RESUMEN
Well-characterized animal models that mimic the human response to potentially lethal doses of radiation are required to assess the efficacy of medical countermeasures under the criteria of the US Food and Drug Administration's Animal Rule. Development of a model for the gastrointestinal acute radiation syndrome requires knowledge of the radiation dose-response relationship and time course of mortality and morbidity across the acute and prolonged gastrointestinal radiation syndrome. The nonhuman primate, rhesus macaque, is a relevant animal model that has been used to determine the efficacy of medical countermeasures to mitigate major signs of morbidity and mortality relative to the hematopoietic acute radiation syndrome, gastrointestinal acute radiation syndrome, and lung injury. It can be used to assess the natural history of gastrointestinal damage, concurrent multiple organ injury, and aspects of the mechanism of action for acute radiation exposure and treatment. A systematic review of relevant studies that determined the dose-response relationship for the gastrointestinal acute and prolonged radiation syndrome in the rhesus macaque relative to radiation dose, quality, dose rate, exposure uniformity, and use of medical management has never been performed.
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Síndrome de Radiación Aguda/etiología , Enfermedades Gastrointestinales/etiología , Síndrome de Radiación Aguda/patología , Síndrome de Radiación Aguda/terapia , Animales , Relación Dosis-Respuesta en la Radiación , Enfermedades Gastrointestinales/patología , Enfermedades Gastrointestinales/terapia , Tracto Gastrointestinal/patología , Tracto Gastrointestinal/efectos de la radiación , Macaca mulattaRESUMEN
OBJECTIVE: To analyse the structural and kinetic response of small intestinal crypt epithelial cells including stem cells to highly active antiretroviral therapy (HAART). DESIGN: Crypt size and proliferative activity of transit and stem cells in jejunal mucosa were quantified using morphometric techniques. METHODS: Crypt length was measured by counting the number of enterocytes along one side of a number of crypts in each biopsy specimen and the mean crypt length was calculated. Proliferating crypt cells were identified with MIB-1 monoclonal antibody, and the percentage of crypt cells in proliferation was calculated at each cell position along the length of the crypt (proliferation index). Data were obtained from 9 HIV-positive test patients co-infected with microsporidia, 34 HIV-positive patients receiving HAART and 13 control cases. RESULTS: Crypt length was significantly greater in test patients than in controls, but crypt length in patients receiving HAART was normal. The proliferation index was greater in test subjects than in controls in stem and transit cell compartments, and was decreased in patients treated with HAART only in the stem cell region of the crypt. CONCLUSIONS: Villous atrophy in HIV enteropathy is attributed to crypt hypertrophy and encroachment of crypt cells onto villi. HAART restores normal crypt structure by inhibition of HIV-driven stem cell hyperproliferation at the crypt bases.
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Terapia Antirretroviral Altamente Activa , Proliferación Celular/efectos de los fármacos , Enteropatía por VIH/patología , Mucosa Intestinal/patología , Células Madre/efectos de los fármacos , Enteropatía por VIH/tratamiento farmacológico , Humanos , Hipertrofia/patología , Mucosa Intestinal/efectos de los fármacos , Yeyuno/efectos de los fármacos , Yeyuno/patología , Índice Mitótico , Células Madre/patologíaRESUMEN
Stem cells have been identified in two locations in small intestinal crypts; those intercalated between Paneth cells and another population (which retains DNA label) are located above the Paneth cell zone, at cell position 4. Because of disadvantages associated with the use of DNA label, doxycycline-induced transient transgenic expression of histone 2B (H2B)-green fluorescent protein (GFP) was investigated. H2B-GFP-retaining putative stem cells were consistently seen, with a peak at cell position 4, over chase periods of up to 112 days. After a 28-day chase, a subpopulation of the H2B-GFP-retaining cells was cycling, but the slow cycling status of the majority was illustrated by lack of expression of pHistone H3 and Ki67. Although some H2B-GFP-retaining cells were sensitive to low-dose radiation, the majority was resistant to low- and high-dose radiation-induced cell death, and a proportion of the surviving cells proliferated during subsequent epithelial regeneration. Long-term retention of H2B-GFP in a subpopulation of small intestinal Paneth cells was also seen, implying that they are long lived. In contrast to the small intestine, H2B-GFP-retaining epithelial cells were not seen in the colon from 28-day chase onward. This implies important differences in stem cell function between these two regions of the gastrointestinal tract, which may have implications for region-specific susceptibility to diseases (such as cancer and ulcerative colitis), in which epithelial stem cells and their progeny are involved.
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Colon/citología , Histonas , Intestino Delgado/citología , Células de Paneth/metabolismo , Proteínas Recombinantes de Fusión , Células Madre/citología , Animales , Proliferación Celular , ADN/metabolismo , Proteínas Fluorescentes Verdes/metabolismo , Intestino Delgado/efectos de la radiación , Ratones , Células Madre/metabolismo , Células Madre/efectos de la radiaciónRESUMEN
PURPOSE: The intestinal epithelium has a high rate of cell turnover, which is regulated by stem cells located near the base of crypts. We aimed to investigate stem cell-dependent characteristics of cell proliferation, apoptosis, and crypt size in terminal ileum and different regions of the colon. METHODS AND MATERIALS: Mice were studied under steady-state conditions and after radiation-induced stem cell apoptosis. Percentage of proliferating or apoptotic cells at a particular cell position (cp) along the crypt axis was expressed as labeling or apoptotic index. RESULTS: Under steady-state conditions: crypt size was smallest in the ascending colon. In contrast to other regions of the colon, the distribution profile of proliferating cells in ascending colon showed some similarity to that in the terminal ileum. Postirradiation: apoptotic cells were prominent at the bottom of the crypt of mid- and descending colon but in the ascending colon, they were seen with similar frequency from cp 1 to 4. During regeneration, a constant proliferative capacity was seen above Paneth cells in the terminal ileum. In the ascending (but not mid- or descending) colon, the profile of proliferating cells over the first 4 days after irradiation showed a similarity to that in the terminal ileum. CONCLUSIONS: Profiles of proliferating epithelial cells (under steady-state conditions and postirradiation) and apoptotic cells (postirradiation) suggest similarities in the location of stem cells in the ascending colon and terminal ileum.
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Apoptosis/efectos de la radiación , Proliferación Celular/efectos de la radiación , Colon/efectos de la radiación , Íleon/efectos de la radiación , Células Madre/efectos de la radiación , Animales , Movimiento Celular/fisiología , Movimiento Celular/efectos de la radiación , Colon/citología , Colon/fisiología , Femenino , Íleon/citología , Íleon/fisiología , Ratones , Células de Paneth/fisiología , Dosis de Radiación , Regeneración/fisiología , Células Madre/fisiologíaRESUMEN
Adult stem cells in rapidly renewing tissues have been classically defined as rare, relatively quiescent cells with the unique capacity to constantly self-renew and regenerate tissues during homeostasis. Although this view remains firmly embedded in the skin field, particularly in the area of hair follicle stem cell biology, it has been challenged by a number of notable publications in 2007. These papers leave an uncomfortable feeling with the reader if one believes that stem cells and transit amplifying cells are two polar opposites and 'never the twain shall meet.' Even if you do not subscribe to this extreme view, the implications appear to be far-reaching given that the majority of techniques devised for stem cell identification have used the fundamental tenet that the proliferating compartment is comprised of two distinct, mutually exclusive compartments, i.e. a minor proportion of long-lived quiescent stem cells with unlimited self-renewal and a large pool of rapidly cycling, short-lived transient amplifying cells with limited or no self-renewal capacity in normal steady-state conditions. However, these recent findings have resulted in papers that could be described as sensationalistic because they make little or no attempt to reconcile their observations with the large bulk of historical data with direct bearing on the interpretation of stem cell activity in normal steady-state conditions. Here, we offer some explanations that may help to integrate all of the data while presenting a case that both quiescent stem cells and cycling 'transit amplifying' cells contribute to epidermal replacement.
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Células Madre Adultas/citología , Folículo Piloso/citología , Animales , Ciclo Celular , Proliferación Celular , Humanos , Modelos Biológicos , Proyectos de InvestigaciónRESUMEN
OBJECTIVES: The study aim was to analyse the kinetics of stem and transit cells in the crypts of jejunal mucosa infected with HIV and Microsporidia. DESIGN: The size of villi, depth of crypts and proliferative activity of transit and stem cells in jejunal mucosa were measured using morphometric techniques. METHODS: The surface area/volume ratio (S/V) of jejunal biopsies was estimated under light microscopy using a Weibel graticule. Crypt length was measured by counting enterocytes along the crypt side from the base to the villus junction, and the mean crypt length was calculated. The S/V and crypt lengths of the jejunal mucosa of 21 HIV and Microsporidia-infected test cases were compared with 14 control cases. The labelling index in relation to the crypt cell position of 10 of the test cases was analysed compared with 13 control cases. RESULTS: Differences were found in the S/V and crypt length, and there was a negative correlation between S/V and crypt length in test and control cases combined. Cell labelling indices fell into low and high proliferation groups. There were significant differences in labelling indices between low proliferation test cases and controls, between high proliferation test cases and controls, and between high and low proliferation test cases. CONCLUSION: Villous atrophy induced by HIV and Microsporidia is attributed to crypt cell hyperplasia and the encroachment of crypt cells onto villi. These infections induce crypt hypertrophy by stimulating cell mitosis predominantly in transit cells but also in stem cells. Increased stem cell proliferation occurs only in high proliferation cases.
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Infecciones Oportunistas Relacionadas con el SIDA/patología , Enteropatía por VIH/patología , Mucosa Intestinal/patología , Yeyuno/patología , Microsporidiosis/patología , Infecciones Oportunistas Relacionadas con el SIDA/complicaciones , Adulto , Atrofia/microbiología , Atrofia/patología , Biopsia , Recuento de Células , Proliferación Celular , Femenino , Enteropatía por VIH/complicaciones , Humanos , Masculino , Microsporidiosis/complicaciones , Persona de Mediana Edad , Células de Paneth/patología , Células Madre/patologíaRESUMEN
It is well established that homeostasis of the intestinal epithelium becomes dysregulated during gastrointestinal helminth infection and is under immune control. An increase in both enterocyte proliferation and the subsequent generation of crypt hyperplasia are hallmarks of chronic infection with Trichuris muris, a large intestinal dwelling nematode. The effect of this parasitic infection on apoptosis induction in the large intestine and its regulation has been neglected. To address this, mice of resistant and susceptible phenotypes were infected with different doses of T. muris, and the levels of epithelial cell apoptosis were determined. It is clear that apoptosis is induced during chronic T. muris infection. This occurs mainly at the base of the cecal crypt, within the stem cell region. The level of apoptosis induced is independent of worm number, suggesting that it is not a consequence of worm-induced damage but rather a mechanism for controlling cell number within the crypt. Neutralization of both gamma interferon and tumor necrosis factor alpha caused a significant reduction in the levels of apoptosis, showing that proinflammatory cytokines generated in response to chronic infection play an important role in apoptosis induction in this system. It is proposed that the generation of proinflammatory cytokines during chronic T. muris infection may play a positive role, by promoting intestinal epithelial cell apoptosis, to counter infection-induced epithelial hyperplasia.
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Apoptosis , Células Epiteliales/patología , Mucosa Intestinal/patología , Intestino Grueso/patología , Tricuriasis/inmunología , Tricuriasis/patología , Animales , Proliferación Celular , Modelos Animales de Enfermedad , Susceptibilidad a Enfermedades , Inmunidad Innata , Inmunohistoquímica , Interferón gamma/antagonistas & inhibidores , Interferón gamma/metabolismo , Ratones , Ratones Endogámicos AKR , Ratones Endogámicos BALB C , Ratones Endogámicos C57BL , Ratones SCID , Receptores Tipo I de Factores de Necrosis Tumoral/deficiencia , Receptores Tipo I de Factores de Necrosis Tumoral/metabolismo , Receptores Tipo II del Factor de Necrosis Tumoral/deficiencia , Receptores Tipo II del Factor de Necrosis Tumoral/metabolismo , Trichuris/inmunología , Factor de Necrosis Tumoral alfa/metabolismoRESUMEN
Id transcription factors control proliferation, differentiation and apoptosis by inhibiting the DNA binding of basic helix-loop-helix transcription factors. Increased expression of Id proteins promotes proliferation, inhibits differentiation, and is associated with intestinal tumorigenesis. We aimed to determine how Helicobacter pylori may alter the expression of Id proteins by gastric epithelial cells: it was hypothesised that H. pylori, a known carcinogen, would result in increased expression of one or more Id family members. In vitro and in vivo models of infection were employed, including treatment of AGS gastric epithelial cells with wild-type H. pylori strains, 60190 and SS1, and Mongolian gerbils infected with H. pylori SS1. A small cohort of human gastric mucosal biopsies was also examined. Treatment of AGS cells with H. pylori resulted in down-regulation of Id1 and Id3. Unexpectedly, expression of the main target of Id proteins, the basic helix-loop-helix transcription factor E2A, was also suppressed, with an associated decrease in E-box binding activity. In contrast, H. pylori induced the expression of the CDK inhibitor p21(WAF-1/cip1), and the homeobox transcription factor, Cdx2, an early marker of intestinal metaplasia of the stomach epithelium. Gastric epithelium from H. pylori-infected gerbils demonstrated similar changes, with decreased Id2, Id3 and E2A, and elevated p21(WAF-1/cip1) expression. In human gastric epithelium also, H. pylori infection was associated with reduced Id and E2A expression. In conclusion, H. pylori alters the expression of Id proteins, in vitro and in vivo; it is hypothesised that these changes contribute to H. pylori-associated pathologies.
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Infecciones por Helicobacter/metabolismo , Helicobacter pylori/fisiología , Proteínas Inhibidoras de la Diferenciación/metabolismo , Adolescente , Adulto , Anciano , Animales , Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico/metabolismo , Biopsia , Western Blotting , Línea Celular Tumoral , Inhibidor p21 de las Quinasas Dependientes de la Ciclina/metabolismo , Proteínas de Unión al ADN/metabolismo , Regulación hacia Abajo , Dispepsia/microbiología , Dispepsia/patología , Células Epiteliales/microbiología , Células Epiteliales/patología , Femenino , Gerbillinae , Infecciones por Helicobacter/microbiología , Infecciones por Helicobacter/patología , Proteínas de Homeodominio/metabolismo , Humanos , Inmunohistoquímica , Proteínas Inhibidoras de la Diferenciación/genética , Persona de Mediana Edad , ARN/genética , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Estómago/patologíaRESUMEN
Breast epithelial stem cells are thought to be the primary targets in the etiology of breast cancer. Since breast cancers mostly express estrogen and progesterone receptor (ERalpha and PR), we examined the biology of these ERalpha/PR-positive cells and their relationship to stem cells in normal human breast epithelium. We employed several complementary approaches to identify putative stem cell markers, to characterise an isolated stem cell population and to relate these to cells expressing the steroid receptors ERalpha and PR. Using DNA radiolabelling in human tissue implanted into athymic nude mice, a population of label-retaining cells were shown to be enriched for the putative stem cell markers p21(CIP1) and Msi-1, the human homolog of Drosophila Musashi. Steroid receptor-positive cells were found to co-express these stem cell markers together with cytokeratin 19, another putative stem cell marker in the breast. Human breast epithelial cells with Hoechst dye-effluxing "side population" (SP) properties characteristic of mammary stem cells in mice were demonstrated to be undifferentiated "intermediate" cells by lack of expression of myoepithelial and luminal apical membrane markers. These SP cells were 6-fold enriched for ERalpha-positive cells and expressed several fold higher levels of the ERalpha, p21(CIP1) and Msi1 genes than non-SP cells. In contrast to non-SP cells, SP cells formed branching structures in matrigel which included cells of both luminal and myoepithelial lineages. The data suggest a model where scattered steroid receptor-positive cells are stem cells that self-renew through asymmetric cell division and generate patches of transit amplifying and differentiated cells.
Asunto(s)
Mama/citología , Células Epiteliales/metabolismo , Receptor alfa de Estrógeno/metabolismo , Receptores de Progesterona/metabolismo , Células Madre/metabolismo , Análisis de Varianza , Animales , Autorradiografía , Proteínas de Ciclo Celular/metabolismo , Diferenciación Celular/fisiología , Células Cultivadas , Inhibidor p21 de las Quinasas Dependientes de la Ciclina , Cartilla de ADN , Femenino , Técnica del Anticuerpo Fluorescente , Humanos , Inmunohistoquímica , Queratinas/metabolismo , Ratones , Ratones Desnudos , Proteínas del Tejido Nervioso/metabolismo , Proteínas de Unión al ARN/metabolismo , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Fase S/fisiología , Células Madre/citologíaRESUMEN
Stem cells are the crucial cells upon which the entire tissue is dependent. Here we define and discuss what is meant by and known about keratinocyte stem cells. One way in which these cells have been studied is by their ability to retain radioactivity labelled thymidine for long periods of time (label retaining cells, LRCs). The underlying mechanism has been assumed in the past to be slow cycling but a more likely explanation is the selective segregation of old and new DNA strands (Cairns's hypothesis). Experiments in the small intestine indicate that the stem cells here are selectively sorting their DNA and becoming LRCs. A possible role for p53 in stem cell biology is presented.
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Genoma , Queratinocitos/fisiología , Fenómenos Fisiológicos de la Piel , Células Madre/fisiología , Animales , División Celular/genética , Humanos , Queratinocitos/citología , Células Madre/citologíaRESUMEN
Epithelial tissues are highly polarized, with the proliferative compartment subdivided into units of proliferation in many instances. My interests have been in trying to understand how many cellular constituents exist, what their function is, and what the intercommunicants are that ensure appropriate steady-state cell replacement rates. Radiation has proven to be a valuable tool to induce cell death, reproductive sterilization, and regenerative proliferation in these systems, the responses to which can provide information on the number of regenerative cells (a function associated with stem cells). Such studies have helped define the epidermal proliferative units and the structurally similar units on the dorsal surface of the tongue. The radiation responses considered in conjunction with a wide range of cell kinetic, lineage tracking and somatic mutation studies together with complex mathematical modeling provide insights into the functioning of the proliferative units (crypts) of the small intestine. Comparative studies have then been undertaken with the crypts in the large bowel. In the small intestine, in which cancer rarely develops, various protective mechanisms have evolved to ensure the genetic integrity of the stem cell compartment. Stem cells in the small intestinal crypts are intolerant of genotoxic damage (including that induced by very low doses of radiation); they do not undergo cell cycle arrest and repair but commit an altruistic TP53-dependent cell suicide (apoptosis). This process is compromised in the large bowel by BCL2 expression. Recent studies have suggested a second genome protection mechanism operating in the stem cells of the small intestinal crypts that may also have a TP53 dependence. Such studies have allowed the cell lineages and genome protection mechanisms operating the small intestinal crypts to be defined.
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Fenómenos Fisiológicos Celulares/efectos de la radiación , Mucosa Intestinal/fisiología , Mucosa Intestinal/efectos de la radiación , Intestino Delgado/fisiología , Intestino Delgado/efectos de la radiación , Radiación Ionizante , Células Madre/fisiología , Células Madre/efectos de la radiación , Animales , Apoptosis/efectos de la radiación , HumanosRESUMEN
Pathbase is a database that stores images of the abnormal histology associated with spontaneous and induced mutations of both embryonic and adult mice including those produced by transgenesis, targeted mutagenesis and chemical mutagenesis. Images of normal mouse histology and strain-dependent background lesions are also available. The database and the images are publicly accessible (http://www.pathbase.net) and linked by anatomical site, gene and other identifiers to relevant databases; there are also facilities for public comment and record annotation. The database is structured around a novel ontology of mouse disorders (MPATH) and provides high-resolution downloadable images of normal and diseased tissues that are searchable through orthogonal ontologies for pathology, developmental stage, anatomy and gene attributes (GO terms), together with controlled vocabularies for type of genetic manipulation or mutation, genotype and free text annotation for mouse strain and additional attributes. The database is actively curated and data records assessed by pathologists in the Pathbase Consortium before publication. The database interface is designed to have optimal browser and platform compatibility and to interact directly with other web-based mouse genetic resources.
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Bases de Datos Factuales , Enfermedad , Ratones , Mutación , Patología , Animales , Biología Computacional , Genotipo , Almacenamiento y Recuperación de la Información , Internet , Fenotipo , Vocabulario ControladoRESUMEN
Poly(ADP-ribose) polymerase-1 (PARP-1) is a key enzyme mediating the cellular response to DNA strand breaks. It plays a critical role in genomic stability and survival of proliferating cells in culture undergoing DNA damage. Intestinal epithelium is the most proliferative tissue in the mammalian body and its stem cells show extreme sensitivity to low-level genotoxic stress. We investigated the role of PARP-1 in the in vivo damage response of intestinal stem cells in crypts of PARP-1-/- and control mice following whole-body gamma-irradiation (1 Gy). In the PARP-1-/- mice there was a significant delay during the first 6 h in the transient p53 accumulation in stem cells whereas an increased number of cells were positive for p21(CIP1/WAF1). Either no or only marginal differences were noted in MDM2 expression, apoptosis, induction of or recovery from mitotic blockage, or inhibition of DNA synthesis. We further observed a dose-dependent reduction in crypt survival measured at 4 days post-irradiation in control mice, and this crypt-killing effect was significantly potentiated in PARP-1-/- mice. Our results thus establish that PARP-1 acts as a survival factor for intestinal stem cells in vivo and suggest a functional link with early p53 and p21(CIP1/WAF1) responses.
Asunto(s)
Células Epiteliales/efectos de la radiación , Intestinos/efectos de la radiación , Proteínas Nucleares , Poli(ADP-Ribosa) Polimerasas/metabolismo , Células Madre/efectos de la radiación , Animales , Apoptosis/efectos de la radiación , Supervivencia Celular/efectos de la radiación , Inhibidor p21 de las Quinasas Dependientes de la Ciclina , Ciclinas/metabolismo , Replicación del ADN/efectos de la radiación , Células Epiteliales/citología , Células Epiteliales/enzimología , Células Epiteliales/metabolismo , Rayos gamma , Eliminación de Gen , Mucosa Intestinal/metabolismo , Intestinos/citología , Intestinos/enzimología , Ratones , Ratones Noqueados , Mitosis/efectos de la radiación , Poli(ADP-Ribosa) Polimerasas/genética , Proteínas Proto-Oncogénicas/metabolismo , Proteínas Proto-Oncogénicas c-mdm2 , Células Madre/citología , Células Madre/enzimología , Células Madre/metabolismo , Factores de Tiempo , Proteína p53 Supresora de Tumor/metabolismoRESUMEN
Breast epithelial stem cells are thought to be the primary targets in the aetiology of breast cancer. As breast cancers are predominantly oestrogen and progesterone receptor-positive (ERalpha/PR+), we investigated the biology of ERalpha/PR+ cells and their relationship to stem cells in normal human breast epithelium. Several complementary approaches were used to characterize the stem-cell population and relate it to ERalpha/PR+ cells, including dual label colocalization on tissue sections, isolation of a Hoechst dye-effluxing 'side population' using flow cytometry, and examination of DNA label retention. The intermediate or suprabasal population suggested by others to be breast stem cells comprises ERalpha/PR+ cells that coexpress the putative stem-cell markers including cytokeratin 19. Human breast epithelial cells with Hoechst dye-effluxing 'side population' properties characteristic of mammary stem cells in mice were demonstrated by lack of expression of myoepithelial and luminal cell-specific antigens such as CALLA and MUC1 to be undifferentiated cells. Using DNA radiolabelling of human tissue implanted into athymic nude mice, a population of label-retaining putative stem cells (LRC) were shown to be enriched for cells expressing the putative stem-cell markers p21CIP1/WAF1 and Musashi-1, which, interestingly, were expressed in separate subpopulations of ERalpha/PR+ cells. Finally, expression patterns of Musashi-1 and Notch-1 in relation to ERalpha/PR+ and adjacent proliferating cells suggest that the evolutionarily conserved Delta/Notch signalling pathway regulates asymmetric division of the putative stem-cell population. The data suggest a model in which ERalpha/PR+ cells scattered through the epithelium are stem cells that self-renew through asymmetric cell division and generate patches of transit amplifying and differentiated cells. ERalpha/PR+ breast cancers exhibit loss of the two key regulators of asymmetric cell division, Musashi-1 and Notch-1 and thus may arise from symmetric division of the ERalpha/PR+ stem cell.
Asunto(s)
Mama/citología , Células Epiteliales/citología , Células Epiteliales/fisiología , Células Madre/citología , Células Madre/fisiología , HumanosRESUMEN
Adult tissue stem cells are defined and some current controversies are discussed. These crucial cells are responsible for all cell production in renewing tissues, and play a vital role in tissue regeneration. Although reliable stem cell markers are generally unavailable for adult epithelial tissues, the small intestinal crypts are an excellent in vivo model system to study stem cells. Within this tissue, the stem cells have a very well-defined cell position, allowing accurate definition of stem cell specific events. Clonal regeneration assays for the small intestine allow stem cell survival and functional competence to be studied. The ultimate lineage ancestor stem cells are extremely efficiently protected from genetic damage, which accounts for the low cancer incidence in this tissue. Some of the regulatory networks governing stem and transit cell behaviour are beginning to be understood and it is postulated that p53 plays a crucial role in these processes.
Asunto(s)
Intestino Delgado/citología , Células Madre/citología , Células Madre/efectos de los fármacos , Adulto , Animales , Diferenciación Celular , División Celular , Linaje de la Célula , Epitelio/efectos de los fármacos , Epitelio/fisiología , Humanos , Intestino Delgado/fisiología , Modelos Biológicos , Células Madre/fisiologíaRESUMEN
There are few reliable markers for adult stem cells and none for those of the intestinal epithelium. Previously, indirect experimental approaches have predicted stem cell position and numbers. The Musashi-1 (Msi-1) gene encodes an RNA binding protein associated with asymmetric divisions in neural progenitor cells. Two-day-old, adult, and 4.5 h, 1-, 2-, 4- and 12-day post-irradiation samples of BDF1 mouse small intestine, together with some samples of mouse colon were stained with a rat monoclonal antibody to Musashi-1 (14 H-1). Min ( + / - ) mice with small intestinal adenomas of varying sizes were also analysed. Samples of human small and large bowel were also studied but the antibody staining was weak. Musashi-1 expression was observed using immunohistochemistry in neonatal, adult, and regenerating crypts with a staining pattern consistent with the predicted number and distribution of early lineage cells including the functional stem cells in these situations. Early dysplastic crypts and adenomas were also strongly Musashi-1 positive. In situ hybridization studies showed similar expression patterns for the Musashi mRNA and real-time quantitative RT-PCR showed dramatically more Msi-1 mRNA expression in Min tumours compared with adjacent normal tissue. These observations suggest that Musashi-1 is a marker of stem and early lineage progenitor cells in murine intestinal tissue.
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Biomarcadores , Mucosa Intestinal/citología , Proteínas del Tejido Nervioso/metabolismo , Proteínas de Unión al ARN/metabolismo , Células Madre/metabolismo , Adulto , Anciano , Animales , Linaje de la Célula , Niño , Rayos gamma , Humanos , Mucosa Intestinal/metabolismo , Mucosa Intestinal/efectos de la radiación , Neoplasias Intestinales/metabolismo , Neoplasias Intestinales/patología , Masculino , Ratones , Proteínas del Tejido Nervioso/genética , Proteínas de Unión al ARN/genética , Células Madre/citologíaAsunto(s)
Neoplasias Colorrectales/etiología , Proteínas del Citoesqueleto/fisiología , Mucosa Intestinal/citología , Transactivadores/fisiología , Factores de Transcripción/fisiología , Diferenciación Celular , Neoplasias Colorrectales/terapia , Humanos , Receptor EphB2/análisis , Receptor EphB3/análisis , Factores de Transcripción TCF , Proteína 2 Similar al Factor de Transcripción 7 , beta CateninaRESUMEN
For many years it has been widely accepted that stem cells play a crucial role in adult tissue maintenance. The concept that the renewing tissues of the body contain a small subcompartment of self-maintaining stem cells, upon which the entire tissue is dependent, is also now accepted as applicable to all renewing tissues. Gene therapy and tissue engineering are driving considerable interest in the clinical application of such hierarchically organized cellular compartments. Recent initial observations have provided a tantalizing insight into the large pluripotency of these cells. Indeed, scientists are now beginning to talk about the possible totipotency of some adult tissue stem cells. Such work is currently phenomenologic, but analysis of data derived from genomics and proteomics, identifying the crucial control signals involved, will soon provide a further impetus to stem cell biology with far reaching applications. The epidermis with its relatively simple structure, ease of accessibility, and the ability to grow its cells in vitro is one obvious target tissue for testing stem cell manipulation theories. It is crucial, however, that the normal keratinocyte stem cell is thoroughly characterized prior to attempting to manipulate its pluripotency. This commentary assesses the data generated to date and critically discusses the conclusions that have been drawn. Our current level of understanding, or lack of understanding, of the keratinocyte stem cell is reviewed.
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Queratinocitos/fisiología , Células Madre/fisiología , Biomarcadores , Ciclo Celular , Linaje de la Célula , Movimiento Celular , ADN/metabolismo , Folículo Piloso/citología , Humanos , Piel/citologíaRESUMEN
The stem cells in the crypts of the small intestinal mucosa divide about a thousand times during the lifespan of a laboratory mouse, and yet they show little evidence of any decline in proliferative potential and rarely develop carcinogenic mutations, suggesting that their genome is extremely well protected. Protection against DNA-replication-induced errors can be achieved by the selective sorting of old (template) and new DNA strands with all template strands retained in the stem cell line. The template strands in the stem cells can be labelled during development or during tissue regeneration using tritiated thymidine ((3)HTdR). Labelling newly synthesised strands with a different marker (bromodeoxyuridine, BrdUrd) allows segregation of the two markers to be studied. Template strand label is retained ((3)HTdR), whereas label in the newly synthesised strands (BrdUrd) is lost following the second division of the stem cell. Random errors may occur in the template strands owing to environmental elements. These are protected against by the altruistic cell suicide (apoptosis) of the cells incurring such errors. A final level of protection for the tissue compensates for excessive deletion of stem cells via the apoptosis pathway. This is achieved by a hierarchical age structure in the stem cell compartment, with some cells being able to efficiently repair DNA damage and hence being more radioresistant. The presence of these protective mechanisms ensures that the small intestine rarely develops cancer and that stem cells can sustain the extensive cell proliferation needed during life.