RESUMEN
Hematopoietic stem cells (HSCs) exist in a dormant state and progressively lose regenerative potency as they undergo successive divisions. Why this functional decline occurs and how this information is encoded is unclear. To better understand how this information is stored, we performed RNA sequencing on HSC populations differing only in their divisional history. Comparative analysis revealed that genes upregulated with divisions are enriched for lineage genes and regulated by cell-cycle-associated transcription factors, suggesting that proliferation itself drives lineage priming. Downregulated genes are, however, associated with an HSC signature and targeted by the Polycomb Repressive Complex 2 (PRC2). The PRC2 catalytic subunits Ezh1 and Ezh2 promote and suppress the HSC state, respectively, and successive divisions cause a switch from Ezh1 to Ezh2 dominance. We propose that cell divisions drive lineage priming and Ezh2 accumulation, which represses HSC signature genes to consolidate information on divisional history into memory.
Asunto(s)
División Celular , Linaje de la Célula , Hematopoyesis , Células Madre Hematopoyéticas/citología , Animales , División Celular/genética , Linaje de la Célula/genética , Autorrenovación de las Células , Cromatina/metabolismo , Proteína Potenciadora del Homólogo Zeste 2/metabolismo , Femenino , Regulación de la Expresión Génica , Hematopoyesis/genética , Homeostasis , Masculino , Ratones Endogámicos C57BL , Modelos Biológicos , Complejo Represivo Polycomb 2/genética , Complejo Represivo Polycomb 2/metabolismoRESUMEN
The induction of hematopoiesis in various cell types via transcription factor (TF) reprogramming has been demonstrated by several strategies. The eventual goal of these approaches is to generate a product for unmet needs in hematopoietic cell transplantation therapies. The most successful strategies hew closely to clues provided from developmental hematopoiesis in terms of factor expression and environmental cues. In this review, we aim to summarize the TFs that play important roles in developmental hematopoiesis primarily and to also touch on adult hematopoiesis. Several aspects of cellular and molecular biology coalesce in this process, with TFs and surrounding cellular signals playing a major role in the overall development of the hematopoietic lineage. We attempt to put these elements into the context of reprogramming and highlight their roles.
Asunto(s)
Microambiente Celular/fisiología , Crecimiento y Desarrollo/fisiología , Hematopoyesis/fisiología , Células Madre Hematopoyéticas/fisiología , Factores de Transcripción/fisiología , Animales , Linaje de la Célula/genética , Regulación del Desarrollo de la Expresión Génica , Crecimiento y Desarrollo/genética , Hematopoyesis/genética , Células Madre Hematopoyéticas/citología , Humanos , Nicho de Células Madre/fisiologíaRESUMEN
The cellular and molecular mechanisms underlying specification of human hematopoietic stem cells (HSCs) remain elusive. Strategies to recapitulate human HSC emergence in vitro are required to overcome limitations in studying this complex developmental process. Here, we describe a protocol to generate hematopoietic stem and progenitor-like cells from human dermal fibroblasts employing a direct cell reprogramming approach. These cells transit through a hemogenic intermediate cell-type, resembling the endothelial-to-hematopoietic transition (EHT) characteristic of HSC specification. Fibroblasts were reprogrammed to hemogenic cells via transduction with GATA2, GFI1B and FOS transcription factors. This combination of three factors induced morphological changes, expression of hemogenic and hematopoietic markers and dynamic EHT transcriptional programs. Reprogrammed cells generate hematopoietic progeny and repopulate immunodeficient mice for three months. This protocol can be adapted towards the mechanistic dissection of the human EHT process as exemplified here by defining GATA2 targets during the early phases of reprogramming. Thus, human hemogenic reprogramming provides a simple and tractable approach to identify novel markers and regulators of human HSC emergence. In the future, faithful induction of hemogenic fate in fibroblasts may lead to the generation of patient-specific HSCs for transplantation.
Asunto(s)
Reprogramación Celular , Fibroblastos/fisiología , Células Madre Hematopoyéticas/metabolismo , Factores de Transcripción/metabolismo , Animales , Adhesión Celular , Diferenciación Celular , Humanos , Ratones , Factores de Transcripción/genéticaRESUMEN
Transcription factor (TF)-based reprogramming of somatic tissues holds great promise for regenerative medicine. Previously, we demonstrated that the TFs GATA2, GFI1B, and FOS convert mouse and human fibroblasts to hemogenic endothelial-like precursors that generate hematopoietic stem progenitor (HSPC)-like cells over time. This conversion is lacking in robustness both in yield and biological function. Herein, we show that inclusion of GFI1 to the reprogramming cocktail significantly expands the HSPC-like population. AFT024 coculture imparts functional potential to these cells and allows quantification of stem cell frequency. Altogether, we demonstrate an improved human hemogenic induction protocol that could provide a valuable human in vitro model of hematopoiesis for disease modeling and a platform for cell-based therapeutics. DATABASE: Gene expression data are available in the Gene Expression Omnibus (GEO) database under the accession number GSE130361.
Asunto(s)
Diferenciación Celular/genética , Reprogramación Celular/genética , Hemangioblastos/citología , Células Madre Hematopoyéticas/citología , Animales , Técnicas de Cocultivo/métodos , Fibroblastos/citología , Fibroblastos/metabolismo , Factor de Transcripción GATA2/genética , Regulación del Desarrollo de la Expresión Génica/genética , Hemangioblastos/metabolismo , Hematopoyesis/genética , Células Madre Hematopoyéticas/metabolismo , Humanos , Ratones , Proteínas Proto-Oncogénicas/genética , Proteínas Proto-Oncogénicas c-fos/genética , Proteínas Represoras/genética , Factores de Transcripción/genéticaRESUMEN
A multitude of signals are coordinated to maintain self-renewal in embryonic stem cells (ESCs). To unravel the essential internal and external signals required for sustaining the ESC state, we expand upon a set of ESC pluripotency-associated phosphoregulators (PRs) identified previously by short hairpin RNA (shRNA) screening. In addition to the previously described Aurka, we identify 4 additional PRs (Bub1b, Chek1, Ppm1g, and Ppp2r1b) whose depletion compromises self-renewal and leads to consequent differentiation. Global gene expression profiling and computational analyses reveal that knockdown of the 5 PRs leads to DNA damage/genome instability, activating p53 and culminating in ESC differentiation. Similarly, depletion of genome integrity-associated genes involved in DNA replication and checkpoint, mRNA processing, and Charcot-Marie-Tooth disease lead to compromise of ESC self-renewal via an increase in p53 activity. Our studies demonstrate an essential link between genomic integrity and developmental cell fate regulation in ESCs.
Asunto(s)
Diferenciación Celular/genética , Células Madre Embrionarias/fisiología , Inestabilidad Genómica , Animales , Proteínas de Ciclo Celular/genética , Proteínas de Ciclo Celular/fisiología , Línea Celular , Daño del ADN , Perfilación de la Expresión Génica , Prueba de Complementación Genética , Ratones , Fosfoproteínas/genética , Fosfoproteínas/fisiología , ARN Interferente Pequeño , Transducción de Señal , Proteína p53 Supresora de Tumor/fisiologíaRESUMEN
During development, hematopoietic stem and progenitor cells (HSPCs) arise from specialized endothelial cells by a process termed endothelial-to-hematopoietic transition (EHT). The genetic program driving human HSPC emergence remains largely unknown. We previously reported that the generation of hemogenic precursor cells from mouse fibroblasts recapitulates developmental hematopoiesis. Here, we demonstrate that human fibroblasts can be reprogrammed into hemogenic cells by the same transcription factors. Induced cells display dynamic EHT transcriptional programs, generate hematopoietic progeny, possess HSPC cell surface phenotype, and repopulate immunodeficient mice for 3 months. Mechanistically, GATA2 and GFI1B interact and co-occupy a cohort of targets. This cooperative binding is reflected by engagement of open enhancers and promoters, initiating silencing of fibroblast genes and activating the hemogenic program. However, GATA2 displays dominant and independent targeting activity during the early phases of reprogramming. These findings shed light on the processes controlling human HSC specification and support generation of reprogrammed HSCs for clinical applications.
Asunto(s)
Reprogramación Celular , Hemangioblastos/citología , Hemangioblastos/metabolismo , Factores de Transcripción/metabolismo , Adulto , Secuencia de Bases , Elementos de Facilitación Genéticos/genética , Fibroblastos/metabolismo , Factor de Transcripción GATA2/metabolismo , Regulación de la Expresión Génica , Células HEK293 , Trasplante de Células Madre Hematopoyéticas , Células Madre Hematopoyéticas/metabolismo , Humanos , Recién Nacido , Fenotipo , Regiones Promotoras Genéticas/genética , Unión ProteicaRESUMEN
Osteosarcoma (OS), the most common primary bone tumor, is highly metastatic with high chemotherapeutic resistance and poor survival rates. Using induced pluripotent stem cells (iPSCs) generated from Li-Fraumeni syndrome (LFS) patients, we investigate an oncogenic role of secreted frizzled-related protein 2 (SFRP2) in p53 mutation-associated OS development. Interestingly, we find that high SFRP2 expression in OS patient samples correlates with poor survival. Systems-level analyses identified that expression of SFRP2 increases during LFS OS development and can induce angiogenesis. Ectopic SFRP2 overexpression in normal osteoblast precursors is sufficient to suppress normal osteoblast differentiation and to promote OS phenotypes through induction of oncogenic molecules such as FOXM1 and CYR61 in a ß-catenin-independent manner. Conversely, inhibition of SFRP2, FOXM1, or CYR61 represses the tumorigenic potential. In summary, these findings demonstrate the oncogenic role of SFRP2 in the development of p53 mutation-associated OS and that inhibition of SFRP2 is a potential therapeutic strategy.
Asunto(s)
Neoplasias Óseas/genética , Carcinogénesis/genética , Síndrome de Li-Fraumeni/patología , Proteínas de la Membrana/genética , Osteosarcoma/genética , Proteína p53 Supresora de Tumor/genética , Animales , Neoplasias Óseas/patología , Línea Celular Tumoral , Proteína 61 Rica en Cisteína/antagonistas & inhibidores , Proteína 61 Rica en Cisteína/genética , Proteína Forkhead Box M1/antagonistas & inhibidores , Proteína Forkhead Box M1/genética , Humanos , Células Madre Pluripotentes Inducidas/metabolismo , Síndrome de Li-Fraumeni/genética , Masculino , Proteínas de la Membrana/antagonistas & inhibidores , Ratones , Ratones Desnudos , Neovascularización Patológica/genética , Osteoblastos/citología , Osteosarcoma/patologíaRESUMEN
Definitive hematopoiesis emerges via an endothelial-to-hematopoietic transition in the embryo and placenta; however, the precursor cells to hemogenic endothelium are not defined phenotypically. We previously demonstrated that the induction of hematopoietic progenitors from fibroblasts progresses through hemogenic precursors that are Prom1(+)Sca1(+)CD34(+)CD45(-) (PS34CD45(-)). Guided by these studies, we analyzed mouse placentas and identified a population with this phenotype. These cells express endothelial markers, are heterogeneous for early hematopoietic markers, and localize to the vascular labyrinth. Remarkably, global gene expression profiles of PS34CD45(-) cells correlate with reprogrammed precursors and establish a hemogenic precursor cell molecular signature. PS34CD45(-) cells are also present in intra-embryonic hemogenic sites. After stromal co-culture, PS34CD45(-) cells give rise to all blood lineages and engraft primary and secondary immunodeficient mice. In summary, we show that reprogramming reveals a phenotype for in vivo precursors to hemogenic endothelium, establishing that direct in vitro conversion informs developmental processes in vivo.
Asunto(s)
Diferenciación Celular/fisiología , Linaje de la Célula/fisiología , Reprogramación Celular , Hematopoyesis/genética , Células Madre Hematopoyéticas/citología , Células Madre Embrionarias de Ratones/citología , Animales , Células Cultivadas , Endotelio/metabolismo , Femenino , Fibroblastos/citología , Ratones , Ratones Endogámicos C57BL , EmbarazoRESUMEN
Previous attempts to either generate or expand hematopoietic stem cells (HSCs) in vitro have involved either ex vivo expansion of pre-existing patient or donor HSCs or de novo generation from pluripotent stem cells (PSCs), comprising both embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs). iPSCs alleviated ESC ethical issues but attempts to generate functional mature hematopoietic stem and progenitor cells (HSPCs) have been largely unsuccessful. New efforts focus on directly reprogramming somatic cells into definitive HSCs and HSPCs. To meet clinical needs and to advance drug discovery and stem cell therapy, alternative approaches are necessary. In this review, we synthesize the strategies used and the key findings made in recent years by those trying to make an HSC.
Asunto(s)
Células Madre Hematopoyéticas/fisiología , Animales , Técnicas de Cultivo de Célula , Células Cultivadas , Reprogramación Celular , Células Madre Embrionarias/fisiología , Humanos , Células Madre Pluripotentes Inducidas/fisiologíaRESUMEN
Somatic PTPN11 mutations cause juvenile myelomonocytic leukemia (JMML). Germline PTPN11 defects cause Noonan syndrome (NS), and specific inherited mutations cause NS/JMML. Here, we report that hematopoietic cells differentiated from human induced pluripotent stem cells (hiPSCs) harboring NS/JMML-causing PTPN11 mutations recapitulated JMML features. hiPSC-derived NS/JMML myeloid cells exhibited increased signaling through STAT5 and upregulation of miR-223 and miR-15a. Similarly, miR-223 and miR-15a were upregulated in 11/19 JMML bone marrow mononuclear cells harboring PTPN11 mutations, but not those without PTPN11 defects. Reducing miR-223's function in NS/JMML hiPSCs normalized myelogenesis. MicroRNA target gene expression levels were reduced in hiPSC-derived myeloid cells as well as in JMML cells with PTPN11 mutations. Thus, studying an inherited human cancer syndrome with hiPSCs illuminated early oncogenesis prior to the accumulation of secondary genomic alterations, enabling us to discover microRNA dysregulation, establishing a genotype-phenotype association for JMML and providing therapeutic targets.
Asunto(s)
Células Madre Pluripotentes Inducidas/citología , Leucemia Mielomonocítica Juvenil/metabolismo , Células Mieloides/citología , Proteína Tirosina Fosfatasa no Receptora Tipo 11/genética , Lectina 3 Similar a Ig de Unión al Ácido Siálico/metabolismo , Células Cultivadas , Células HEK293 , Humanos , Células Madre Pluripotentes Inducidas/metabolismo , Leucemia Mielomonocítica Juvenil/genética , Leucemia Mielomonocítica Juvenil/patología , MicroARNs/genética , Mutación , Células Mieloides/metabolismo , Lectina 3 Similar a Ig de Unión al Ácido Siálico/genética , Regulación hacia ArribaRESUMEN
Multiple cell types that share a common origin cooperate to form a supportive niche for stem cells that give rise to blood and to the cells of the immune system.
Asunto(s)
Nicho de Células Madre , Animales , Embrión de Mamíferos/citología , Desarrollo Embrionario , Humanos , Células Madre Mesenquimatosas/citología , Ratones , Modelos Biológicos , Nestina/metabolismoRESUMEN
Many signals must be integrated to maintain self-renewal and pluripotency in embryonic stem cells (ESCs) and to enable induced pluripotent stem cell (iPSC) reprogramming. However, the exact molecular regulatory mechanisms remain elusive. To unravel the essential internal and external signals required for sustaining the ESC state, we conducted a short hairpin (sh) RNA screen of 104 ESC-associated phosphoregulators. Depletion of one such molecule, aurora kinase A (Aurka), resulted in compromised self-renewal and consequent differentiation. By integrating global gene expression and computational analyses, we discovered that loss of Aurka leads to upregulated p53 activity that triggers ESC differentiation. Specifically, Aurka regulates pluripotency through phosphorylation-mediated inhibition of p53-directed ectodermal and mesodermal gene expression. Phosphorylation of p53 not only impairs p53-induced ESC differentiation but also p53-mediated suppression of iPSC reprogramming. Our studies demonstrate an essential role for Aurka-p53 signaling in the regulation of self-renewal, differentiation, and somatic cell reprogramming.
Asunto(s)
Células Madre Embrionarias/metabolismo , Células Madre Pluripotentes/metabolismo , Proteínas Serina-Treonina Quinasas/metabolismo , Transducción de Señal , Proteína p53 Supresora de Tumor/metabolismo , Animales , Aurora Quinasa A , Aurora Quinasas , Diferenciación Celular , Línea Celular , Proliferación Celular , Células Madre Embrionarias/citología , Células HEK293 , Humanos , Ratones , Ratones Noqueados , Fosforilación , Células Madre Pluripotentes/citología , Proteínas Serina-Treonina Quinasas/antagonistas & inhibidores , Proteína p53 Supresora de Tumor/deficiencia , Proteína p53 Supresora de Tumor/genética , XenopusRESUMEN
The role of Wnt signaling in hematopoietic stem cell fate decisions remains controversial. We elected to dysregulate Wnt signaling from the perspective of the stem cell niche by expressing the pan Wnt inhibitor, Wnt inhibitory factor 1 (Wif1), specifically in osteoblasts. Here we report that osteoblastic Wif1 overexpression disrupts stem cell quiescence, leading to a loss of self-renewal potential. Primitive stem and progenitor populations were more proliferative and elevated in bone marrow and spleen, manifesting an impaired ability to maintain a self-renewing stem cell pool. Exhaustion of the stem cell pool was apparent only in the context of systemic stress by chemotherapy or transplantation of wild-type stem cells into irradiated Wif1 hosts. Paradoxically this is mediated, at least in part, by an autocrine induction of canonical Wnt signaling in stem cells on sequestration of Wnts in the environment. Additional signaling pathways are dysregulated in this model, primarily activated Sonic Hedgehog signaling in stem cells as a result of Wif1-induced osteoblastic expression of Sonic Hedgehog. We find that dysregulation of the stem cell niche by overexpression of an individual component impacts other unanticipated regulatory pathways in a combinatorial manner, ultimately disrupting niche mediated stem cell fate decisions.
Asunto(s)
Proteínas de la Matriz Extracelular/fisiología , Hematopoyesis/fisiología , Células Madre Hematopoyéticas/patología , Péptidos y Proteínas de Señalización Intercelular/fisiología , Osteoblastos/metabolismo , Proteínas Wnt/fisiología , Proteínas Adaptadoras Transductoras de Señales , Animales , Trasplante de Médula Ósea , Ciclo Celular , División Celular , Células Cultivadas/metabolismo , Proteínas de la Matriz Extracelular/deficiencia , Fluorouracilo/farmacología , Regulación del Desarrollo de la Expresión Génica , Proteínas Hedgehog/fisiología , Hematopoyesis/genética , Péptidos y Proteínas de Señalización Intercelular/deficiencia , Ratones , Ratones Congénicos , Ratones Transgénicos , Proteínas Recombinantes de Fusión/fisiología , Transducción de Señal , Nicho de Células Madre , Células del Estroma/metabolismoRESUMEN
To clarify the molecular pathways governing hematopoietic stem cell (HSC) development, we screened a fetal liver (FL) HSC cDNA library and identified a unique gene, hematopoietic expressed mammalian polycomb (hemp), encoding a protein with a zinc-finger domain and four malignant brain tumor (mbt) repeats. To investigate its biological role, we generated mice lacking Hemp (hemp(-/-)). Hemp(-/-) mice exhibited a variety of skeletal malformations and died soon after birth. In the FL, hemp was preferentially expressed in the HSC and early progenitor cell fractions, and analyses of fetal hematopoiesis revealed that the number of FL mononuclear cells, including HSCs, was reduced markedly in hemp(-/-) embryos, especially during early development. In addition, colony-forming and competitive repopulation assays demonstrated that the proliferative and reconstitution abilities of hemp(-/-) FL HSCs were significantly impaired. Microarray analysis revealed alterations in the expression levels of several genes implicated in hematopoietic development and differentiation in hemp(-/-) FL HSCs. These results demonstrate that Hemp, an mbt-containing protein, plays essential roles in HSC function and skeletal formation. It is also hypothesized that Hemp might be involved in certain congenital diseases, such as Klippel-Feil anomaly.
Asunto(s)
Desarrollo Óseo/fisiología , Huesos/embriología , Proteínas Cromosómicas no Histona/metabolismo , Embrión de Mamíferos/metabolismo , Regulación del Desarrollo de la Expresión Génica/fisiología , Células Madre Hematopoyéticas/metabolismo , Proteínas Represoras/metabolismo , Animales , Diferenciación Celular/fisiología , Proteínas Cromosómicas no Histona/genética , Embrión de Mamíferos/citología , Perfilación de la Expresión Génica , Hematopoyesis/fisiología , Síndrome de Klippel-Feil/genética , Síndrome de Klippel-Feil/metabolismo , Ratones , Ratones Noqueados , Análisis de Secuencia por Matrices de Oligonucleótidos , Proteínas Represoras/genéticaRESUMEN
Hematopoietic stem cells (HSC) have been defined by their ability to establish long-term hematopoiesis in myelo-ablated hosts. Prospective isolation using combinations of cell-surface markers and/or dye exclusion can yield highly purified and nearly homogeneous phenotypically defined cells that repopulate irradiated hosts. Although highly informative, these types of analyses may not necessarily reflect ongoing homeostatic hematopoiesis. HSCs are also described as being quiescent. This has been demonstrated by cell cycle analysis of phenotypically defined HSCs. Some studies have challenged the existence of truly quiescent HSCs, suggesting that they continuously cycle, albeit with very slow kinetics. Here we present a pulse-chase system based on the controllable incorporation of H2B-GFP into nucleosomes, which allows the identification, purification, and functional analysis of viable label-retaining cells. Our data complement and extend recent studies using similar strategies. These, together with our present studies, find a rare, quiescent or dormant subset within the population of stringently defined HSC phenotypes. To date, three types of niches, endosteal, vascular, and reticular, have been described; herein we review the cellular and spatial nature of these microenvironments. We propose that HSC label-retention combined with genetically manipulated stem cell niches will allow us to determine their anatomical architecture, to address HSC cell fate proliferation kinetics, and to begin to dissect the molecular cross talk among stem cells and niche cells in vivo during both normal and perturbed homeostasis.
Asunto(s)
Diferenciación Celular/genética , Células Madre Hematopoyéticas/clasificación , Células Madre Hematopoyéticas/fisiología , Modelos Genéticos , Nicho de Células Madre/fisiología , Animales , Humanos , RatonesRESUMEN
Nitric oxide (NO) signaling is important for the regulation of hematopoiesis. However, the role of individual NO synthase (NOS) isoforms is unclear. Our results indicate that the neuronal NOS isoform (nNOS) regulates hematopoiesis in vitro and in vivo. nNOS is expressed in adult bone marrow and fetal liver and is enriched in stromal cells. There is a strong correlation between expression of nNOS in a panel of stromal cell lines established from bone marrow and fetal liver and the ability of these cell lines to support hematopoietic stem cells; furthermore, NO donor can further increase this ability. The number of colonies generated in vitro from the bone marrow and spleen of nNOS-null mutants is increased relative to wild-type or inducible- or endothelial NOS knockout mice. These results describe a new role for nNOS beyond its action in the brain and muscle and suggest a model where nNOS, expressed in stromal cells, produces NO which acts as a paracrine regulator of hematopoietic stem cells.
Asunto(s)
Hematopoyesis/fisiología , Isoenzimas/metabolismo , Óxido Nítrico Sintasa de Tipo I/metabolismo , Animales , Células de la Médula Ósea/citología , Células de la Médula Ósea/enzimología , Células Cultivadas , Femenino , Hepatocitos/citología , Hepatocitos/enzimología , Isoenzimas/genética , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Óxido Nítrico Sintasa de Tipo I/genética , Comunicación Paracrina , Bazo/citología , Bazo/enzimología , Células Madre/citología , Células Madre/enzimología , Células del Estroma/citología , Células del Estroma/enzimologíaRESUMEN
We determined a transcriptional profile specific for clonal stromal mesenchymal stem cells from adult and fetal hematopoietic sites. To identify mesenchymal stem cell-like stromal cell lines, we evaluated the adipocytic, osteoblastic, chondrocytic, and vascular smooth muscle differentiation potential and also the hematopoietic supportive (stromal) capacity of six mouse stromal cell lines from adult bone marrow and day 14.5 fetal liver. We found that two lines were quadripotent and also supported hematopoiesis, BMC9 from bone marrow and AFT024 from fetal liver. We then ascertained the set of genes differentially expressed in the intersection set of AFT024 and BMC9 compared with those expressed in the union set of two negative control lines, 2018 and BFC012 (both from fetal liver); 346 genes were upregulated and 299 downregulated. Using Ingenuity software, we found two major gene networks with highly significant scores. One network contained downregulated genes that are known to be implicated in osteoblastic differentiation, proliferation, or transformation. The other network contained upregulated genes that belonged to two categories, cytoskeletal genes and genes implicated in the transcriptional machinery. The data extend the concept of stromal mesenchymal stem cells to clonal cell populations derived not only from bone marrow but also from fetal liver. The gene networks described should discriminate this cell type from other types of stem cells and help define the stem cell state.
Asunto(s)
Células de la Médula Ósea/metabolismo , Diferenciación Celular , Perfilación de la Expresión Génica , Redes Reguladoras de Genes/genética , Células Madre Mesenquimatosas/metabolismo , Células del Estroma/metabolismo , Animales , Western Blotting , Células de la Médula Ósea/fisiología , Línea Celular , Cartilla de ADN , Técnica del Anticuerpo Fluorescente , Hígado/citología , Células Madre Mesenquimatosas/fisiología , Ratones , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Células del Estroma/fisiologíaRESUMEN
A constellation of intrinsic and extrinsic cellular mechanisms regulates the balance of self-renewal and differentiation in all stem cells. Stem cells, their progeny, and elements of their microenvironment make up an anatomical structure that coordinates normal homeostatic production of functional mature cells. Here we discuss the stem cell niche concept, highlight recent progress, and identify important unanswered questions. We focus on three mammalian stem cell systems where large numbers of mature cells must be continuously produced throughout adult life: intestinal epithelium, epidermal structures, and bone marrow.
Asunto(s)
Folículo Piloso/citología , Células Madre Hematopoyéticas/citología , Células Madre Hematopoyéticas/fisiología , Mucosa Intestinal/citología , Células Madre/citología , Células Madre/fisiología , Animales , Células de la Médula Ósea/citología , Células de la Médula Ósea/fisiología , Diferenciación Celular , División Celular , Linaje de la Célula , Dermis/citología , Dermis/fisiología , Células Epidérmicas , Epidermis/fisiología , Homeostasis , Mesodermo/citología , Mesodermo/fisiología , Células Madre Multipotentes/citología , Células Madre Multipotentes/fisiología , Osteoblastos/fisiología , Transducción de Señal , Trasplante de Células MadreRESUMEN
Elucidation of the molecular mechanisms that are responsible for regulating the most basic properties of stem cells, self-renewal, and differentiation remains a major challenge in hematopoietic stem cell biology. We have taken a functional genomics approach towards revealing these mechanisms. Previous studies of the fetal liver genetic program led to the development of Stem Cell Database (SCDb, http://stemcell.princeton.edu), a resource for the stem cell community. These studies have been expanded to include the microenvironmental component of hematopoiesis and are the focus herein. In our efforts to study the microenvironmental component we have identified a stromal cell line, AFT024, which serves as a surrogate stem cell niche. The line provides a milieu that facilitates the maintenance of transplantable mouse and human stem cells as well as the generation of large populations of committed progenitors. In a manner mirroring the work done with the SCDb, we provide an online resource, Stromal Cell Database, StroCDB (http://stromalcell.princeton.edu), that is a compendium of information and data derived from biological and molecular studies of this surrogate niche. These include bioinformatic analyses of over 6000 clones derived from a subtracted library enriched for messages expressed in AFT024 as well as data derived from custom expression arrays developed from this library. Herein we describe these efforts and provide a guide for navigating the database and mining the information contained within.
Asunto(s)
Diferenciación Celular , Bases de Datos Factuales , Genómica , Células Madre Hematopoyéticas , Internet , Animales , Humanos , Ratones , Células del EstromaRESUMEN
PURPOSE OF REVIEW: Hematopoietic stem cells are thought to reside in discrete cellular spaces termed "niches." The cellular elements and matrix surrounding the stem cell within the niche constitute the microenvironment. The purpose of this review is to discuss recent reports that have begun to elucidate the geographic location, key cellular type, and molecular mechanisms operating in stem cell niches. RECENT FINDINGS: Studies that have revealed the osteoblast as the key in vivo cellular element of the adult stem cell niche are the most significant recent findings. Additional studies have highlighted the importance of the Notch and Wingless (Wnt) signaling pathways in the hematopoietic microenvironment. Genomewide expression screens have been used to perform molecular profiling of stromal cell lines that serve as surrogate stem cell niches. These profiles have revealed novel regulatory molecules and have reinforced the roles of classic developmental morphogens in the niche space. The transcriptional profiling from these screens suggests that it is highly unlikely that a single factor or signal transduction pathway will control stem cell properties. SUMMARY: This review highlights the recent advances made toward elucidating the cellular and molecular attributes of the hematopoietic stem cell niche. Complete knowledge of the cellular architecture and molecular mechanisms in stem cell niches is essential to understanding the basic stem cell behaviors of self-renewal and differentiation.