Showing papers on "Cellular differentiation published in 2000"
TL;DR: Before the full potential of neural stem cells can be realized, the authors need to learn what controls their proliferation, as well as the various pathways of differentiation available to their daughter cells.
Abstract: Neural stem cells exist not only in the developing mammalian nervous system but also in the adult nervous system of all mammalian organisms, including humans. Neural stem cells can also be derived from more primitive embryonic stem cells. The location of the adult stem cells and the brain regions to which their progeny migrate in order to differentiate remain unresolved, although the number of viable locations is limited in the adult. The mechanisms that regulate endogenous stem cells are poorly understood. Potential uses of stem cells in repair include transplantation to repair missing cells and the activation of endogenous cells to provide "self-repair. " Before the full potential of neural stem cells can be realized, we need to learn what controls their proliferation, as well as the various pathways of differentiation available to their daughter cells.
4,608 citations
TL;DR: A role is established for Oct-3/4 as a master regulator of pluripotency that controls lineage commitment and the sophistication of critical transcriptional regulators is illustrated and the consequent importance of quantitative analyses are illustrated.
Abstract: Cell fate during development is defined by transcription factors that act as molecular switches to activate or repress specific gene expression programmes. The POU transcription factor Oct-3/4 (encoded by Pou5f1) is a candidate regulator in pluripotent and germline cells and is essential for the initial formation of a pluripotent founder cell population in the mammalian embryo. Here we use conditional expression and repression in embryonic stem (ES) cells to determine requirements for Oct-3/4 in the maintenance of developmental potency. Although transcriptional determination has usually been considered as a binary on-off control system, we found that the precise level of Oct-3/4 governs three distinct fates of ES cells. A less than twofold increase in expression causes differentiation into primitive endoderm and mesoderm. In contrast, repression of Oct-3/4 induces loss of pluripotency and dedifferentiation to trophectoderm. Thus a critical amount of Oct-3/4 is required to sustain stem-cell self-renewal, and up- or downregulation induce divergent developmental programmes. Our findings establish a role for Oct-3/4 as a master regulator of pluripotency that controls lineage commitment and illustrate the sophistication of critical transcriptional regulators and the consequent importance of quantitative analyses.
3,745 citations
TL;DR: It is shown that mouse Snail is a strong repressor of transcription of the E-cadherin gene, opening up new avenues for the design of specific anti-invasive drugs.
Abstract: The Snail family of transcription factors has previously been implicated in the differentiation of epithelial cells into mesenchymal cells (epithelial-mesenchymal transitions) during embryonic development. Epithelial-mesenchymal transitions are also determinants of the progression of carcinomas, occurring concomitantly with the cellular acquisition of migratory properties following downregulation of expression of the adhesion protein E-cadherin. Here we show that mouse Snail is a strong repressor of transcription of the E-cadherin gene. Epithelial cells that ectopically express Snail adopt a fibroblastoid phenotype and acquire tumorigenic and invasive properties. Endogenous Snail protein is present in invasive mouse and human carcinoma cell lines and tumours in which E-cadherin expression has been lost. Therefore, the same molecules are used to trigger epithelial-mesenchymal transitions during embryonic development and in tumour progression. Snail may thus be considered as a marker for malignancy, opening up new avenues for the design of specific anti-invasive drugs.
3,426 citations
TL;DR: Adult marrow stromal cells can be induced to overcome their mesenchymal commitment and may constitute an abundant and accessible cellular reservoir for the treatment of a variety of neurologic diseases.
Abstract: Bone marrow stromal cells exhibit multiple traits of a stem cell population. They can be greatly expanded in vitro and induced to differentiate into multiple mesenchymal cell types. However, differentiation to non-mesenchymal fates has not been demonstrated. Here, adult rat stromal cells were expanded as undifferentiated cells in culture for more than 20 passages, indicating their proliferative capacity. A simple treatment protocol induced the stromal cells to exhibit a neuronal phenotype, expressing neuron-specific enolase, NeuN, neurofilament-M, and tau. With an optimal differentiation protocol, almost 80% of the cells expressed NSE and NF-M. The refractile cell bodies extended long processes terminating in typical growth cones and filopodia. The differentiating cells expressed nestin, characteristic of neuronal precursor stem cells, at 5 hr, but the trait was undetectable at 6 days. In contrast, expression of trkA, the nerve growth factor receptor, persisted from 5 hr through 6 days. Clonal cell lines, established from single cells, proliferated, yielding both undifferentiated and neuronal cells. Human marrow stromal cells subjected to this protocol also differentiated into neurons. Consequently, adult marrow stromal cells can be induced to overcome their mesenchymal commitment and may constitute an abundant and accessible cellular reservoir for the treatment of a variety of neurologic diseases.
2,600 citations
TL;DR: The paired box transcription factor Pax7 was isolated by representational difference analysis as a gene specifically expressed in cultured satellite cell-derived myoblasts and it was demonstrated that satellite cells and muscle-derived stem cells represent distinct cell populations.
2,148 citations
1,920 citations
TL;DR: Upon transplantation into brains of immunodeficient neonatal mice, the sorted/expanded hCNS-SC showed potent engraftment, proliferation, migration, and neural differentiation.
Abstract: Stem cells, which are clonogenic cells with self-renewal and multilineage differentiation properties, have the potential to replace or repair damaged tissue. We have directly isolated clonogenic human central nervous system stem cells (hCNS-SC) from fresh human fetal brain tissue, using antibodies to cell surface markers and fluorescence-activated cell sorting. These hCNS-SC are phenotypically 5F3 (CD133)+, 5E12+, CD34−, CD45−, and CD24−/lo. Single CD133+ CD34− CD45− sorted cells initiated neurosphere cultures, and the progeny of clonogenic cells could differentiate into both neurons and glial cells. Single cells from neurosphere cultures initiated from CD133+ CD34− CD45− cells were again replated as single cells and were able to reestablish neurosphere cultures, demonstrating the self-renewal potential of this highly enriched population. Upon transplantation into brains of immunodeficient neonatal mice, the sorted/expanded hCNS-SC showed potent engraftment, proliferation, migration, and neural differentiation.
1,919 citations
TL;DR: It is shown that, in a strain of mice incapable of developing cells of the myeloid and lymphoid lineages, transplanted adult bone marrow cells migrated into the brain and differentiated into cells that expressed neuron-specific antigens.
Abstract: Bone marrow stem cells give rise to a variety of hematopoietic lineages and repopulate the blood throughout adult life. We show that, in a strain of mice incapable of developing cells of the myeloid and lymphoid lineages, transplanted adult bone marrow cells migrated into the brain and differentiated into cells that expressed neuron-specific antigens. These findings raise the possibility that bone marrow-derived cells may provide an alternative source of neurons in patients with neurodegenerative diseases or central nervous system injury.
1,887 citations
TL;DR: Both intrinsic and extrinsic signals regulate stem cell fate and some of these signals have now been identified and can be exploited in the application of stem cells to tissue replacement therapy.
Abstract: Stem cells are currently in the news for two reasons: the successful cultivation of human embryonic stem cell lines and reports that adult stem cells can differentiate into developmentally unrelated cell types, such as nerve cells into blood cells Both intrinsic and extrinsic signals regulate stem cell fate and some of these signals have now been identified Certain aspects of the stem cell microenvironment, or niche, are conserved between tissues, and this can be exploited in the application of stem cells to tissue replacement therapy
1,798 citations
TL;DR: A cell labeling approach using short HIV-Tat peptides to derivatize superparamagnetic nanoparticles is developed, which efficiently internalized into hematopoietic and neural progenitor cells in quantities up to 10–30 pg of super paramagnetic iron per cell.
Abstract: The ability to track the distribution and differentiation of progenitor and stem cells by high-resolution in vivo imaging techniques would have significant clinical and research implications We have developed a cell labeling approach using short HIV-Tat peptides to derivatize superparamagnetic nanoparticles The particles are efficiently internalized into hematopoietic and neural progenitor cells in quantities up to 10-30 pg of superparamagnetic iron per cell Iron incorporation did not affect cell viability, differentiation, or proliferation of CD34+ cells Following intravenous injection into immunodeficient mice, 4% of magnetically CD34+ cells homed to bone marrow per gram of tissue, and single cells could be detected by magnetic resonance (MR) imaging in tissue samples In addition, magnetically labeled cells that had homed to bone marrow could be recovered by magnetic separation columns Localization and retrieval of cell populations in vivo enable detailed analysis of specific stem cell and organ interactions critical for advancing the therapeutic use of stem cells
1,788 citations
TL;DR: The generation of neuronal phenotypes in the adult brain 1 to 6 months after an adult bone marrow transplant demonstrates a remarkable plasticity of adult tissues with potential clinical applications.
Abstract: After intravascular delivery of genetically marked adult mouse bone marrow into lethally irradiated normal adult hosts, donor-derived cells expressing neuronal proteins (neuronal phenotypes) developed in the central nervous system. Flow cytometry revealed a population of donor-derived cells in the brain with characteristics distinct from bone marrow. Confocal microscopy of individual cells showed that hundreds of marrow-derived cells in brain sections expressed gene products typical of neurons (NeuN, 200-kilodalton neurofilament, and class III beta-tubulin) and were able to activate the transcription factor cAMP response element-binding protein (CREB). The generation of neuronal phenotypes in the adult brain 1 to 6 months after an adult bone marrow transplant demonstrates a remarkable plasticity of adult tissues with potential clinical applications.
TL;DR: It is demonstrated that human and mouse BMSC can be induced to differentiate into neural cells under experimental cell culture conditions.
TL;DR: The authors showed that Wnt signaling maintains preadipocytes in an undifferentiated state through inhibition of the adipogenic transcription factors CCAAT/enhancer binding protein alpha (C/EBPalpha) and peroxisome proliferator activated receptor gamma (PPARgamma).
Abstract: Wnts are secreted signaling proteins that regulate developmental processes. Here we show that Wnt signaling, likely mediated by Wnt-10b, is a molecular switch that governs adipogenesis. Wnt signaling maintains preadipocytes in an undifferentiated state through inhibition of the adipogenic transcription factors CCAAT/enhancer binding protein alpha (C/EBPalpha) and peroxisome proliferator- activated receptor gamma (PPARgamma). When Wnt signaling in preadipocytes is prevented by overexpression of Axin or dominant-negative TCF4, these cells differentiate into adipocytes. Disruption of Wnt signaling also causes transdifferentiation of myoblasts into adipocytes in vitro, highlighting the importance of this pathway not only in adipocyte differentiation but also in mesodermal cell fate determination.
TL;DR: The characteristics of the major components of the p38 signalling transduction pathway are summarized and the targets of this pathway are highlighted and the physiological function ofThe p38 activation is highlighted.
TL;DR: The ability to induce formation of human embryoid bodies that contain cells of neuronal, hematopoietic and cardiac origins will be useful in studying early human embryonic development as well as in transplantation medicine.
Abstract: Embryonic stem (ES) cells are lines of cells that are isolated from blastocysts. The murine ES cells were demonstrated to be true pluripotent cells as they differentiate into all embryonic lineages. Yet, in vitro differentiation of rhesus ES cells was somewhat inconsistent and disorganized. The recent isolation of human ES cells calls for exploring their pluripotential nature. Human ES cells were grown in suspension to induce their differentiation into embryoid bodies (EBs). The differentiation status of the human ES cells and EBs was analyzed by following the expression pattern of several lineage-specific molecular markers using reverse transcription polymerase chain reaction (RT-PCR) and in situ hybridization. Here we report the induction in vitro of cystic embryoid bodies from human ES cells. Our findings demonstrate induction of expression of cell-specific genes during differentiation of the human ES cells into EBs. In the human EBs, we could show a characteristic regional expression of embryonic markers specific to different cellular lineages, namely, ζ-globin (mesoderm), neurofilament 68Kd (ectoderm), and α-fetoprotein (endoderm). Moreover, we present a synchronously pulsing embryoid body that expresses the myocardium marker α-cardiac actin. In addition, dissociating the embryoid bodies and plating the cells as monolayers results in multiple morphologies, among them cells with neuronal appearance that express neurofilament 68Kd chain. Human ES cells can reproducibly differentiate in vitro into EBs comprising the three embryonic germ layers. The ability to induce formation of human embryoid bodies that contain cells of neuronal, hematopoietic and cardiac origins will be useful in studying early human embryonic development as well as in transplantation medicine.
TL;DR: A method for obtaining dopaminergic (DA) and serotonergic neurons in high yield from mouse ES cells in vitro is presented and it is demonstrated that the ES cells can be obtained in unlimited numbers and that these neuron types are generated efficiently.
Abstract: Embryonic stem (ES) cells are clonal cell lines derived from the inner cell mass of the developing blastocyst that can proliferate extensively in vitro and are capable of adopting all the cell fates in a developing embryo. Clinical interest in the use of ES cells has been stimulated by studies showing that isolated human cells with ES properties from the inner cell mass or developing germ cells can provide a source of somatic precursors. Previous studies have defined in vitro conditions for promoting the development of specific somatic fates, specifically, hematopoietic, mesodermal, and neurectodermal. In this study, we present a method for obtaining dopaminergic (DA) and serotonergic neurons in high yield from mouse ES cells in vitro. Furthermore, we demonstrate that the ES cells can be obtained in unlimited numbers and that these neuron types are generated efficiently. We generated CNS progenitor populations from ES cells, expanded these cells and promoted their differentiation into dopaminergic and serotonergic neurons in the presence of mitogen and specific signaling molecules. The differentiation and maturation of neuronal cells was completed after mitogen withdrawal from the growth medium. This experimental system provides a powerful tool for analyzing the molecular mechanisms controlling the functions of these neurons in vitro and in vivo, and potentially for understanding and treating neurodegenerative and psychiatric diseases.
TL;DR: This analysis sets the stage for directing differentiation of human ES cells in culture and indicates that multiple human cell types may be enriched in vitro by specific factors.
Abstract: Human embryonic stem (ES) cells are pluripotent cells derived from the inner cell mass of in vitro fertilized human blastocysts. We examined the potential of eight growth factors [basic fibroblast growth factor (bFGF), transforming growth factor beta1 (TGF-beta1), activin-A, bone morphogenic protein 4 (BMP-4), hepatocyte growth factor (HGF), epidermal growth factor (EGF), beta nerve growth factor (betaNGF), and retinoic acid] to direct the differentiation of human ES-derived cells in vitro. We show that human ES cells that have initiated development as aggregates (embryoid bodies) express a receptor for each of these factors, and that their effects are evident by differentiation into cells with different epithelial or mesenchymal morphologies. Differentiation of the cells was assayed by expression of 24 cell-specific molecular markers that cover all embryonic germ layers and 11 different tissues. Each growth factor has a unique effect that may result from directed differentiation and/or cell selection, and we can divide the overall effects of the factors into three categories: growth factors (Activin-A and TGFbeta1) that mainly induce mesodermal cells; factors (retinoic acid, EGF, BMP-4, and bFGF) that activate ectodermal and mesodermal markers; and factors (NGF and HGF) that allow differentiation into the three embryonic germ layers, including endoderm. None of the growth factors directs differentiation exclusively to one cell type. This analysis sets the stage for directing differentiation of human ES cells in culture and indicates that multiple human cell types may be enriched in vitro by specific factors.
TL;DR: Transgenic loss-of-function and overexpression models show that the dosage of glial cell line-derived neurotrophic factor (GDNF), produced by Sertoli cells, regulates cell fate decisions of undifferentiated sperMatogonial cells that include the stem cells for spermatogenesis.
Abstract: The molecular control of self-renewal and differentiation of stem cells has remained enigmatic. Transgenic loss-of-function and overexpression models now show that the dosage of glial cell line-derived neurotrophic factor (GDNF), produced by Sertoli cells, regulates cell fate decisions of undifferentiated spermatogonial cells that include the stem cells for spermatogenesis. Gene-targeted mice with one GDNF-null allele show depletion of stem cell reserves, whereas mice overexpressing GDNF show accumulation of undifferentiated spermatogonia. They are unable to respond properly to differentiation signals and undergo apoptosis upon retinoic acid treatment. Nonmetastatic testicular tumors are regularly formed in older GDNF-overexpressing mice. Thus, GDNF contributes to paracrine regulation of spermatogonial self-renewal and differentiation.
TL;DR: The matrix metalloproteinase MMP-9/gelatinase B is upregulated in angiogenic dysplasias and invasive cancers of the epidermis in a mouse model of multi-stage tumorigenesis elicited by HPV16 oncogenes, suggesting inflammatory cells can be coconspirators in carcinogenesis.
TL;DR: Neural induction by SDIA provides a new powerful tool for both basic neuroscience research and therapeutic applications.
TL;DR: The laminins are a family of glycoproteins that provide an integral part of the structural scaffolding of basement membranes in almost every animal tissue and have unique and shared cell interactions mediated by integrins, dystroglycan, and other receptors.
Abstract: The laminins are a family of glycoproteins that provide an integral part of the structural scaffolding of basement membranes in almost every animal tissue. Each laminin is a heterotrimer assembled from alpha, beta, and gamma chain subunits, secreted and incorporated into cell-associated extracellular matrices. The laminins can self-assemble, bind to other matrix macromolecules, and have unique and shared cell interactions mediated by integrins, dystroglycan, and other receptors. Through these interactions, laminins critically contribute to cell differentiation, cell shape and movement, maintenance of tissue phenotypes, and promotion of tissue survival. Recent advances in the characterization of genetic disruptions in humans, mice, nematodes and flies have revealed developmental roles for the different laminin subunits in diverse cell types, affecting differentiation from blastocyst formation to the post-natal period. These genetic defects have challenged some of the previous concepts about basement membranes and have shed new light on the diversity and complexity of laminin functions as well as established the molecular basis of several human diseases.
TL;DR: The working hypothesis is that inhibition of HDAC activity leads to the modulation of expression of a specific set of genes that, in turn, result in growth arrest, differentiation, and/or apoptotic cell death.
Abstract: Histone deacetylase (HDAC) inhibitors have been shown to be potent inducers of growth arrest, differentiation, and/or apoptotic cell death of transformed cells in vitro and in vivo. One class of HDAC inhibitors, hydroxamic acid-based hybrid polar compounds (HPCs), induce differentiation at micromolar or lower concentrations. Studies (x-ray crystallographic) showed that the catalytic site of HDAC has a tubular structure with a zinc atom at its base and that these HDAC inhibitors, such as suberoylanilide hydroxamic acid and trichostatin A, fit into this structure with the hydroxamic moiety of the inhibitor binding to the zinc. HDAC inhibitors cause acetylated histones to accumulate in both tumor and normal tissues, and this accumulation can be used as a marker of the biologic activity of the HDAC inhibitors. Hydroxamic acid-based HPCs act selectively to inhibit tumor cell growth at levels that have little or no toxicity for normal cells. These compounds also act selectively on gene expression, altering the expression of only about 2% of the genes expressed in cultured tumor cells. In general, chromatin fractions enriched in actively transcribed genes are also enriched in highly acetylated core histones, whereas silent genes are associated with nucleosomes with a low level of acetylation. However, HDACs can also acetylate proteins other than histones in nucleosomes. The role that these other targets play in the induction of cell growth arrest, differentiation, and/or apoptotic cell death has not been determined. Our working hypothesis is that inhibition of HDAC activity leads to the modulation of expression of a specific set of genes that, in turn, result in growth arrest, differentiation, and/or apoptotic cell death. The hydroxamic acid-based HPCs are potentially effective agents for cancer therapy and, possibly, cancer chemoprevention.
TL;DR: It is shown that dendritic cells (DCs) are major targets of 1,25(OH)2D3-induced immunosuppressive activity, associated with a reduced capacity of DCs to activate alloreactive T cells, as determined by decreased proliferation and IFN-γ secretion in mixed leukocyte cultures.
Abstract: 1 Alpha,25-dihydroxyvitamin D3 (1,25(OH)2D3), the active form of vitamin D3, is a potent immunomodulatory agent. Here we show that dendritic cells (DCs) are major targets of 1,25(OH)2D3-induced immunosuppressive activity. 1,25(OH)2D3 prevents the differentiation in immature DCs of human monocytes cultured with GM-CSF and IL-4. Addition of 1,25(OH)2D3 during LPS-induced maturation maintains the immature DC phenotype characterized by high mannose receptor and low CD83 expression and markedly inhibits up-regulation of the costimulatory molecules CD40, CD80, and CD86 and of class II MHC molecules. This is associated with a reduced capacity of DCs to activate alloreactive T cells, as determined by decreased proliferation and IFN-gamma secretion in mixed leukocyte cultures. 1, 25(OH)2D3 also affects maturing DCs, leading to inhibition of IL-12p75 and enhanced IL-10 secretion upon activation by CD40 ligation. In addition, 1,25(OH)2D3 promotes the spontaneous apoptosis of mature DCs. The modulation of phenotype and function of DCs matured in the presence of 1,25(OH)2D3 induces cocultured alloreactive CD4+ cells to secrete less IFN-gamma upon restimulation, up-regulate CD152, and down-regulate CD154 molecules. The inhibition of DC differentiation and maturation as well as modulation of their activation and survival leading to T cell hyporesponsiveness may explain the immunosuppressive activity of 1, 25(OH)2D3.
TL;DR: It is shown that mice deficient in Hes1 (encoding Hes-1) display severe pancreatic hypoplasia caused by depletion of pancreatic epithelial precursors due to accelerated differentiation of post-mitotic endocrine cells expressing glucagon, and upregulation of several bHLH components is associated with precocious and excessive differentiation of multiple endocrine cell types in the developing stomach and gut, showing that Hes- 1 operates as a general negative regulator of endodermal endocrine differentiation.
Abstract: Development of endocrine cells in the endoderm involves Atonal and Achaete/Scute-related basic helix-loop-helix (bHLH) proteins. These proteins also serve as neuronal determination and differentiation factors, and are antagonized by the Notch pathway partly acting through Hairy and Enhancer-of-split (HES)-type proteins. Here we show that mice deficient in Hes1 (encoding Hes-1) display severe pancreatic hypoplasia caused by depletion of pancreatic epithelial precursors due to accelerated differentiation of post-mitotic endocrine cells expressing glucagon. Moreover, upregulation of several bHLH components is associated with precocious and excessive differentiation of multiple endocrine cell types in the developing stomach and gut, showing that Hes-1 operates as a general negative regulator of endodermal endocrine differentiation.
TL;DR: Since the IL-6/gp130/STAT3 signaling pathway is involved in both B cell growth and differentiation into plasma cells it is likely to play a central role in the generation of plasma cell neoplasias.
Abstract: Members of the IL-6 cytokine family are involved in a variety of biological responses, including the immune response, inflammation, hematopoiesis, and oncogenesis by regulating cell growth, survival, and differentiation. These cytokines use gp130 as a common receptor subunit. The binding of ligand to gp130 activates the JAK/STAT signal transduction pathway, where STAT3 plays a central role in transmitting the signals from the membrane to the nucleus. STAT3 is essential for gp130-mediated cell survival and G1 to S cell-cycle-transition signals. Both c-myc and pim have been identified as target genes of STAT3 and together can compensate for STAT3 in cell survival and cell-cycle transition. STAT3 is also required for gp130-mediated maintenance of the pluripotential state of proliferating embryonic stem cells and for the gp130-induced macrophage differentiation of M1 cells. Furthermore, STAT3 regulates cell movement, such as leukocyte, epidermal cell, and keratinocyte migration. STAT3 also appears to regulate B cell differentiation into antibody-forming plasma cells. Since the IL-6/gp130/STAT3 signaling pathway is involved in both B cell growth and differentiation into plasma cells it is likely to play a central role in the generation of plasma cell neoplasias.
TL;DR: It is shown that neural stem cells from the adult mouse brain can contribute to the formation of chimeric chick and mouse embryos and give rise to cells of all germ layers, demonstrating that an adult neural stem cell has a very broad developmental capacity.
Abstract: The differentiation potential of stem cells in tissues of the adult has been thought to be limited to cell lineages present in the organ from which they were derived, but there is evidence that some stem cells may have a broader differentiation repertoire. We show here that neural stem cells from the adult mouse brain can contribute to the formation of chimeric chick and mouse embryos and give rise to cells of all germ layers. This demonstrates that an adult neural stem cell has a very broad developmental capacity and may potentially be used to generate a variety of cell types for transplantation in different diseases.
TL;DR: A regulatory loop, which involves the hormone leptin, may help to explain the protective effect of obesity on bone mass in humans and provide a novel physiologic concept that may shed light on the etiology of osteoporosis and help to identify new therapeutic targets.
Abstract: The study of the biology of osteoblasts, or bone-forming cells, illustrates how mammalian genetics has profoundly modified our understanding of cell differentiation and physiologic processes. Indeed, genetic-based studies over the past 5 years have revealed how osteoblast differentiation is controlled through growth and transcription factors. Likewise, the recent identification, using mutant mouse models, of a central component in the regulation of bone formation expands our understanding of the control of bone remodeling. This regulatory loop, which involves the hormone leptin, may help to explain the protective effect of obesity on bone mass in humans. In addition, it provides a novel physiologic concept that may shed light on the etiology of osteoporosis and help to identify new therapeutic targets.
TL;DR: Adult retinal stem cells are localized to the pigmented ciliary margin and not to the central and peripheral retinal pigmented epithelium, indicating that these cells may be homologous to those found in the eye germinal zone of other nonmammalian vertebrates.
Abstract: The mature mammalian retina is thought to lack regenerative capacity. Here, we report the identification of a stem cell in the adult mouse eye, which represents a possible substrate for retinal regeneration. Single pigmented ciliary margin cells clonally proliferate in vitro to form sphere colonies of cells that can differentiate into retinal-specific cell types, including rod photoreceptors, bipolar neurons, and Muller glia. Adult retinal stem cells are localized to the pigmented ciliary margin and not to the central and peripheral retinal pigmented epithelium, indicating that these cells may be homologous to those found in the eye germinal zone of other nonmammalian vertebrates.
TL;DR: Duct tissue from human pancreas can be expanded in culture and then be directed to differentiate into glucose responsive islet tissue in vitro, which may provide a potential new source of pancreatic islet cells for transplantation.
Abstract: A major obstacle to successful islet transplantation for both type 1 and 2 diabetes is an inadequate supply of insulin-producing tissue. This need for transplantable human islets has stimulated efforts to expand existing pancreatic islets and/or grow new ones. To test the hypothesis that human adult duct tissue could be expanded and differentiated in vitro to form islet cells, digested pancreatic tissue that is normally discarded from eight human islet isolations was cultured under conditions that allowed expansion of the ductal cells as a monolayer whereupon the cells were overlaid with a thin layer of Matrigel. With this manipulation, the monolayer of epithelial cells formed three-dimensional structures of ductal cysts from which 50-to 150-μm diameter islet-like clusters of pancreatic endocrine cells budded. Over 3–4 weeks culture the insulin content per flask increased 10- to 15-fold as the DNA content increased up to 7-fold. The cultivated human islet buds were shown by immunofluorescence to consist of cytokeratin 19-positive duct cells and hormone-positive islet cells. Double staining of insulin and non-β cell hormones in occasional cells indicated immature cells still in the process of differentiation. Insulin secretion studies were done over 24 h in culture. Compared with their basal secretion at 5 mM glucose, cysts/cultivated human islet buds exposed to stimulatory 20 mM glucose had a 2.3-fold increase in secreted insulin. Thus, duct tissue from human pancreas can be expanded in culture and then be directed to differentiate into glucose responsive islet tissue in vitro. This approach may provide a potential new source of pancreatic islet cells for transplantation.
TL;DR: The most primitive neurotrophin genes have been isolated from jawless fishes, a river lamprey and the Atlantic hagfish, and they encode pre-pro-neurotrophins, which may serve the purpose of limiting their range of action.
Abstract: Neurons are specialized cells with a complex morphology that represent the functional unit of the nervous system. They are generated in remarkable numbers, particularly in higher vertebrates. In the human brain, for example, there may be ∼85 billion neurons (Williams and Herrup 1988). There is little cell division in the adult nervous system of vertebrates, and in most areas, the final number of neurons is determined early in development, at about the time when neurons extend axons (Oppenheim 1991). Neuronal numbers are controlled both by cell-intrinsic and cell-extrinsic programs. Cell-intrinsic programs govern basic aspects of neuronal differentiation in vertebrates, and a number of transcription factors have been shown to be expressed in well-defined areas of the nervous system (for review, see Rubenstein et al. 1998). Cell-extrinsic mechanisms play a prominent role in vertebrates. They involve the secretion of diffusible molecules controlling the survival of neurons produced in excess early in development, a process thought to help match the size of neuronal populations with the territory they innervate (Purves 1988; Oppenheim 1991). However, much of the developmental growth of the animal must still take place by the time these numerical adjustments are completed (Purves 1988). The neurons that have escaped elimination grow proportionally with the organism, enlarging their size by adding dendrites that grow out from the cell bodies. Secreted proteins play a crucial role in the control of neuronal numbers and of dendritic growth. The best studied group is a family of structurally related molecules termed neurotrophins (Barde 1990). The first neurotrophin identified was originally designated “the” nerve growth factor (NGF; Levi-Montalcini 1966). However, only very few neurons were found to be NGF responsive in the central nervous system (CNS), and the isolation of brain-derived neurotrophic factor (BDNF) from the brain helped establish the concept that the fate and the shape of most vertebrate neurons can be regulated by diffusible growth factors (Hofer and Barde 1988). In the context of the regulation of neuronal shape, a particularly attractive and important feature of the neurotrophins is that they are synthesized and released by neurons and that both their biosynthesis and secretion depend on neuronal activity (Thoenen 1995). In addition to ngf and bdnf, two other neurotrophin genes have been identified in mammals, neurotrophin-3 (nt3) and neurotrophin-4/5 (nt4/5). These four genes encode pre-pro-neurotrophins. The processed proteins have a size of ∼13,000 D, and they exist in solution as noncovalently linked homodimers (for review, see Barde 1990; Ibanez 1998). They all have very basic isoelectric points, a somewhat unusual property for secreted proteins, which may serve the purpose of limiting their range of action. The structural hallmark of the protomer is a characteristic arrangement of the disulfide bridges known as the cystine knot (McDonald et al. 1991), later identified in other secreted proteins such as the plateletderived growth factors and the transforming growth factor– s (TGFs; McDonald and Hendrickson 1993). With the exception of NT4/5, neurotrophin sequences are highly conserved in mammals. In bony fishes, more neurotrophin and receptor genes have been isolated than in mammals (for review, see Hallbook 1999). Based on sequence comparisons and on the isolation of neurotrophin genes in various vertebrates, it is thought that ngf/nt3 and bdnf/nt4/5 evolved from separate duplication events (Hallbook 1999). The most primitive neurotrophin genes have been isolated from jawless fishes, a river lamprey and the Atlantic hagfish. The jawless fish lineage diverged about 460 million years ago in vertebrate history, and the neurotrophin receptors of the trk family (see below) seem to have coevolved with the neurotrophin genes (Hallbook, 1999). So far, no neurotrophin-like sequences have been detected in invertebrates typically used by geneticists, and unlike other growth factors such as members of the Wnt, fibroblast growth factor or TGFfamilies, genes coding for neurotrophins and their receptors have not been identified in the genome of the nematode Caenorhabditis elegans (Bargmann 1998). Clearly then, a nervous system can be put together in the absence of neurotrophins, including precise wiring, chemical neurotransmission, and the 1Corresponding author. E-MAIL yves.barde@neuro.mpg.de; FAX 49-89-8578-3749. Article and publication are at www.genesdev.org/cgi/doi/10.1101/ gad.841400.