Asunto(s)
Sistema Hematopoyético/embriología , Animales , Médula Ósea/embriología , Linaje de la Célula , Embrión de Pollo , Sangre Fetal/citología , Factores de Crecimiento de Célula Hematopoyética/fisiología , Células Madre Hematopoyéticas/citología , Humanos , Hígado/embriología , Mesodermo/citología , Ratones , Membrana Vitelina/citología , Pez CebraRESUMEN
When proceeding normally, embryonic morphogenesis begins with germ layer formation through the process of gastrulation. Each primordial germ layer gives rise to a particular set of lineages. Until recently, it was considered that fate switches between germ layers were impossible. In the last two or three years however, a fair number of such switches have been described (Table I), the most spectacular of which entails the differentiation of neural stem cells into various derivatives. This unexpected plasticity opens important prospects for cell therapy. Stem cells, which are the cells that display this plasticity, are defined by the two properties of self renewal and pluripotency. They are set apart during ontogeny and are responsible for maintaining the homeostasis of a tissue. This notion, first established in the case of hematopoietic stem cells was later extended to other fast renewing cells, such as those in the intestinal epithelium or epidermis, and more recently to cells reputedly non-renewable, i.e. neurons. A new strategy has been described, which has the interesting feature that it can be applied to the isolation of stem cells from various lineages. It consists in sorting out cells on the basis of the efflux of Hoechst 33342 dye (Goodell et al., 1996). When a cell suspension stained with this dye is examined under two distinct wave lengths, a "side population" (SP), characterized by weak fluorescence, can be identified and sorted out. The dye efflux property of these cells is due to the activity of the mdr (multidrug resistance) gene, which encodes a protein responsible for the building of a canal which serves to extrude toxins from the cells. A means of distinguishing a truly multipotent stem cell from a progenitor committed to a specific lineage has been reported. This consists in the expression of the Pax7 gene. Pax7-/- mouse muscles have no satellite cells, i.e. they miss the cells normally responsible for the regeneration of muscle. In contrast they do have an SP population. These SP cells are incapable of differentiating into muscle, but give rise to 10 times more hematopoietic colonies, when cloned in vitro, than SP cells from wild type muscle do. Thus Pax7 appears to be a commitment gene, in the absence of which stem cells cannot become specified to the muscle lineage. As a conclusion, this review emphasizes various features of the recent findings: 1) the unexpected plasticity uncovered in recent years is restricted to the stem cells of each tissue; 2) the switch in phenotype has to be "forced" on these stem cells by drastic experimental conditions enforced in the host: often sublethal irradiation is superimposed on a genetic deficiency. Progress in this field, concerning both conceptual and applied aspects, will require the identification of the factors characterizing the niches which promote integration and fate switches of stem cells, probably a combination of growth factors and intercellular interactions. Finally a key issue, before any therapeutical applications can be considered, is how to control the proliferation of transplanted stem cells in their new environment.
Asunto(s)
Linaje de la Célula , Células Madre/citología , Miembro 1 de la Subfamilia B de Casetes de Unión a ATP/metabolismo , Adulto , Factores de Edad , Animales , Bencimidazoles/metabolismo , Transporte Biológico , Diferenciación Celular , Separación Celular , Embrión de Pollo , Células Clonales/citología , Técnicas de Cocultivo , Colorantes/metabolismo , Coturnix/embriología , Femenino , Citometría de Flujo , Estratos Germinativos/citología , Proteínas de Homeodominio/genética , Proteínas de Homeodominio/fisiología , Homeostasis , Humanos , Masculino , Ratones , Ratones Endogámicos mdx , Ratones Noqueados , Distrofia Muscular Animal/genética , Distrofia Muscular Animal/patología , Distrofia Muscular Animal/terapia , Sistema Nervioso/citología , Factor de Transcripción PAX7RESUMEN
We recently identified the allantois as a site producing hemopoietic and endothelial cells capable of colonizing the bone marrow of an engrafted host. Here, we report a detailed investigation of some early cytological and molecular processes occurring in the allantoic bud, which are probably involved in the production of angioblasts and hemopoietic cells. We show that the allantois undergoes a program characterized by the prominent expression of several "hemangioblastic" genes in the mesoderm accompanied by other gene patterns in the associated endoderm. VEGF-R2, at least from stage HH17 onward, is expressed and is shortly followed by transcription factors GATA-2, SCL/tal-1, and GATA-1. Blood island-like structures differentiate that contain both CD45(+) cells and cells accumulating hemoglobin; these structures look exactly like blood islands in the yolk sac. This hemopoietic process takes place before the establishment of a vascular network connecting the allantois to the embryo. As far as the endoderm is concerned, GATA-3 mRNA is found in the region where allantois will differentiate before the posterior instestinal portal becomes anatomically distinct. Shortly before the bud grows out, GATA-2 was expressed in the endoderm and, at the same time, the hemangioblastic program became initiated in the mesoderm. GATA-3 is detected at least until E8 and GATA-2 until E3 the latest stage examined for this factor. Using in vitro cultures, we show that allantoic buds, dissected out before the establishment of circulation between the bud and the rest of the embryo, produced erythrocytes of the definitive lineage. Moreover, using heterospecific grafts between chick and quail embryos, we demonstrate that the allantoic vascular network develops from intrinsic progenitors. Taken together, these results extend our earlier findings about the commitment of mesoderm to the endothelial and hemopoietic lineages in the allantois. The detection of a prominent GATA-3 expression restricted to the endoderm of the preallantoic region and allantoic bud, followed by that of GATA-2, is an interesting and novel information, in the context of organ formation and endoderm specification in the emergence of hemopoietic cells.
Asunto(s)
Alantoides/citología , Alantoides/embriología , Células Madre Hematopoyéticas/metabolismo , Mesodermo/citología , Proteínas Proto-Oncogénicas , Animales , Linaje de la Célula , Embrión de Pollo , Coturnix , Proteínas de Unión al ADN/metabolismo , Endodermo/metabolismo , Factores de Unión al ADN Específico de las Células Eritroides , Factor de Transcripción GATA2 , Factor de Transcripción GATA3 , Inmunohistoquímica , Hibridación in Situ , Antígenos Comunes de Leucocito/biosíntesis , Mesodermo/metabolismo , Modelos Biológicos , ARN Mensajero/metabolismo , Proteínas Tirosina Quinasas Receptoras/biosíntesis , Proteínas Tirosina Quinasas Receptoras/metabolismo , Receptores de Factores de Crecimiento/biosíntesis , Receptores de Factores de Crecimiento/metabolismo , Receptores de Factores de Crecimiento Endotelial Vascular , Factores de Tiempo , Transactivadores/metabolismo , Factores de Transcripción/metabolismoRESUMEN
A population of hematopoietic progenitors becomes committed within the embryo proper in the floor of the aorta (P-Sp/AGM in the mouse). In birds, this first aspect of intraembryonic hematopoiesis is prominent during embryonic day 3 (E3) as endothelium-associated "intra-aortic clusters." Between E6 and E8, diffuse hematopoiesis then occurs as "para-aortic foci" located in the dorsal mesentery ventral to the aorta. These foci are not associated with endothelium. Whether these two hematopoietic cell populations arise from distinct or common progenitors is not known. We could recently trace back the origin of intra-aortic clusters in the avian embryo by labeling aortic endothelial cells (EC) in vivo with acetylated low-density lipoproteins. This approach established the derivation of early intraembryonic hemopoietic cells from the endothelium, but did not indicate how long during ontogeny such a relationship may exist, since the progeny of EC labeled at E2 could be traced for 1-2 days at most. Here we report that, when E2 aortic ECs were infected prior to the formation of intra-aortic clusters with a nonreplicative LacZ-bearing retroviral vector, numerous cells were labeled in the para-aortic foci at E6. In contrast, when the retroviral vector was inoculated at E4 rather than E2, that is, after the disappearance of intra-aortic clusters, no cells in the para-aortic foci were labeled. Taken together, our results demonstrate that ECs from the aortic floor seed the two aspects of aorta-associated hemopoiesis and that these ECs with hemangioblastic potential are present only transiently in the aorta.
Asunto(s)
Aorta/embriología , Células Madre Hematopoyéticas/citología , Animales , Aorta/citología , Linaje de la Célula , Embrión de Pollo , Inmunohistoquímica , Ratones , RetroviridaeRESUMEN
The avian model provides an experimental approach for dissecting the origin, migrations and differentiation of cell lineages in early embryos. In this model, the endothelial network was shown to take place through two processes depending on the origin of endothelial precursors: vasculogenesis when angioblasts emerge in situ, angiogenesis when angioblasts are extrinsic. Two different mesodermal territories produce angioblasts, the somite which only gives rise to endothelial cells and the splanchnopleural mesoderm which also produces hemopoietic stem cells. Potentialities of the mesoderm are determined by a positive influence from the endoderm and a negative control from the ectoderm. The presence of circulating endothelial precursors in the embryonic blood stream is also detected.
Asunto(s)
Endotelio Vascular/fisiología , Modelos Biológicos , Neovascularización Fisiológica/fisiología , Animales , Embrión de Pollo , Estratos Germinativos , Hematopoyesis , Mesodermo , SomitosRESUMEN
The first hemopoietic cells were found in the yolk sac of mammalian embryos. Based on this observation it was postulated that hemopoietic stem cells are generated in this location. In the last few years, however, increasing evidence indicates that there is an independent site of hemopoietic cell generation, in the embryo proper, designated the paraaortic splanchnopleura/aorta, gonad, mesonephros region. Precursors of hemopoietic cells are found in this region before circulation is established between the yolk sac and the embryo proper. In contrast to the hemopoietic cells found in the yolk sac, the ones found in the embryo proper are multipotent lympho-myeloid precursors that rapidly acquire the capacity to reconstitute the hemopoietic system of adult irradiated recipients. We propose that these are the founder cells of adult definitive hematopoiesis.
Asunto(s)
Embrión de Mamíferos/citología , Hematopoyesis , Células Madre Hematopoyéticas/citología , Animales , Aorta/citología , Aorta/embriología , Femenino , Gónadas/citología , Gónadas/embriología , Mesonefro/citología , Mesonefro/embriología , Ratones , Pleura/citología , Pleura/embriología , EmbarazoRESUMEN
It is now widely accepted that hemopoietic cells born intraembryonically are the best candidates for the seeding of definitive hemopoietic organs. To further understand the mechanisms involved in the generation of definitive hemopoietic stem cells, we analysed the expression of the hemopoietic-related transcription factors Lmo2 and GATA-3 during the early steps of mouse development (7-12 dpc), with a particular emphasis on intraembryonic hemogenic sites. We show here that both Lmo2 and GATA-3 are present in the intraembryonic regions known to give rise to hemopoietic precursors in vitro and in vivo, suggesting that they act together at key points of hemopoietic development. (1) Lmo2 and GATA-3 are expressed in the caudal mesoderm during the phase of intraembryonic precursors determination. (2) A highly transient concomitant expression is observed in the caudal intraembryonic definitive endoderm, suggesting that these factors are involved in the specification of intraembryonic hemopoietic precursors. (3) Lmo2 and GATA-3 are expressed within the hemopoietic clusters located in the aortic floor during fetal liver colonisation. Furthermore, a strong GATA-3 signal allowed us to uncover previously unreported mesodermal aggregates beneath the aorta. A combined in situ and immunocytological analysis strongly suggests that ventral mesodermal GATA-3 patches are involved in the process of intraembryonic stem cell generation.
Asunto(s)
Proteínas de Unión al ADN/genética , Desarrollo Embrionario y Fetal , Regulación del Desarrollo de la Expresión Génica , Células Madre Hematopoyéticas/fisiología , Metaloproteínas/genética , Transactivadores/genética , Factores de Transcripción/genética , Proteínas Adaptadoras Transductoras de Señales , Alantoides/citología , Alantoides/fisiología , Animales , Aorta/embriología , Encéfalo/embriología , Factor de Transcripción GATA3 , Gástrula/citología , Gástrula/fisiología , Células Germinativas/fisiología , Células Madre Hematopoyéticas/citología , Proteínas con Dominio LIM , Mesodermo/fisiología , Ratones , Ratones Endogámicos BALB C , Transcripción GenéticaRESUMEN
We have investigated the developmental relationship of the hemopoietic and endothelial lineages in the floor of the chicken aorta, a site of hemopoietic progenitor emergence in the embryo proper. We show that, prior to the onset of hemopoiesis, the aortic endothelium uniformly expresses the endothelium-specific membrane receptor VEGF-R2. The onset of hemopoiesis can be precisely determined by detecting the common leukocyte antigen CD45. VEGF-R2 and CD45 are expressed in complementary fashion, namely the hemopoietic clusters in the floor of the aorta are CD45+/VEGF-R2-, while the rest of the aortic endothelium is CD45-/VEGF-R2+. To determine if the hemopoietic clusters are derived from EC, we tagged the E2 endothelial tree with a non-replicative retroviral vector and low density lipoproteins. Twenty four-48 hours later, labelled cells in the vascular tree were found to be either endothelial or hemopoietic but exceptionally both. Another 1-2 days later, groups of labelled cells appear in the dorsal mesentery within the hemopoietic "paraortic foci". Since no CD45+ cells were inserted among endothelial cells at the time of vascular labelling, hemopoietic clusters and foci must be concluded to derive from precursors with an endothelial phenotype.
Asunto(s)
Endotelio Vascular/fisiología , Hematopoyesis , Células Madre Hematopoyéticas/fisiología , Animales , Aorta/embriología , Diferenciación Celular , Embrión de Pollo , Endotelio Vascular/citología , Endotelio Vascular/embriología , Vectores Genéticos , Células Madre Hematopoyéticas/citología , Humanos , Antígenos Comunes de Leucocito/fisiología , Proteínas Tirosina Quinasas Receptoras/fisiología , Receptores de Factores de Crecimiento/fisiología , Receptores de Factores de Crecimiento Endotelial Vascular , RetroviridaeRESUMEN
The hypothesis that the endothelial and hemopoietic lineages have a common ontogenic origin is currently being revived. We have shown previously by means of quail/chick transplantations that two subsets of the mesoderm give rise to endothelial precursors: a dorsal one, the somite, produces pure angioblasts (angiopoietic potential), while a ventral one, the splanchnopleural mesoderm, gives rise to progenitors with a dual endothelial and hemopoietic potential (hemangiopoietic potential). To investigate the cellular and molecular controls of the angiopoietic/hemangiopoietic potential, we devised an in vivo assay based on the polarized homing of hemopoietic cell precursors to the floor of the aorta detectable in the quail/chick model. In the present work, quail mesoderm was grafted, after various pretreatments, onto the splanchnopleure of a chick host; the homing pattern and nature of graft-derived cells were analyzed thereafter using the QH1 monoclonal antibody which recognizes both quail endothelial and hemopoietic lineages. We report that transient contact with endoderm or ectoderm could change the behavior of cells derived from treated mesoderm, and that the effect of these germ layers could be mimicked by treatment with several growth factors VEGF, bFGF, TGF beta 1, EGF and TGF alpha, known to be involved in endothelial commitment and proliferation, and/or hemopoietic processes. The endoderm induced a hemangiopoietic potential in the associated mesoderm. Indeed, the association of paraxial or somatopleural mesoderm with endoderm promoted the "ventral homing" and the production of hemopoietic cells from mesoderm not normally endowed with this potential. The hemangiopoietic induction by endoderm could be mimicked by VEGF, bFGF and TGF beta 1. In contrast, a contact with ectoderm or EGF/TGF alpha treatments totally abrogated the hemangiopoietic capacity of the splanchnopleural mesoderm which produced pure angioblasts with no "ventral homing" behavior. We postulate that two gradients, one positive and one negative, modulate the angiopoietic/hemangiopoietic potential of the mesoderm.
Asunto(s)
Embrión no Mamífero/fisiología , Endotelio Vascular/embriología , Hematopoyesis , Células Madre Hematopoyéticas/fisiología , Mesodermo/fisiología , Neovascularización Fisiológica , Animales , Aorta/embriología , Embrión de Pollo , Coturnix , Ectodermo/citología , Ectodermo/fisiología , Endotelio Vascular/citología , Células Madre Hematopoyéticas/citología , Mesodermo/citología , Mesodermo/trasplante , Morfogénesis , Trasplante HeterólogoRESUMEN
In the mouse embryo, the generation of candidate progenitors for long-lasting hemopoiesis has been reported in the paraaortic splanchnopleura (P-Sp)/ aorta-gonad-mesonephros (AGM) region. Here, we address the following question: can the P-Sp/AGM environment support hemopoietic differentiation as well as generate stem cells, and, conversely, are other sites where hemopoietic differentiation occurs capable of generating stem cells? Although P-Sp/AGM generates de novo hemopoietic stem cells between 9.5 and 12.5 days post coitus (dpc), we show here that it does not support hemopoietic differentiation. Among mesoderm-derived sites, spleen and omentum were shown to be colonized by exogenous cells in the same fashion as the fetal liver. Cells colonizing the spleen were multipotent and pursued their evolution to committed progenitors in this organ. In contrast, the omentum, which was colonized by lymphoid-committed progenitors that did not expand, cannot be considered as a hemopoietic organ. From these data, stem cell generation appears incompatible with hemopoietic activity. At the peak of hemopoietic progenitor production in the P-Sp/AGM, between 10.5 and 11.5 dpc, multipotent cells were found at the exceptional frequency of 1 out of 12 total cells and 1 out of 4 AA4.1+ cells. Thus, progenitors within this region constitute a pool of undifferentiated hemopoietic cells readily accessible for characterization.
Asunto(s)
Aorta/embriología , Gónadas/embriología , Hematopoyesis/fisiología , Células Madre Hematopoyéticas/fisiología , Mesonefro/embriología , Animales , Aorta/citología , Diferenciación Celular , Células Cultivadas , Femenino , Citometría de Flujo , Gónadas/citología , Masculino , Mesonefro/citología , Ratones , Ratones Endogámicos BALB C , Ratones Endogámicos C57BL , Epiplón/embriología , Bazo/citología , Bazo/embriologíaRESUMEN
The avian model provides an experimental approach for dissecting the origin, migrations, and differentiation of cell lineages in early embryos. In this model, the endothelial network was shown to stem from both the somites and the splanchnopleural mesoderm. The somite line age produces only endothelial cells, whereas the splanchnopleural line age also produces hematopoietic stem cells. Potentialities of the mesoderm are determined by a positive influence from the endoderm and a negative influence from the ectoderm. A novel mode of blood-borne angiogenesis is also described.
Asunto(s)
Aves/embriología , Neovascularización Fisiológica , Animales , Diferenciación Celular , Embrión de Pollo/irrigación sanguínea , Endotelio Vascular/embriología , Mesodermo/fisiología , Codorniz/embriologíaRESUMEN
The hypothesis that the endothelial and hemopoietic lineages have a common ontogenic origin is currently being revived. We have shown previously by means of quail/chick transplantations that two subsets of the mesoderm give rise to endothelial precursors: a dorsal one, the somite, produces pure angioblasts (angiopoietic potential), while a ventral one, the splanchnopleural mesoderm, gives rise to progenitors with a dual endothelial and hemopoietic potential (hemangiopoietic potential). To investigate the cellular and molecular controls of the angiopoietic/hemangiopoietic potential, we devised an in vivo assay based on the polarized homing of hemopoietic cell precursors to the floor of the aorta detectable in the quail/chick model. In the present work, quail mesoderm was grafted, after various pretreatments, onto the splanchnopleure of a chick host; the homing pattern and nature of graft-derived QH1(+) cells were analyzed thereafter. We report that transient contact with endoderm or ectoderm could change the behavior of cells derived from treated mesoderm, and that the effect of these germ layers could be mimicked by treatment with several growth factors VEGF, bFGF, TGFbeta1, EGF and TGF(&agr;), known to be involved in endothelial commitment and proliferation, and/or hemopoietic processes. The endoderm induced a hemangiopoietic potential in the associated mesoderm. Indeed, the association of somatopleural mesoderm with endoderm promoted the 'ventral homing' and the production of hemopoietic cells from mesoderm not normally endowed with this potential. The hemangiopoietic induction by endoderm could be mimicked by VEGF, bFGF and TGFbeta1. In contrast, contact with ectoderm or EGF/TGF(&agr;) treatments totally abrogated the hemangiopoietic capacity of the splanchnopleural mesoderm, which produced pure angioblasts with no 'ventral homing' behaviour. We postulate that two gradients, one positive and one negative, modulate the angiopoietic/hemangiopoietic potential of the mesoderm.
Asunto(s)
Vasos Sanguíneos/embriología , Desarrollo Embrionario , Codorniz/embriología , Animales , Aorta/citología , Aorta/embriología , Vasos Sanguíneos/crecimiento & desarrollo , Embrión de Pollo , Ectodermo/metabolismo , Endodermo/metabolismo , Factor de Crecimiento Epidérmico/farmacología , Sustancias de Crecimiento/farmacología , Mesodermo/metabolismo , Técnicas de Cultivo de Órganos , Somitos/citología , Trasplante de Tejidos , Factor de Crecimiento Transformador alfa/farmacologíaRESUMEN
We have investigated the developmental relationship of the hemopoietic and endothelial lineages in the floor of the chicken aorta, a site of hemopoietic progenitor emergence in the embryo proper. We show that, prior to the onset of hemopoiesis, the aortic endothelium uniformly expresses the endothelium-specific membrane receptor VEGF-R2. The onset of hemopoiesis can be determined by detecting the common leukocyte antigen CD45. VEGF-R2 and CD45 are expressed in complementary fashion, namely the hemopoietic cluster-bearing floor of the aorta is CD45(+)/VEGF-R2(-), while the rest of the aortic endothelium is CD45(-)/VEGF-R2(+). To determine if the hemopoietic clusters are derived from endothelial cells, we tagged the E2 endothelial tree from the inside with low-density lipoproteins (LDL) coupled to DiI. 24 hours later, hemopoietic clusters were labelled by LDL. Since no CD45(+) cells were inserted among endothelial cells at the time of vascular labelling, hemopoietic clusters must be concluded to derive from precursors with an endothelial phenotype.
Asunto(s)
Aorta/embriología , Linaje de la Célula , Endotelio Vascular/embriología , Células Madre Hematopoyéticas/citología , Animales , Aorta/ultraestructura , Embrión de Pollo , Coturnix/embriología , Endotelio Vascular/ultraestructura , Hematopoyesis , Antígenos Comunes de Leucocito/aislamiento & purificación , Lipoproteínas LDL/aislamiento & purificación , Modelos Biológicos , Proteínas Tirosina Quinasas Receptoras/aislamiento & purificación , Receptores de Factores de Crecimiento/aislamiento & purificación , Receptores de Factores de Crecimiento Endotelial VascularRESUMEN
Recent advances in our understanding of blood cell development have included the identification of a hematopoietic progenitor derived from endothelial cells and the possibility that the embryonic and fetal environment can reprogram gene expression in adult hematopoietic stem cells.
Asunto(s)
Endotelio Vascular/citología , Células Madre Hematopoyéticas , Adulto , Animales , Hematopoyesis , HumanosRESUMEN
Two hemogenic sites are present in mouse embryos before the onset of fetal liver hemopoiesis. While the yolk sac provides for immediate erythropoiesis, an intraembryonic region encompassing the dorsal aorta produces definitive hematopoietic stem cells, as shown experimentally. At early developmental stages this region, that we named paraaortic splanchnopleura, produces multipotent progenitors. At the time of fetal liver colonisation, the paraaortic splanchnopleura further evolves into aorta, gonads and mesonephros (AGM) and contains progenitors capable of long term multilineage reconstitution. Only then are cytologically identifiable collections of early hemopoietic cells present in various arteries and in the mesentery. The present report focuses on the antigenic characterisation of immature hemopoietic progenitors in order to trace back the intraembryonic precursors at earlier developmental stages. CD34, an antigen expressed by immature progenitors and endothelial cells, labels all potential hemopoietic sites. Markers, supposed to counterstain endothelial cells and spare CD34+ hemopoietic cells, also stain various hemopoietic cells. The meaning of these shared antigenic expressions between cells of the endothelial and hemopoietic lineages in the early embryo is discussed.
Asunto(s)
Endotelio Vascular/citología , Células Madre Hematopoyéticas/inmunología , Animales , Antígenos CD34/análisis , Linaje de la Célula , Desarrollo Embrionario y Fetal , Endotelio Vascular/inmunología , Femenino , Células Madre Hematopoyéticas/citología , Hígado/citología , Hígado/embriología , Ratones , Ratones Endogámicos BALB C , Molécula-1 de Adhesión Celular Endotelial de Plaqueta/análisis , Conejos , Saco VitelinoRESUMEN
Until now the allantois has not been considered as a hematopoietic organ. Here we report experimental evidence demonstrating the in situ emergence of both hematopoietic and endothelial precursors in the avian allantoic bud. When the prevascularized allantoic bud from a quail embryo was grafted in the coelom of a chicken host, hematopoietic and endothelial cells later were found in the bone marrow of the host. Because the graft was located at a distance from the limb bud, these cells could reach the bone marrow only by the circulatory pathway. This blood-borne seeding may be accomplished by distinct hematopoietic and endothelial precursors, or by hemangioblasts, the postulated common precursors of these two lineages; we consider the latter interpretation more likely. We also show by reverse transcription-PCR that the allantois region expresses very early the GATA genes involved in hematopoiesis and some beta-globin chain genes.
Asunto(s)
Alantoides/citología , Proteínas de Unión al ADN/genética , Endotelio Vascular/embriología , Regulación del Desarrollo de la Expresión Génica , Hematopoyesis , Células Madre Hematopoyéticas/citología , Transactivadores/genética , Factores de Transcripción/genética , Animales , Médula Ósea/embriología , Embrión de Pollo , Quimera , Coturnix , Factores de Unión al ADN Específico de las Células Eritroides , Factor de Transcripción GATA2 , Factor de Transcripción GATA3 , Globinas/genéticaRESUMEN
Hemopoiesis, initiated in the early embryo yolk sac (YS) (7.5-8 days postcoitum (pc) in mouse), takes place thereafter in sites successively seeded by extrinsic hemopoietic stem cells (HSC). Since the existence of intraembryonic HSC has been proven experimentally in some vertebrates, it is also likely that not all HSC originate in the YS in mammals, as previously thought. Candidate intraembryonic sites that may be active in producing HSC before liver colonization are the para-aortic splanchnopleura (P-Sp) and the aorta-gonads-mesonephros region (AGM). Here we explore these sites directly for the presence of cells with hemopoietic-specific surface molecules and gene activities. The Ags c-kit, AA4.1, Mac-1, and Sca-1 begin to be expressed on some P-Sp and AGM cells, making it possible to distinguish subpopulations that evolve according to reproducible developmental patterns. On the basis of RAG-1 gene transcription, the first lymphoid precursors in the mouse embryo appear to be present 9.5 to 10 days pc in P-Sp/AGM and YS. Starting B-cell lymphopoiesis (9-12 days pc) is characterized by nonexpression of the surrogate light chain lambda 5-encoding gene and biased usage of IgH DJ4 rearrangements. In the 12.5- to 13.5-day-pc fetal liver (FL), a switch occurs, characterized by the random use of all IgH DJ and the detection of lambda 5 gene transcripts.
Asunto(s)
Antígenos de Superficie/genética , Regulación del Desarrollo de la Expresión Génica/inmunología , Células Madre Hematopoyéticas/inmunología , Subgrupos Linfocitarios/citología , Animales , Antígenos Ly/análisis , Antígenos de Superficie/análisis , Antígenos de Superficie/biosíntesis , Diferenciación Celular/genética , Diferenciación Celular/inmunología , Embrión de Mamíferos , Reordenamiento Génico de Linfocito B , Células Madre Hematopoyéticas/metabolismo , Cadenas Pesadas de Inmunoglobulina/genética , Cadenas J de Inmunoglobulina/genética , Región Variable de Inmunoglobulina/genética , Inmunofenotipificación , Subgrupos Linfocitarios/inmunología , Subgrupos Linfocitarios/metabolismo , Proteínas de la Membrana/análisis , Ratones , Ratones Endogámicos BALB CRESUMEN
Expression of the c-Ets1 protooncogene which codes for a transcription factor is associated with neovascularization and invasive processes. In order to determine c-Ets1 expression at the mRNA level, during the process of implantation during the first trimester of human pregnancy, samples of trophoblast were retrieved at the time of legal abortion and processed for in situ hybridization. We found that c-Ets1 mRNAs are transcribed in the endothelial cells of villous trophoblast and in the extravillous trophoblastic cells invading the uterine vessels. However, no transcript was found in maternal endothelial cells. We conclude that c-Ets1 plays a role in angiogenesis occurring in the development of the villous tree and is involved during the invasive process of the endometrium and maternal vessels by trophoblastic cells; this latter physiological event is crucial for a normal development of the fetus, its failure leading to pathological cases. We suggest that the role of the c-Ets1 protooncogene is related to the regulation of metalloproteinase genes transcription, a gene family which is known to be a target for Ets protein.