) surviving time points, no cells were found colabeling for BrdU and NeuN (neuronal marker). The probable direct effect of temperature on the cell division rate should be analyzed together with potential indirect effects involving increased motor activity and increased food intake. The fate of the increased BrdU-LCs (death, permanence as progenitor cells or differentiation following neuronal or glial lines) remains a matter for further investigation. Results are discussed in the light of current opinions concerned with post-natal neurogenesis in vertebrates.

Upregulation of neurogenesis and reduction in functional deficits following administration of DEtA/NONOate, a nitric oxide donor, after traumatic brain injury in rats

OBJECT

Neurogenesis, which is upregulated by neural injury in the adult mammalian brain, may be involved in the repair of the injured brain and functional recovery. Therefore, the authors sought to identify agents that can enhance neurogenesis after brain injury, and they report that (Z)-1-[N-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate (DETA/NONOate), a nitric oxide donor, upregulates neurogenesis and reduces functional deficits after traumatic brain injury (TBI) in rats.

METHODS

The agent DETA/NONOate (0.4 mg/kg) was injected intraperitoneally into 16 rats daily for 7 days, starting 1 day after TBI induced by controlled cortical impact. Bromodeoxyuridine (100 mg/kg) was also injected intraperitoneally daily for 14 days after TBI to label the newly generated cells in the brain. A neurological functional evaluation was performed in all rats and the animals were killed at 14 or 42 days postinjury. Immunohistochemical staining was used to identify proliferating cells.

CONCLUSIONS

Compared with control rats, the proliferation, survival, migration and differentiation of neural progenitor cells were all significantly enhanced in the hippocampus, subventricular zone, striatum, corpus callosum, and the boundary zone of the injured cortex, as well as in the contralateral hemisphere in rats with TBI that received DETA/ NONOate treatment. Neurological functional outcomes in the DETA/NONOate-treated group were also significantly improved compared with the untreated group. These data indicate that DETA/NONOate may be useful in the treatment of TBI.

Astrocytes as stem cells: nomenclature, phenotype, and translation

Recently discovered multipotent astrocytic stem cells are discussed in light of current nomenclature for glial precursor and lineage-associated cells in the developing, postnatal, and adult mammalian brain. Defining the phenotype of any immature cell in the nervous system is a challenge, and a position is stated that includes the need for categorizing cells within a continuum of differentiation potential. The possibility for dedifferentiating glial cells into clonogenic stem-like cells offers numerous possibilities for translating knowledge and technology from this subfield of stem cell biology to regenerative medicine. Along with the need for developing a new lexicon for defining the cellular players that contribute to the generation of glia and neurons in the developing and mature central nervous system, the relationships also need to be established among potency, repopulation attempts, and tumorigenesis of cells meeting the criteria of glial stem cells. Finally, it is possible that understanding the normal differentiation, de- and transdifferentiation potential of glial stem-like cells in the mature central nervous system will provide insights into the possible use of these cells, or biogenic factors associated with their growth and differentiation, in therapeutic approaches for a variety of neurological disorders.

In vitro propagation and transcriptional profiling of human mammary stem/progenitor cells

Although the existence of mammary stem cells has been suggested by serial transplantation studies in mice, their identification has been hindered by the lack of specific surface markers, and by the absence of suitable in vitro assays for testing stem cell properties: self-renewal and ability to generate differentiated progeny. We have developed an in vitro cultivation system that allows for propagation of human mammary epithelial cells (HMECs) in an undifferentiated state, based on their ability to proliferate in suspension, as nonadherent mammospheres. We demonstrate that nonadherent mammospheres are enriched in early progenitor/stem cells and able to differentiate along all three mammary epithelial lineages and to clonally generate complex functional structures in reconstituted 3D culture systems. Gene expression analysis of cells isolated from nonadherent mammospheres revealed overlapping genetic programs with other stem and progenitor cells and identified new markers that may be useful in the identification of mammary stem cells. The isolation and characterization of these stem cells should help elucidate the molecular pathways that govern normal mammary development and carcinogenesis.

Neural stem cells: an overview

This review focuses on the nature and functional properties of stem cells of the adult mammalian central nervous system (CNS). It has recently been shown that cell turnover, including neurons, does occur in the mature CNS, thanks to the persistence of precursor cells that possess the functional characteristics of bona-fide neural stem cells (NSCs) within restricted brain areas. We discuss how the subventricular zone of the forebrain (SVZ) is the most active neurogenetic area and the richest source of NSCs. These NSCs ensure a life-long contribution of new neurons to the olfactory bulb and, when placed in culture, can be grown and extensively expanded for months, allowing the generation of stem cell lines, which maintain stable and constant functional properties. A survey of the differentiation potential of these NSCs, both in vitro and in vivo, outlines their extreme plasticity that seems to outstretch the brain boundaries, so that these neuroectodermal stem cells may give rise to cells that derive from developmentally distinct tissues. A critical discussion of the latest, controversial findings regarding this surprising phenomenon is provided.

Leukemia inhibitory factor is a key signal for injury-induced neurogenesis in the adult mouse olfactory epithelium

The mammalian olfactory epithelium (OE) is composed of primary olfactory sensory neurons (OSNs) that are renewed throughout adulthood by local, restricted neuronal progenitor cells. The molecular signals that control this neurogenesis in vivo are unknown. Using olfactory bulb ablation (OBX) in adult mice to trigger synchronous mitotic stimulation of neuronal progenitors in the OE, we show the in vivo involvement of a cytokine in the cellular events leading to the regeneration of the OE. We find that, of many potential mitogenic signals, only leukemia inhibitory factor (LIF) is induced before the onset of neuronal progenitor proliferation. The rise in LIF mRNA expression peaks at 8 hr after OBX, and in situ RT-PCR and immunocytochemistry indicate that LIF is upregulated, in part, in the injured neurons themselves. This rise in LIF is necessary for injury-induced neurogenesis, as OBX in the LIF knock-out mouse fails to stimulate cell proliferation in the OE. Moreover, delivery of exogenous LIF to the intact adult OE using an adenoviral vector stimulates BrdU labeling in the apical OE. Taken together, these results suggest that injured OSNs release LIF as a stimulus to initiate their own replacement.

Rasayanas: evidence for the concept of prevention of diseases

Rasayanas are non-toxic Ayurvedic complex herbal preparations or individual herbs used to rejuvenate or attain the complete potential of an individual in order to prevent diseases and degenerative changes that leads to disease. The present paper reviews various activities of rasayanas to support the above concept, its role as a prophylactic medication and significance in the prevention of diseases in both healthy as well as diseased individuals. The emerging data suggest that the possible mechanisms may be by immunostimulation, quenching free radicals, enhancing cellular detoxification mechanisms, repair damaged non-proliferating cells, inducing cell proliferation and self-renewal of damaged proliferating tissues, and replenishing them by eliminating damaged or mutated cells with fresh cells.

The role of cell therapy for stroke

Cellular therapy has been evaluated in small animals, subhuman primates, and now humans for the potential repair of brain injury due to stroke. Experimental striate stroke models have proven useful for the purpose of evaluating different treatment paradigms. Early clinical trials involving neuronal transplantation in patients suffering motor-related stroke in the basal ganglia region have begun.

This research will be described in this report.

Ammon's horn sclerosis: a maldevelopmental disorder associated with temporal lobe epilepsy

Ammon's horn sclerosis (AHS) is the major neuropathological substrate in patients with temporal lobe epilepsy (TLE). Histopathological hallmarks include segmental loss of pyramidal neurons, granule cell dispersion and reactive gliosis. Pathogenetic mechanisms underlying this distinct hippocampal pathology have not yet been identified and it remains to be resolved whether AHS represents the cause or the consequence of chronic seizure activity and pharmacoresistant TLE. Whereas the clinical history indicates an early onset in most patients, ie, occurrence of febrile seizures at a young age, surgical treatment is usually carried out at an end stage of the disease. It has, therefore, been difficult to analyse the sequential development of hippocampal pathology in TLE patients. Recent molecular neuropathological studies focusing on developmental aspects of hippocampal organization revealed 2 intriguing findings in AHS specimens: i) The persistence of Cajal-Retzius cells in AHS patients points towards an early insult and an altered Reelin signaling pathway and ii) increased neurogenesis in and abnormal architectural organization of the dentate granule cell layer can be observed in young patients with early hippocampal seizure onset. These findings would be compatible with a model that involves a neurodevelopmental component in the formation of AHS. Its association with a lowered seizure threshold and an increased susceptibility for segmental cell loss in the hippocampus during the long course of the disease may constitute additional elements in a pathogenic cascade.

Neural cells derived from adult bone marrow and umbilical cord blood

Under experimental conditions, tissue-specific stem cells have been shown to give rise to cell lineages not normally found in the organ or tissue of residence. Neural stem cells from fetal brain have been shown to give rise to blood cell lines and conversely, bone marrow stromal cells have been reported to generate skeletal and cardiac muscle, oval hepatocytes, as well as glia and neuron-like cells. This article reviews studies in which cells from postnatal bone marrow or umbilical cord blood were induced to proliferate and differentiate into glia and neurons, cellular lineages that are not their normal destiny. The review encompasses in vitro and in vivo studies with focus on experimental variables, such as the source and characterization of cells, cell-tracking methods, and markers of neural differentiation. The existence of stem/progenitor cells with previously unappreciated proliferation and differentiation potential in postnatal bone marrow and in umbilical cord blood opens up the possibility of using stem cells found in these tissues to treat degenerative, post-traumatic and hereditary diseases of the central nervous system.

Human cortical glial tumors contain neural stem-like cells expressing astroglial and neuronal markers in vitro

Neural stem cells from neurogenic regions of mammalian CNS are clonogenic in an in vitro culture system exploiting serum and anchorage withdrawal in medium supplemented with methyl cellulose and the pleiotropic growth factors EGF, FGF2, and insulin. The aim of this study was to test whether cortical glial tumors contain stem-like cells capable, under this culture system, of forming clones showing intraclonal heterogeneity in the expression of neural lineage-specific proteins. The high frequencies of clone-forming cells (about 0.1-10 x 10(-3)) in clinical tumor specimens with mutated p53, and in neurogenic regions of normal human CNS, suggest that the ability to form clones in this culture system is induced epigenetically. RT-PCR analyses of populations of normal brain- and tumor-derived sister clones revealed transcripts for nestin, neuron-specific enolase, and glial fibrillary acidic protein (GFAP). However, the tumor-derived clones were different from clones derived from neurogenic regions of normal brain in the expression of transcripts specific for genes associated with neural cell fate determination via the Notch-signaling pathway (Delta and Jagged), and cell survival at G2 or mitotic phases (Survivin). Moreover, the individual glioma-derived clones contain cells immunopositive separately for GFAP or neuronal beta-III tubulin, as well as single cells coexpressing both glial and neuronal markers. The data suggest that the latent critical stem cell characteristics can be epigenetically induced by growth conditions not only in cells from neurogenic regions of normal CNS but also in cells from cortical glial tumors. Moreover, tumor stem-like cells with genetically defective responses to epigenetic stimuli may contribute to gliomagenesis and the developmental pathological heterogeneity of glial tumors.

A paradigm shift in neurorehabilitation

The practice of neurorehabilitation in the clinic has undergone a paradigm shift as a result of influences from basic and clinical research. I have identified six areas of knowledge that by advancing so rapidly have brought about this paradigm shift: first, the increased understanding of how the CNS is reorganised after training or injury; second, the knowledge of how declarative and procedural memory operates and how this can influence rehabilitation therapy; third, a greater appreciation of the chemical factors that promote learning and neural remodelling; fourth, the fact that computational neuroscience can teach us how complex behaviour can emerge from the interaction of thousands of neurons; fifth, the influence of evidence-based medicine on neurorehabilitation; and sixth, the importance of reliable outcome measures for both injury and treatment. These are young scientific disciplines that offer great opportunities for further research. The complexity of neurorehabilitation will also require greater attention to a substantially neglected problem, the incorporation of techniques that have been proven effective in clinical trials into routine and effective clinical practice.

Increase of nestin-immunoreactive neural precursor cells in the dentate gyrus of pediatric patients with early-onset temporal lobe epilepsy

A considerable potential for neurogenesis has been identified in the epileptic rat hippocampus. Here, we explore this feature in human patients suffering from chronic mesial temporal lobe epilepsy. Immunohistochemical detection of the neurodevelopmental antigen nestin was used to detect neural precursor cells, and cell-type specific markers were employed to study their histogenetic origin and potential for neuronal or glial differentiation. The ontogenetic regulation of nestin-positive precursors was established in human control brains (week 19 of gestation-15 years of age). A striking increase of nestin-immunoreactive cells within the hilus and dentate gyrus could be observed in a group of young patients with temporal lobe epilepsy (TLE) and surgical treatment before age 2 years compared to adult TLE patients and controls. The cellular morphology and regional distribution closely resembled nestin-immunoreactive granule-cell progenitors transiently expressed during prenatal human hippocampus development. An increased Ki-67 proliferation index and clusters of supragranular nestin-immunoreactive cells within the molecular layer of the dentate gyrus were also noted in the group of young TLE patients. Confocal studies revealed colocalization of nestin and the betaIII isoform of tubulin, indicating a neuronal fate for some of these cells. Vimentin was consistently expressed in nestin-immunoreactive cells, whereas cell lineage-specific markers, i.e., glial fibrillary acidic protein, MAP2, neurofilament protein, NeuN, or calbindin D-28k failed to colocalize. These findings provide evidence for increased neurogenesis in pediatric patients with early onset of temporal lobe epilepsy and/or point towards a delay in hippocampal maturation in a subgroup of patients with TLE.

Neural transplantation for stroke

Tremendous achievements in neuroscience over the past three decades have provided a solid foundation for basic and clinical research in neurotransplantation. Restorative neurosurgical procedures will develop from different directions, and it is likely that a combination of approaches will be necessary to maximise patient outcomes. We believe that cerebral infarction and selected neurodegenerative disorders are appropriate initial candidates for this research.

Stem cells and neuropoiesis in the adult human brain

Stem cells in adult tissues have attracted a great deal of interest. These cells are self-renewing and can give rise to diverse progeny. An extraordinary finding was the presence of stem cells in the mature human brain. This tissue was previously believed incapable of generating new neurons, but neuropoiesis is now an established phenomenon in the adult brains of mammals, including human beings. This persistent neurogenesis has potential therapeutic applications for various neurological disorders as a source for tissue engraftment and as self-repair by a person's own indigenous population of pluripotent cells or biogenic by-products of their proliferation and differentiation.

Reduced hippocampal neurogenesis in adult transgenic mice with chronic astrocytic production of interleukin-6

Postnatal neurogenesis can be modulated after brain injury, but the role of the attendant expression of inflammatory mediators in such responses remains to be determined. Here we report that transgenically directed production of interleukin-6 (IL-6) by astroglia decreased overall neurogenesis by 63% in the hippocampal dentate gyrus of young adult transgenic mice. The proliferation, survival, and differentiation of neural progenitor cells labeled with the thymidine analog bromodeoxyuridine were all reduced in the granule cell layer of these mice, whereas their distribution and gliogenesis appeared normal. These effects were not a consequence of general toxicity of the IL-6 transgene, because they were manifested in the absence of neuronal death and of major changes in glial cell number and morphology. These findings suggest that long-term exposure of the brain to proinflammatory mediators such as IL-6, as is seen in certain degenerative disorders and infections, can interfere with adult neurogenesis.

Rna-binding protein Musashi2: developmentally regulated expression in neural precursor cells and subpopulations of neurons in mammalian CNS

Musashi1 (Msi1) is a mammalian neural RNA-binding protein highly enriched in neural precursor cells that are capable of generating both neurons and glia during embryonic and postnatal CNS development. Here, we identified Musashi2 (Msi2), a novel mammalian RNA-binding protein that exhibits high sequence similarity to Msi1. The Msi2 transcript appeared to be distributed ubiquitously in a wide variety of tissues, consistent with the mRNA distribution of its Xenopus homolog, xrp1. However, the present study revealed cell type-specific and developmentally regulated expression of Msi2 in the mammalian CNS. Interestingly, Msi2 was expressed prominently in precursor cells in the ventricular zone and subventricular zone with the same pattern as Msi1 throughout CNS development. In the postnatal and adult CNS, this concurrent expression of Msi2 and Msi1 was seen in cells of the astrocyte lineage, including ependymal cells, a possible source for postnatal CNS stem cells. During neurogenesis, the expression of both Msi2 and Msi1 was lost in most postmitotic neurons, whereas Msi2 expression persisted in a subset of neuronal lineage cells, such as parvalbumin-containing GABA neurons in the neocortex and neurons in several nuclei of the basal ganglia. Msi2 may have a unique role that is required for the generation and/or maintenance of specific neuronal lineages. Furthermore, in vitro studies showed that Msi2 and Msi1 have similar RNA-binding specificity. These two RNA-binding proteins may exert common functions in neural precursor cells by regulating gene expression at the post-transcriptional level.

Distinct expression pattern of microtubule-associated protein-2 in human oligodendrogliomas and glial precursor cells

Microtubule-associated protein 2 (MAP2), a protein linked to the neuronal cytoskeleton in the mature central nervous system (CNS), has recently been identified in glial precursors indicating a potential role during glial development. In the present study, we systematically analyzed the expression of MAP2 in a series of 237 human neuroepithelial tumors including paraffin-embedded specimens and tumor tissue microarrays from oligodendrogliomas, mixed gliomas, astrocytomas, glioblastomas, ependymomas, as well as dysembryoplastic neuroepithelial tumors (DNT), and central neurocytomas. In addition, MAP2-immunoreactive precursor cells were studied in the developing human brain. Three monoclonal antibodies generated against MAP2A-B or MAP2A-D isoforms were used. Variable immunoreactivity for MAP2 could be observed in all gliomas with the exception of ependymomas. Oligodendrogliomas exhibited a consistently strong and distinct pattern of expression characterized by perinuclear cytoplasmic staining without significant process labeling. Tumor cells with immunoreactive bi- or multi-polar processes were mostly encountered in astroglial neoplasms, whereas the small cell component in neurocytomas and DNT was not labeled. These features render MAP2 immunoreactivity a helpful diagnostic tool for the distinction of oligodendrogliomas and other neuroepithelial neoplasms. RT-PCR, Western blot analysis, and in situ hybridization confirmed the expression of MAP2A-C (including the novel MAP2+ 13 transcript) in both oligodendrogliomas and astrocytomas. Double fluorescent laser scanning microscopy showed that GFAP and MAP2 labeled different tumor cell populations. In embryonic human brains, MAP2-immunoreactive glial precursor cells were identified within the subventricular or intermediate zones. These precursors exhibit morphology closely resembling the immunolabeled neoplastic cells observed in glial tumors. Our findings demonstrate MAP2 expression in astrocytic and oligodendroglial neoplasms. The distinct pattern of immunoreactivity in oligodendrogliomas may be useful as a diagnostic tool. Since MAP2 expression occurs transiently in migrating immature glial cells, our findings are in line with an assumed origin of diffuse gliomas from glial precursors.

The FLT3 tyrosine kinase receptor inhibits neural stem/progenitor cell proliferation and collaborates with NGF to promote neuronal survival

The FLT3 receptor tyrosine kinase (FLT3) was originally identified on hematopoietic stem cells (HSCs) and its ligand (FL) induces HSC proliferation. As stem cells originating from various tissues are more similar than once thought, the goal of this study was to determine whether neural stem cells express FLT3 and proliferate in response to FL. In fact, a subset of neural stem/progenitor cells does express FLT3, but contrary to our expectations, FL inhibited EGF and FGF-2 stimulated proliferation. Since FLT3 is expressed weakly by proliferative neuroepithelia but strongly by subsets of neurons in the CNS and PNS, we tested its ability to support neuronal survival. FL synergized with NGF to promote the survival of cultured DRG neurons, although it lacked any neurotrophic activity alone. We conclude that FL serves as an adjunct trophic factor in the nervous system, which differs from its role in the hematopoietic system.