Adult retinal pigment epithelium cells express neural progenitor properties and the neuronal precursor protein doublecortin

The adult mammalian retina is devoid of any detectable neurogenesis. However, different cell types have been suggested to potentially act as neural progenitors in the adult mammalian retina in vitro, such as ciliary body (CB), Muller glia, and retinal pigment epithelium (RPE) cells. In rodents and humans, strong evidence for neural stem or progenitor properties exists only for CB-derived cells, but not for other retinal cell types. Here, we provide a comparative analysis of adult rat CB- and RPE-derived cells suggesting that the two cell types share certain neural progenitor properties in vitro. CB and RPE cells expressed neural progenitor markers such as Nestin, Flk-1, Hes1, and Musashi. They proliferated under adherent and neurosphere conditions and showed limited self-renewal. Moreover, they differentiated into neuronal and glial cells based on the expression of differentiation markers such as the young neuronal marker beta-III tubulin and the glial and progenitor markers GFAP and NG2. Expression of beta-III tubulin was found in cells with neuronal and non-neuronal morphology. A subpopulation of RPE- and CB-derived progenitor cells expressed the neurogenesis-specific protein doublecortin (DCX). Interestingly, DCX expression defined a beta-III tubulin-positive CB and RPE fraction with a distinct neuronal morphology. In summary, the data suggest that RPE cells share with CB cells the potential to de-differentiate into a cell type with neural progenitor-like identity. In addition, DCX expression might define the neuronal-differentiating RPE- and CB-derived progenitor population.

Increased neurogenesis and the ectopic granule cells after intrahippocampal BDNF infusion in adult rats

There is evidence that BDNF influences the birth of granule cells in the dentate gyrus, which is one of the few areas of the brain that demonstrates neurogenesis throughout life. However, studies to date have not examined this issue directly. To do so, we compared the effects of BDNF, phosphate-buffered saline (PBS), or bovine serum albumin (BSA) on neurogenesis after infusion into the hippocampus of the normal adult rat, using osmotic pumps that were implanted unilaterally in the dorsal hilus. BDNF, PBS, and BSA were infused for 2 weeks. The mitotic marker bromodeoxyuridine (BrdU) was administered twice daily during the 2-week infusion period. At least 1 month after infusion ended, brains were processed immunocytochemically using antibodies to BrdU, a neuronal nuclear protein (NeuN), or calbindin D28K (CaBP), which labels mature granule cells. Stereology was used to quantify BrdU-labeled cells in the dorsal hippocampus that were double-labeled with NeuN or CaBP. There was a statistically significant increase in BrdU(+)/NeuN(+) double-labeled cells in the granule cell layer after BDNF infusion relative to controls. The values for BrdU(+)/NeuN(+) cells were similar to BrdU(+)/CaBP(+) cells, indicating that most new neurons were likely to be granule cells. In addition, BrdU(+)/NeuN(+)-labeled cells developed in the hilar region after BDNF infusion, which have previously only been identified after severe continuous seizures (status epilepticus) and associated pathological changes. Remarkably, neurogenesis was also increased contralaterally, but BDNF did not appear to spread to the opposite hemisphere. Thus, infusion of BDNF to a local area can have widespread effects on hippocampal neurogenesis. The results demonstrate that BDNF administration to the dentate gyrus leads to increased neurogenesis of granule cells. They also show that ectopic granule cells develop after BDNF infusion, which suggests that ectopic migration is not necessarily confined to pathological conditions. These results are discussed in light of the evidence that BDNF increases neuronal activity in hippocampus. Thus, the mechanisms underlying neurogenesis following BDNF infusion could be due to altered activity as well as direct effects of BDNF itself, and this is relevant to studies of other growth factors because many of them have effects on neuronal excitability that are often not considered.

Therapeutic potential of stem cells in perinatal medicine

Increasing evidence suggests that stem cells have tremendous potential to facilitate repair of damaged tissue and to exert protective influences that limit the extent of damage. Their inherent capacity to respond to signals generated by damaged tissue, migrate to these regions and either replace dead tissue or deliver protection by secretion of specific growth hormones and protective factors, suggests that they might have unrivalled therapeutic potential in perinatal medicine. A further potential of stem cells is their use in gene repair strategies for genetic disorders; an application which is exceedingly interesting from a perinatal perspective. Because of the relatively small size of infants and their capacity for future growth, stem cell therapy could be more successful in newborns than in older children or adults. In practical terms, the placenta, with its large reservoir of fetal blood, offers the ideal source of autologous stem cells. This affords the opportunity for stem cells to be collected and used, either directly ex vivo or after in vitro modulation, both for disorders in the neonatal period and for those arising later in life. The organs most affected from tissue damage in the neonatal period are the brain and the lung. So far, the most promising application of stem cells might be in the treatment of neurological injury. In this review we discuss recent research findings with adult stem cell therapy and their potential use in perinatal medicine. Furthermore, specific animal models suitable to explore the patho-physiological mechanisms of stem cell transplantation after neurological injury will be discussed. This review gives an overview of basic science findings and their possible role for clinical application with regards to the therapeutic potential of stem cells in perinatal medicine. Medline was searched for journal selection in peer-reviewed journals with high impact scores, which were relevant to this topic. All articles were in English and the search was not limited by publication year. However, the oldest publication was dated 1988 (reference 1).

Human embryoid body-derived stem cells in bladder regeneration using rodent model

OBJECTIVES

To evaluate the capability of a human embryonic germ (hEG) cell-derived cell line (SDEC), previously characterized in our laboratory, seeded on porcine small intestinal submucosa (SIS) to regenerate the injured rat bladder.

METHODS

Fluorescent-labeled SDEC cells seeded on SIS for 8 days in vitro were used as bladder grafts in rats. A total of 30 congenitally athymic rats (six groups of 5 rats each), underwent partial cystectomy and replacement with plain SIS (groups 1 to 3) or cell-seeded SIS (groups 4 to 6). The rats were sacrificed after 7 (groups 1 and 4), 14 (groups 2 and 5), and 28 (groups 3 and 6) days. The bladders were analyzed by histopathologic examination and fluorescence microscopy.

RESULTS

No graft rejection or diminution in bladder capacity occurred. Plain SIS implants had multiple calcareous deposits, not seen with the cell-seeded implants. Macroscopically, at 7 days, the grafts were healed with a cellular lining on the luminal aspect in groups 4 to 6. Microscopically, the rat bladder was completely regenerated 28 days after stem cell-seeded SIS implantation. Labeled stem cells were identified throughout the graft and contributed significantly to bladder regeneration.

CONCLUSIONS

The results of this study have demonstrated the successful replacement of a bladder defect in a rat model using hEG cell-derived cells seeded on SIS grafts. Longer term analysis of these bladder grafts will allow evaluation of function, cell migration, and differentiation processes of human stem cells.

Photoreceptor differentiation and integration of retinal progenitor cells transplanted into transgenic rats

Previous studies evaluating neural stem cells transplanted into the mature retina have demonstrated limited levels of graft-host integration and photoreceptor differentiation. The purpose of this investigation is to enhance photoreceptor cell differentiation and integration of retinal progenitor cells (RPC) following subretinal transplantation into retinal degenerate rats by optimization of isolation, expansion, and transplantation procedures. RPCs were isolated from human placental alkaline phosphatase (hPAP)-positive embryonic day 17 (E17) rat retina and expanded in serum-free defined media. RPCs at passage 2 underwent in vitro induction with all trans retinoic acid or were transplanted into the subretinal space of post-natal day (P) 17 S334ter-3 and S334ter-5 transgenic rats. Animals were examined post-operatively by ophthalmoscopy and optical coherence tomography (OCT) at weeks 1 and 4. Differentiation profiles of RPCs, both in vitro and in vivo were analysed microscopically by immunohistochemistry for various retinal cell specific markers. Our results demonstrated that the majority of passage 2 RPCs differentiated into retina-specific neurons expressing rhodopsin after in vitro induction. Following subretinal transplantation, grafted cells formed a multi-layer cellular sheet in the subretinal space in both S334ter-3 and S334ter-5 rats. Prominent retina-specific neuronal differentiation was observed in both rat lines as evidenced by recoverin or rhodopsin staining in 80% of grafted cells. Less than 5% of the grafted cells expressed glial fibrillary acidic protein. Synapsin-1 (label for nerve terminals) positive neural processes were present at the graft-host interface. Expression profiles of the grafted RPCs were similar to those of RPCs induced to differentiate in vitro using all-trans retinoic acid. In contrast to our previous study, grafted RPCs can demonstrate extensive rhodopsin expression, organize into layers, and show some features of apparent integration with the host retina following subretinal transplantation in slow and fast retinal degenerate rats. The similarity of the in vitro and in vivo RPC differentiation profiles suggests that intrinsic signals may have a significant contribution to RPC cell fate determination.

How to make a placenta: Mechanisms of trophoblast cell differentiation in mice – A Review

The word placenta is derived from the Latin term meaning 'flat cake'. Despite the rather humble name, the placenta is an amazing organ that forms both the interface for selective delivery of nutrients from the mother to the fetus and also re-directs maternal metabolic, endocrine, cardiovascular and immune functions to promote fetal survival and growth. These two functions are fulfilled by different specialized trophoblast cell subtypes, and my laboratory has been studying how their formation and functions are regulated during placental development. Through molecular studies in cultured cells and tissues, genetic studies in mice, and comparative analysis of placentas from humans, rodents and farm animals, it is now possible to describe molecular pathways that control the development of all major trophoblast cell subtypes and structures of the placenta. The work has revealed an intricate complexity of cell-cell interactions, environmental factors, and molecular networks that control normal development.

Large-scale identification of proteins expressed in mouse embryonic stem cells

A protein subset expressed in the mouse embryonic stem (ES) cell line, E14-1, was characterized by mass spectrometry-based protein identification technology and data analysis. In total, 1790 proteins including 365 potential nuclear and 260 membrane proteins were identified from tryptic digests of total cell lysates. The subset contained a variety of proteins in terms of physicochemical characteristics, subcellular localization, and biological function as defined by Gene Ontology annotation groups. In addition to many housekeeping proteins found in common with other cell types, the subset contained a group of regulatory proteins that may determine unique ES cell functions. We identified 39 transcription factors including Oct-3/4, Sox-2, and undifferentiated embryonic cell transcription factor I, which are characteristic of ES cells, 88 plasma membrane proteins including cell surface markers such as CD9 and CD81, 44 potential proteinaceous ligands for cell surface receptors including growth factors, cytokines, and hormones, and 100 cell signaling molecules. The subset also contained the products of 60 ES-specific and 41 stemness genes defined previously by the DNA microarray analysis of Ramalho-Santos et al. (Ramalho-Santos et al., Science 2002, 298, 597-600), as well as a number of components characteristic of differentiated cell types such as hematopoietic and neural cells. We also identified potential post-translational modifications in a number of ES cell proteins including five Lys acetylation sites and a single phosphorylation site. To our knowledge, this study provides the largest proteomic dataset characterized to date for a single mammalian cell species, and serves as a basic catalogue of a major proteomic subset that is expressed in mouse ES cells.

[A study of association between age-related circulating endothelial progenitor cells and arterial elasticity]

OBJECTIVE

Reduced arterial elasticity is a hallmark of aging in healthy humans independently of diseases and endothelial-cell injury and dysfunction may be responsible for this fall in arterial elasticity. We hypothesized that circulating endothelial progenitor cells (EPCs) are involved in endothelial repair and that lack of EPCs contributes to impaired arterial elasticity.

METHODS

A total of 56 healthy male volunteers were divided into young (n = 26) and elderly (n = 30) groups. Large and small artery elasticity indices were non-invasively assessed by using pulse wave analysis. Flow cytometer was used to count the number of circulating CD34(+) mononuclear cells (MNCs), which were isolated from peripheral blood by Ficoll density gradient centrifugation, and then the cells were plated on fibronectin-coated culture dishes. EPCs were characterized as adherent cells double positive staining for DiI-acLDL uptake and lectin binding with using fluorescent microscope.

RESULTS

C(1) (large artery elasticity index) and C(2) (small artery elasticity index) were significantly reduced in the elderly group compared with those in the young group (11.73 +/- 1.45 vs 16.89 +/- 1.69 ml/mm Hg x 10, P < 0.001; 8.40 +/- 1.45 vs 10.58 +/- 1.18 ml/mm Hg x 100, P < 0.001 respectively). In parallel, the number of circulating EPCs was significantly reduced in the elderly group compared with the young group (0.13 +/- 0.02 vs 0.17 +/- 0.04%, P < 0.05). The number of circulating EPCs correlated with C(1) large and C(2) small artery elasticity indices (r = 0.47, P < 0.01; r = 0.4, P < 0.01). Fluorescent microscope was used to identify EPCs, which were double positive staining for DiI-acLDL uptake and lectin binding.

CONCLUSION

The present findings suggested that the fall in circulating EPCs with subsequently impaired endothelial-cell repair and function might contribute to reduced arterial elasticity in humans with aging. The decrease in circulating EPCs could serve as a surrogate biologic measure of vascular function and human age.

Pathophysiology of cholangiopathies

The diseases of the intrahepatic biliary tree are a large group of potentially evolutive congenital and acquired liver disorders affecting both the adult and pediatric populations. They represent a relevant cause of liver-related morbidity and mortality and an important indication for liver transplantation, particularly in children. While the practical approach to patients affected by biliary tree diseases has not significantly changed yet, the conceptual approach to the pathophysiology of cholangiopathies has witnessed important advances that will be discussed. The primary cell target of the pathogenetic sequence of these disorders is the biliary epithelium. Cholangiocytes have multifaceted functions, not limited to bile production. Their capability to secrete a range of different pro-inflammatory mediators, cytokines, and chemokines indicates a major role of cholangiocytes in the inflammatory reaction. Furthermore, paracrine secretion of growth factors and peptides mediates an extensive cross-talk with other liver cell types, including hepatocytes, stellate, and endothelial and inflammatory cells. Cholangiopathies share a number of pathogenetic mechanisms, including inflammation, cholestasis, fibrosis, apoptosis, altered development, and neoplastic transformation. These basic disease mechanisms will be discussed in detail, along with the distinct features of a number of cholangiopathies. Furthermore, an increase in the biliary cell compartment is a common response to many forms of liver injury, from cholangiopathies to viral and fulminant hepatitis. Elucidation of these pathophysiologic mechanisms will likely provide clues for future therapeutic strategies. Furthermore, understanding the role of cholangiocytes in liver regeneration/repair and the mechanisms of cholangiocyte activation and their relationship with liver progenitor cell will be of further interest.

Partial serotonergic denervation decreases progenitor cell proliferation in the adult rat hippocampus, but has no effect on rat behavior in the forced swimming test

It has been hypothesized that impaired serotonin (5-HT) neurotransmission contributes to the pathophysiology of depression. Recently, it was shown in adult animals that antidepressants which influence 5-HT levels increase hippocampal progenitor cell proliferation, suggesting an important role of the 5-HT system in the regulation of adult neurogenesis. In this study, we investigated the effects of partial 5-HT denervation of the adult rat forebrain caused by a single para-chloroamphetamine (PCA) administration (10 mg/kg, s.c.) on hippocampal progenitor cell proliferation measured by Ki-67 immunohistochemistry over a 3-week time period. Moreover, behavior of rats was analyzed by using the forced swimming test which serves as a so-called animal model of depression. One week after PCA administration, a significant decrease of Ki-67 immunopositive cells and cell clusters (-25% and -53%, respectively) was found which was recovered over the 3-week period. The decrease in progenitor cell proliferation in the dentate gyrus per animal was positively correlated with the 5-HT denervation. Behavioral analysis of rats revealed no significant differences between vehicle and PCA-treated animals at any of the examined time points. These findings indicate a regulative role of 5-HT for hippocampal progenitor cell proliferation and neurogenesis, but its relation to animal models of depression remains to be elucidated.

Stem cells in medical techonology

Major ethical and scientific debates surround the potential of stem cells to radically alter therapies in health care. This article provides some basic background on the origins and functions of stem cells.

Repopulation of oligodendrocyte progenitor cell depleted tissue in a model of chronic demyelination

Some, but not all chronically demyelinated MS lesions are depleted of oligodendrocyte progenitor cells (OPCs) suggesting that OPCs are destroyed during the process of demyelination and some factor impedes OPC repopulation of the depleted tissue. The chronically demyelinated axons in MS lie in an astrocytic environment and it has been proposed that this might impede entry of OPCs into such regions. By depleting a short length of spinal cord of its OPCs using 40 Gy of X-irradiation in both normal rats and rats with progressive myelin loss accompanied by an astrocytosis (taiep rats), we investigated whether such changes affect the ability of OPCs to repopulate OPC-depleted tissue. In both taiep and normal rats, the rate of repopulation decreases with age, but no difference was detected in the rate at which OPCs repopulated normally myelinated and chronically demyelinated and astrocytosed tissue. This indicates that, if the astrocytic environment of the taiep CNS is comparable to that found in MS lesions, then the presence of chronically demyelinated axons and astrocytosis in chronic MS lesions does not represent a barrier to repopulation of the tissue by OPCs. However, similar to the situation in the normal adult rodent CNS, the rate of repopulation by endogenous OPCs in aged taiep rats is very slow, approximately 0.2 mm per week.

Neural stem cells and their use as therapeutic tool in neurological disorders

Spontaneous neural tissue repair occurs in patients affected by inflammatory and degenerative disorders of the central nervous system (CNS). However, this process is not robust enough to promote a functional and stable recovery of the CNS architecture. The development of cell-based therapies aimed at promoting brain repair, through damaged cell-replacement, is therefore foreseen. Several experimental cell-based strategies aimed at replacing damaged neural cells have been developed in the last 30 years. Although successful in promoting site-specific repair in focal CNS disorders, most of these therapeutic approaches have failed to foster repair in multifocal CNS diseases where the anatomical and functional damage is widespread. Stem cell-based therapies have been recently proposed and might represent in the near future a plausible alternative strategy in these disorders. However, before envisaging any human applications of stem cell-based therapies in neurological diseases, we need to consider some preliminary and still unsolved issues: (i) the ideal stem cell source for transplantation, (ii) the most appropriate route of stem cell administration, and, last but not least, (iii) the best approach to achieve an appropriate, functional, and long-lasting integration of transplanted stem cells into the host tissue.

Effect of cell-density on in-vitro dopaminergic differentiation of mesencephalic precursor cells

Neural precursor cells isolated from early embryonic mesencephalon are in-vitro expanded and differentiated toward dopamine neurons. However, conditions for controlled conversion of the precursors into dopamine neurons largely remained to be determined. We here examined the effects of plating cell density and duration of in-vitro cell expansion on the precursors-derived dopamine differentiation. The yield of dopamine neurons from cultured mesencephalic precursors was greater when the cells were initially plated at higher density. Soluble factors secreted from the precursors appeared to be responsible for the cell density effect. We further demonstrated that the dopamine differentiation potential of the precursors was lost after a long-term cell expansion. Therefore, in order to attain high percentage of dopamine neuron population in mesencephalic precursor cultures, cultures need to be seeded at high cell density and to be expanded for a short period of time.

Paracrine mitogenic effect of human endothelial progenitor cells: role of interleukin-8

Endothelial progenitor cells (EPCs) play an important role in repair of vascular injury and neovascularization. Molecular mechanisms underlying vascular effects of EPCs are not fully understood. The present study was designed to test the hypothesis that human EPCs exert a strong paracrine mitogenic effect on mature endothelial cells. Levels of interleukin-8 (IL-8) were significantly higher in conditioned medium (CM) collected from EPCs than in CM derived from mature endothelial cells [umbilical vein endothelial cells (HUVECs) and coronary artery endothelial cells (CAECs)]. CM of EPCs stimulated proliferation of HUVECs and CAECs. This mitogenic effect was partially inhibited by IL-8-neutralizing antibody. In contrast, CM of HUVECs and CAECs had a weak or no mitogenic effect on mature endothelial cells. Our results demonstrate significantly higher levels of IL-8 secretion by human EPCs than by mature endothelial cells. IL-8 appears to be an important mediator of the paracrine mitogenic effect of EPCs.

Muscle Stem Cells and Exercise Training

Adult skeletal muscle fibers are terminally differentiated such that hypertrophy and regeneration require resident stem cell populations. This review examines the current understanding of the factors regulating muscle stem cells in response to exercise and identify the role of these cells in the adaptive response of skeletal muscle to endurance and resistance exercise training.

Partial enrichment of a population of human limbal epithelial cells with putative stem cell properties based on collagen type IV adhesiveness

The concept that corneal epithelium stem cells reside in limbus has been recognized for more than a decade, but isolation of these stem cells has not been accomplished. This study was an initial attempt to isolate a population of human limbal epithelial cells enriched for certain putative stem cell properties based on their phenotype. Epithelial cells harvested from fresh human limbal rings and their primary cultures were allowed to adhere to collagen IV-coated dishes for 20 min and 2 hr, sequentially. The rapidly adherent cells (RAC), slowly adherent cells and non-adherent cells were evaluated for certain stem cell properties: (a) BrdU-label retention, (b) expression of basal cell (integrin beta1, p63, ABCG2) and differentiation (involucrin, keratin 12) markers, and (c) colony forming efficiency (CFE) and growth capacity on a 3T3 fibroblast feeder layer. Among unfractionated cells and the three selected populations, the RAC, accounting for about 10% of whole population, were enriched 5-fold in BrdU label-retaining cells, displayed the highest number of integrin beta1 and p63 positive and involucrin negative cells, expressed high levels of DeltaNp63 and ABCG2 mRNA, and lacked involucrin and K12 expression, and possessed the greatest CFE and growth capacity. These findings demonstrated for the first time that human limbal epithelial cells with stem cell properties can be partially enriched by their adhesiveness to collagen IV. The RAC population enriched for certain putative stem cell properties may prove useful in the future for transplantation to diseased and damaged corneas with limbal stem cell deficiency.

Unequal segregation of parental chromosomes in embryonic stem cell hybrids

Chromosome segregation was studied in 14 intra- and 20 inter-specific hybrid clones generated by fusion of Mus musculus embryonic stem (ES) cells with fibroblasts or splenocytes of DD/c mice or Mus caroli. As a control for in vitro evolution of tetraploid karyotype we used a set of hybrid clones obtained by fusion of ES cells (D3) with ES cells (TgTP6.3). Identification of the parental chromosomes in the clones was performed by microsatellite analysis and in situ hybridization with labeled species-specific probes. Both analyses have revealed three types of clones: (i) stable tetraploid, observed only for ES x ES cell hybrids; (ii) bilateral loss of chromosomes of both ES and somatic partners; (iii) unilateral segregation of chromosomes of the somatic partner. Observed unilateral segregation was extensive in ES-splenocyte cell hybrids, but lower in ES-fibroblast hybrid clones. Developmental state of the somatic partner is presumably responsible for directional chromosome loss. Nonrandom segregation implies that initial differences in the parental homologous chromosomes were not immediately equalized implying at least transient persistence of the differentiated epigenotype.

The transplantation of neural stem cells and predictive factors in hematopoietic recovery in irradiated mice

A number of surprising observations have shown that stem cells, in suitable conditions, have the ability to produce a whole spectrum of cell types, regardless, whether these tissues are derived from the same germ layer or not. This phenomenon is called stem cell plasticity, which means that tissue-specific stem cells are mutually interchangeable. In our experiments, as a model, we used neural stem cells (NSCs) harvested from fetal (E14-15) neocortex and beta-galactosidase positive. In the first experiment we found that on days 12 and 30 after sub-lethal irradiation (LD 8.5 Gy) and (beta-galactosidase(+)) NSCs transplantation all mice survived, just as the group with bone marrow transplantation. Moreover, the bone marrow of mice transplanted NSCs contained the number of CFU-GM colonies with beta-galactosidase(+) cells which was as much as 50% higher. These differences were statistically significant, p<0.001. In the second experiment, we studied kinetics of (beta-galactosidase(+)) NSCs after their transplantation to sub-lethally irradiated mice. Histochemistry of tissues was performed on days 12 and 30 post-transplantation, and beta-galactosidase(+) cells were detected with the help of histochemical examination of removed tissues (lung, liver, spleen, thymus, and skeletal muscle). In tissues removed on day 12 post-transplantation, we found a significantly higher number of beta-galactosidase(+) cells in the spleen and thymus on day 30. While we presumed the presence beta-galactosidase(+) cells in the spleen, as spleen and reticuloendothelial system represent an important retaining system for different cell types, the presence of beta-galactosidase(+) cells in the thymus was rather surprising but very interesting. This indicates a certain mutual and close interconnection of transplanted stem cells and immune system in an adult organism. In the third experiment, we verified the mutual interchange of Sca-1 surface antigen in the bone marrow cells and NSCs before transplantation. Analysis of this antigen showed 24.8% Sca-1 positive cells among the bone marrow cells, while NSCs were Sca-1 negative. Our experiments show that NSCs share hemopoietic identity and may significantly influence the recovery of damaged hematopoiesis but do not have typical superficial markers as HSCs. This result is important for the determination of predictive factors for hemopoiesis recovery, for stem cell plasticity and for their use in the cell therapy.

Mother-daughter precursor cell fate transformation after Cdc2 down-regulation in the Drosophila bristle lineage

The Drosophila bristle lineage is an excellent system in which to study how cell cycle and fate determination are synchronized in invariant cell lineages. In this model, five different cells arise from a single precursor cell, pI, after four asymmetric cell divisions. Cell diversity is achieved by the asymmetric segregation of cell determinants, such as Numb and Neuralized (Neur), resulting in differential activation of the Notch (N) pathway. We show that down-regulation of Cdc2, by over-expressing Tribbles, Dwee1, and Dmyt1 (three negative regulators of Cdc2) or by using thermo-sensitive Cdc2 mutant flies, delayed pI mitosis, and altered the polarity and the number of subsequent cell divisions. These modifications were associated with a mother-daughter cell fate transformation as the pI cell acquired the identity of the secondary precursor cell, pIIb. This type of change in cell identity only occurred when the N signaling pathway was inactive since ectopic N signaling transformed pI to pIIa-progeny fate. These transformations in cell identity suggest that, although synchronized, cell cycle and fate determination are independent phenomena in the bristle lineage.

Mammary stem cells, self-renewal pathways, and carcinogenesis

The mammary gland epithelial components are thought to arise from stem cells that undergo both self-renewal and differentiation. Self-renewal has been shown to be regulated by the Hedgehog, Notch, and Wnt pathways and the transcription factor B lymphoma Mo-MLV insertion region 1 (Bmi-1). We review data about the existence of stem cells in the mammary gland and the pathways regulating the self-renewal of these cells. We present evidence that deregulation of the self-renewal in stem cells/progenitors might be a key event in mammary carcinogenesis. If 'tumor stem cells' are inherently resistant to current therapies, targeting stem cell self-renewal pathways might provide a novel approach for breast cancer treatment.

History and perspective of stem cell research

Several types of stem cell have been discovered from germ cells, the embryo, fetus and adult. Each of these has promised to revolutionize the future of regenerative medicine through the provision of cell-replacement therapies to treat a variety of debilitating diseases. Stem cell research is politically charged, receives considerable media coverage, raises many ethical and religious debates and generates a great deal of public interest. The tremendous versatility of embryonic stem cells versus the unprecedented reports describing adult stem cell plasticity have ignited debates as to the choice of one cell type over another for future application. However, the biology of these mysterious cells have yet to be understood and a lot more basic research is needed before new therapies using stem-cell-differentiated derivatives can be applied. Stem cell research opens-up the new field of 'cell-based therapies' and, as such, several safety measures have also to be evaluated.

Sequential activation of p75 and TrkB is involved in dendritic development of subventricular zone-derived neuronal progenitors in vitro

Dendritic arbor development of subventricular zone-derived interneurons is a critical step in their integration into functional circuits of the postnatal olfactory bulb. However, the mechanism and molecular control of this process remain unknown. In this study, we have developed a culture model where dendritic development of purified subventricular zone cells proceeds under serum-free conditions in the absence of added growth factors and non-neural cells. We demonstrate that the large majority of these cells in culture express GABA and elaborate dendritic arbors with spine-like protrusions but they do not possess axons. These neurons expressed receptors for neurotrophins including p75, TrkB and TrkC but not TrkA. Application of exogenous neurotrophins, including brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT3) and nerve growth factor (NGF), to cultures stimulated dendritic growth and led to more complex dendritic arbors during the initial 3 days in culture. Our results suggest that these effects are independent of Trk receptors and mediated by the p75/ceramide signaling pathway. We also show that brain-derived neurotrophic factor is the only neurotrophin that is able to influence late-phase dendritic development via TrkB receptor activation. These results suggest that dendritic arbor development of subventricular zone-derived cells may be regulated by neurotrophins through the activation of p75 and the TrkB receptor signaling pathways in a sequentially defined temporal pattern.