RESUMEN
Population aging is unprecedented, without parallel in human history, and the 21st century will witness even more rapid aging than did the century just past. Improvements in public health and medicine are having a profound effect on population demographics worldwide. By 2017, there will be more people over the age of 65 than under age 5, and by 2050, two billion of the estimated nine billion people on Earth will be older than 60 (http://unfpa.org/ageingreport/). Although we can reasonably expect to live longer today than past generations did, the age-related disease burden we will have to confront has not changed. With the proportion of older people among the global population being now higher than at any time in history and still expanding, maintaining health into old age (or healthspan) has become a new and urgent frontier for modern medicine. Geroscience is a cross-disciplinary field focused on understanding the relationships between the processes of aging and age-related chronic diseases. On October 30-31, 2013, the trans-National Institutes of Health GeroScience Interest Group hosted a Summit to promote collaborations between the aging and chronic disease research communities with the goal of developing innovative strategies to improve healthspan and reduce the burden of chronic disease.
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Envejecimiento , Investigación Biomédica/tendencias , Enfermedad Crónica/epidemiología , Geriatría/métodos , Esperanza de Vida/tendencias , Congresos como Asunto , Salud Global , Humanos , Morbilidad/tendenciasRESUMEN
The importance of the epicardium for myocardial and valvuloseptal development has been well established; perturbation of epicardial development results in cardiac abnormalities, including thinning of the ventricular myocardial wall and malformations of the atrioventricular valvuloseptal complex. To determine the spatiotemporal contribution of epicardially derived cells to the developing fibroblast population in the heart, we have used a mWt1/IRES/GFP-Cre mouse to trace the fate of EPDCs from embryonic day (ED)10 until birth. EPDCs begin to populate the compact ventricular myocardium around ED12. The migration of epicardially derived fibroblasts toward the interface between compact and trabecular myocardium is completed around ED14. Remarkably, epicardially derived fibroblasts do not migrate into the trabecular myocardium until after ED17. Migration of EPDCs into the atrioventricular cushion mesenchyme commences around ED12. As development progresses, the number of EPDCs increases significantly, specifically in the leaflets which derive from the lateral atrioventricular cushions. In these developing leaflets the epicardially derived fibroblasts eventually largely replace the endocardially derived cells. Importantly, the contribution of EPDCs to the leaflets derived from the major AV cushions is very limited. The differential contribution of EPDCs to the various leaflets of the atrioventricular valves provides a new paradigm in valve development and could lead to new insights into the pathogenesis of abnormalities that preferentially affect individual components of this region of the heart. The notion that there is a significant difference in the contribution of epicardially and endocardially derived cells to the individual leaflets of the atrioventricular valves has also important pragmatic consequences for the use of endocardial and epicardial cre-mouse models in studies of heart development.
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Fibroblastos/citología , Válvulas Cardíacas/embriología , Corazón/embriología , Pericardio/citología , Animales , Desarrollo Embrionario , Válvulas Cardíacas/citología , Ventrículos Cardíacos/citología , Ventrículos Cardíacos/embriología , Ratones , OrganogénesisRESUMEN
BACKGROUND: A third of all known freshwater mollusk extinctions worldwide have occurred within a single medium-sized American drainage. The Mobile River Basin (MRB) of Alabama, a global hotspot of temperate freshwater biodiversity, was intensively industrialized during the 20(th) century, driving 47 of its 139 endemic mollusk species to extinction. These include the ancylinid limpet Rhodacmea filosa, currently classified as extinct (IUCN Red List), a member of a critically endangered southeastern North American genus reduced to a single known extant population (of R. elatior) in the MRB. METHODOLOGY/PRINCIPAL FINDINGS: We document here the tripling of known extant populations of this North American limpet genus with the rediscovery of enduring Rhodacmea filosa in a MRB tributary and of R. elatior in its type locality: the Green River, Kentucky, an Ohio River Basin (ORB) tributary. Rhodacmea species are diagnosed using untested conchological traits and we reassessed their systematic and conservation status across both basins using morphometric and genetic characters. Our data corroborated the taxonomic validity of Rhodacmea filosa and we inferred a within-MRB cladogenic origin from a common ancestor bearing the R. elatior shell phenotype. The geographically-isolated MRB and ORB R. elatior populations formed a cryptic species complex: although overlapping morphometrically, they exhibited a pronounced phylogenetic disjunction that greatly exceeded that of within-MRB R. elatior and R. filosa sister species. CONCLUSIONS/SIGNIFICANCE: Rhodacmea filosa, the type species of the genus, is not extinct. It persists in a Coosa River tributary and morphometric and phylogenetic analyses confirm its taxonomic validity. All three surviving populations of the genus Rhodacmea merit specific status. They collectively contain all known survivors of a phylogenetically highly distinctive North American endemic genus and therefore represent a concentrated fraction of continental freshwater gastropod biodiversity. We recommend the establishment of a proactive targeted conservation program that may include their captive propagation and reintroduction.
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Extinción Biológica , Moluscos/anatomía & histología , Moluscos/genética , Animales , Moluscos/clasificación , Filogenia , Estados UnidosRESUMEN
RATIONALE: The proepicardium is a transient structure comprising epicardial progenitor cells located at the posterior limit of the embryonic cardiac inflow. A network of signals regulates proepicardial cell fate and defines myocardial and nonmyocardial domains at the venous pole of the heart. During cardiac development, epicardial-derived cells also contribute to coronary vessel morphogenesis. OBJECTIVE: To study Notch function during proepicardium development and coronary vessel formation in the mouse. METHODS AND RESULTS: Using in situ hybridization, RT-PCR, and immunohistochemistry, we find that Notch pathway elements are differentially activated throughout the proepicardial-epicardial-coronary transition. Analysis of RBPJk-targeted embryos indicates that Notch ablation causes ectopic procardiogenic signaling in the proepicardium that in turn promotes myocardial differentiation in adjacent mesodermal progenitors, resulting in a premature muscularization of the sinus venosus horns. Epicardium-specific Notch1 ablation using a Wt1-Cre driver line disrupts coronary artery differentiation, reduces myocardium wall thickness and myocyte proliferation, and reduces Raldh2 expression. Ectopic Notch1 activation disrupts epicardium development and causes thinning of ventricular walls. CONCLUSIONS: Epicardial Notch modulates cell differentiation in the proepicardium and adjacent pericardial mesoderm. Notch1 is later required for arterial endothelium commitment and differentiation and for vessel wall maturation during coronary vessel development and myocardium growth.
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Circulación Sanguínea/fisiología , Vasos Coronarios/embriología , Morfogénesis/fisiología , Pericardio/embriología , Receptores Notch/fisiología , Transducción de Señal/fisiología , Aldehído Oxidorreductasas/genética , Aldehído Oxidorreductasas/fisiología , Animales , Proteína Morfogenética Ósea 2/genética , Proteína Morfogenética Ósea 2/fisiología , Diferenciación Celular/fisiología , Proliferación Celular , Vasos Coronarios/citología , Proteína de Unión a la Señal Recombinante J de las Inmunoglobulinas/genética , Proteína de Unión a la Señal Recombinante J de las Inmunoglobulinas/fisiología , Ratones , Ratones Endogámicos , Ratones Transgénicos , Modelos Animales , Mutación , Pericardio/citología , Receptor Notch1/genética , Receptor Notch1/fisiología , Receptores Notch/genéticaRESUMEN
AIMS: During development, the heart tube grows by differentiation of Isl1(+)/Nkx2-5(+) progenitors to the arterial and venous pole and dorsal mesocardium. However, after the establishment of the heart tube, Tbx18(+) progenitors were proposed to form the Tbx18(+)/Nkx2-5(-) sinus venosus and proepicardium. To elucidate the relationship between these contributions, we investigated the origin of the Tbx18(+) sinus venosus progenitor population in the cardiogenic mesoderm and its spatial and temporal relation to the second heart field during murine heart development. METHODS AND RESULTS: Explant culture revealed that the Tbx18(+) cell population has the potential to form Nkx2-5(-) sinus venosus myocardium. Three-dimensional reconstruction of expression patterns showed that during heart tube elongation, the Tbx18(+) progenitors remained spatially and temporally separate from the Isl1(+) second heart field, only overlapping with the Isl1(+) domain at the right lateral side of the inflow tract, where the sinus node developed. Consistently, genetic lineage analysis revealed that the Tbx18(+) descendants formed the sinus venosus myocardium, but did not contribute to the pulmonary vein myocardium that developed in the Isl1(+) second heart field. By means of DiI labelling and expression analysis, the origin of the sinus venosus progenitor population was traced to the lateral rim of splanchnic mesoderm that down-regulated Nkx2-5 expression approximately 2 days before its differentiation into sinus venosus myocardium. CONCLUSION: Our data indicate that the cardiogenic mesoderm contains an additional progenitor subpopulation that contributes to the sinus venosus myocardium. After patterning of the cardiogenic mesoderm, this progenitor population remains spatially separated and genetically distinctive from the second heart field subpopulation.
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Corazón/embriología , Mesodermo/metabolismo , Miocitos Cardíacos/metabolismo , Células Madre/metabolismo , Animales , Diferenciación Celular , Linaje de la Célula , Movimiento Celular , Edad Gestacional , Proteínas Fluorescentes Verdes/genética , Proteínas Fluorescentes Verdes/metabolismo , Proteína Homeótica Nkx-2.5 , Proteínas de Homeodominio/metabolismo , Proteínas con Homeodominio LIM , Operón Lac/genética , Mesodermo/citología , Ratones , Ratones Transgénicos , Morfogénesis , Proteínas/genética , Venas Pulmonares/embriología , Venas Pulmonares/metabolismo , ARN no Traducido , Proteínas Recombinantes de Fusión/metabolismo , Nodo Sinoatrial/embriología , Nodo Sinoatrial/metabolismo , Proteínas de Dominio T Box/genética , Proteínas de Dominio T Box/metabolismo , Técnicas de Cultivo de Tejidos , Factores de Transcripción/metabolismoRESUMEN
BACKGROUND: The mass extirpation of the island of Moorea's endemic partulid tree snail fauna, following the deliberate introduction of the alien predator Euglandina rosea, represents one of the highest profile conservation crises of the past thirty years. All of the island's partulids were thought to be extirpated by 1987, with five species persisting in zoos, but intensive field surveys have recently detected a number of surviving wild populations. We report here a mitochondrial (mt) phylogenetic estimate of Moorean partulid wild and captive lineage survival calibrated with a reference museum collection that pre-dates the predator's introduction and that also includes a parallel dataset from the neighboring island of Tahiti. RESULTS: Although severe winnowing of Moorea's mt lineage diversity has occurred, seven of eight (six Partula; two Samoana) partulid tip clades remain extant. The extinct mt clade occurred predominantly in the P. suturalis species complex and it represented a major component of Moorea's endemic partulid treespace. Extant Moorean mt clades exhibited a complex spectrum of persistence on Moorea, in captivity, and (in the form of five phylogenetically distinct sister lineages) on Tahiti. Most notably, three Partula taxa, bearing two multi-island mt lineages, have survived decades of E. rosea predation on Moorea (P. taeniata) and in the valleys of Tahiti (P. hyalina and P. clara). Their differential persistence was correlated with intrinsic attributes, such as taxonomy and mt lineages, rather than with their respective within-island distribution patterns. CONCLUSION: Conservation efforts directed toward Moorean and Tahitian partulids have typically operated within a single island frame of reference, but our discovery of robust genealogical ties among survivors on both islands implies that a multi-island perspective is required. Understanding what genetic and/or ecological factors have enabled Partula taeniata, P. hyalina and P. clara to differentially survive long-term direct exposure to the predator may provide important clues toward developing a viable long term conservation plan for Society Island partulid tree snails.
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Conservación de los Recursos Naturales , Extinción Biológica , Filogenia , Caracoles/genética , Animales , ADN Mitocondrial/genética , Variación Genética , Geografía , Polinesia , Análisis de Secuencia de ADN , Caracoles/clasificaciónRESUMEN
BACKGROUND: The atrioventricular (AV) node is essential for the sequential excitation and optimized contraction of the adult multichambered heart; however, relatively little is known about its formation from the embryonic AV canal. A recent study demonstrated that signaling by Alk3, the type 1a receptor for bone morphogenetic proteins, in the myocardium of the AV canal was required for the development of both the AV valves and annulus fibrosus. To test the hypothesis that bone morphogenetic protein signaling also plays a role in AV node formation, we investigated conduction system function and AV node morphology in adult mice with conditional deletion of Alk3 in the AV canal. METHODS AND RESULTS: High-resolution optical mapping with correlative histological analysis of 28 mutant hearts revealed 4 basic phenotypic classes based on electrical activation patterns and volume-conducted ECGs. The frequency of AV node conduction and morphological abnormalities increased from no detectable anomalies (class I) to severe defects (class IV), which included the presence of bypass tracts, abnormal ventricular activation patterns, fibrosis of the AV node, and twin AV nodes. CONCLUSIONS: The present findings demonstrate that bone morphogenetic protein signaling is required in the myocardium of the AV canal for proper AV junction development, including the AV node.
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Nodo Atrioventricular/fisiopatología , Mapeo del Potencial de Superficie Corporal , Receptores de Proteínas Morfogenéticas Óseas de Tipo 1/genética , Sistema de Conducción Cardíaco/fisiopatología , Animales , Nodo Atrioventricular/crecimiento & desarrollo , Receptores de Proteínas Morfogenéticas Óseas de Tipo 1/deficiencia , Receptores de Proteínas Morfogenéticas Óseas de Tipo 1/fisiología , Genotipo , Bloqueo Cardíaco , Ratones , Ratones Mutantes , Miocardio/patologíaRESUMEN
Inter-archipelago exchange networks were an important aspect of prehistoric Polynesian societies. We report here a novel genetic characterization of a prehistoric exchange network involving an endemic Pacific island tree snail, Partula hyalina. It occurs in the Society (Tahiti only), Austral and Southern Cook Islands. Our genetic data, based on museum, captive and wild-caught samples, establish Tahiti as the source island. The source lineage is polymorphic in shell coloration and contains a second nominal species, the dark-shelled Partula clara, in addition to the white-shelled P. hyalina. Prehistoric inter-island introductions were non-random: they involved white-shelled snails only and were exclusively inter-archipelago in scope. Partulid shells were commonly used in regional Polynesian jewellery, and we propose that the white-shelled P. hyalina, originally restricted to Tahiti, had aesthetic value throughout these archipelagoes. Demand within the Society Islands could be best met by trading dead shells, but a low rate of inter-archipelago exchange may have prompted the establishment of multiple founder populations in the Australs and Southern Cooks. The alien carnivorous land snail Euglandina rosea has recently devastated populations of all 61 endemic species of Society Island partulid snails. Southern Cooks and Australs P. hyalina now represent the only unscathed wild populations remaining of this once spectacular land snail radiation.
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Conservación de los Recursos Naturales , Caracoles/clasificación , Animales , Comercio , ADN Mitocondrial/química , Haplotipos , Humanos , Funciones de Verosimilitud , Polinesia , Caracoles/genética , Conducta SocialRESUMEN
Oceanic islands frequently support endemic faunal radiations that are highly vulnerable to introduced predators [1]. This vulnerability is epitomized by the rapid extinction in the wild of all but five of 61 described Society Islands partulid tree snails [2], following the deliberate introduction of an alien biological control agent: the carnivorous snail Euglandina rosea[3]. Tahiti's tree snail populations have been almost completely extirpated and three of the island's eight endemic Partula species are officially extinct, a fourth persisting only in captivity [2]. We report a molecular phylogenetic estimate of Tahitian Partula mitochondrial lineage survival calibrated with a 1970 reference museum collection that pre-dates the predator's 1974 introduction to the island [4]. Although severe winnowing of lineage diversity has occurred, none of the five primary Tahitian Partula clades present in the museum samples is extinct. Targeted conservation measures, especially of montane refuge populations, may yet preserve a representative sub-sample of Tahiti's endemic tree snail genetic diversity in the wild.
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ADN Mitocondrial , Filogenia , Caracoles/genética , Animales , Extinción Biológica , Geografía , PolinesiaRESUMEN
Periostin is a fasciclin-containing adhesive glycoprotein that facilitates the migration and differentiation of cells that have undergone epithelial-mesenchymal transformation during embryogenesis and in pathological conditions. Despite the importance of post-transformational differentiation as a general developmental mechanism, little is known how periostin's embryonic expression is regulated. To help resolve this deficiency, a 3.9-kb periostin proximal promoter was isolated and shown to drive tissue-specific expression in the neural crest-derived Schwann cell lineage and in a subpopulation of periostin-expressing cells in the cardiac outflow tract endocardial cushions. In order to identify the enhancer and associated DNA binding factor(s) responsible, in vitro promoter dissection was undertaken in a Schwannoma line. Ultimately a 304-bp(peri) enhancer was identified and shown to be capable of recapitulating 3.9 kb(peri-lacZ)in vivo spatiotemporal patterns. Further mutational and EMSA analysis helped identify a minimal 37-bp region that is bound by the YY1 transcription factor. The 37-bp enhancer was subsequently shown to be essential for in vivo 3.9 kb(peri-lacZ) promoter activity. Taken together, these studies identify an evolutionary-conserved YY1-binding 37-bp region within a 304-bp periostin core enhancer that is capable of regulating simultaneous novel tissue-specific periostin expression in the cardiac outflow-tract cushion mesenchyme and Schwann cell lineages.
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Moléculas de Adhesión Celular/genética , Endocardio/embriología , Endocardio/metabolismo , Elementos de Facilitación Genéticos , Células de Schwann/metabolismo , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Sitios de Unión/genética , Moléculas de Adhesión Celular/química , Moléculas de Adhesión Celular/metabolismo , Línea Celular , Secuencia Conservada , Sondas de ADN/genética , Endocardio/citología , Corazón Fetal/citología , Corazón Fetal/embriología , Corazón Fetal/metabolismo , Regulación del Desarrollo de la Expresión Génica , Genes Reporteros , Operón Lac , Ratones , Ratones Endogámicos C57BL , Ratones Transgénicos , Datos de Secuencia Molecular , Mutagénesis Sitio-Dirigida , Regiones Promotoras Genéticas , Células de Schwann/citología , Eliminación de Secuencia , Homología de Secuencia de Aminoácido , Factor de Transcripción YY1/metabolismoRESUMEN
Apoptosis occurs at high frequency in the myocardium of the developing avian cardiac outflow tract (OFT). Up- or down-regulating apoptosis results in defects resembling human conotruncal heart anomalies. This finding suggested that regulated levels of apoptosis are critical for normal morphogenesis of the four-chambered heart. Recent evidence supports an important role for hypoxia of the OFT myocardium in regulating cell death and vasculogenesis. The purpose of this study was to determine whether apoptosis in the outflow tract myocardium occurs in the mouse heart during developmental stages comparable to the avian heart and to determine whether differential hypoxia is also present at this site in the murine heart. Apoptosis was detected using a fluorescent vital dye, Lysotracker Red (LTR), in the OFT myocardium of the mouse starting at embryonic day (E) 12.5, peaking at E13.5-14.5, and declining thereafter to low or background levels by E18.5. In addition, high levels of apoptosis were detected in other cardiac regions, including the apices of the ventricles and along the interventricular sulcus. Apoptosis in the myocardium was detected by double-labeling with LTR and cardiomyocyte markers. Terminal deoxynucleotidyl transferase-mediated deoxyuridinetriphosphate nick end-labeling (TUNEL) and immunostaining for cleaved Caspase-3 were used to confirm the LTR results. At the peak of OFT apoptosis in the mouse, the OFT myocardium was relatively hypoxic, as indicated by specific and intense EF5 staining and HIF1alpha nuclear localization, and was surrounded by the developing vasculature as in the chicken embryo. These findings suggest that cardiomyocyte apoptosis is an evolutionarily conserved mechanism for normal morphogenesis of the outflow tract myocardium in avian and mammalian species.
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Apoptosis , Corazón Fetal/citología , Animales , Caspasa 3 , Caspasas/metabolismo , Embrión de Pollo , Femenino , Corazón Fetal/metabolismo , Edad Gestacional , Corazón/embriología , Humanos , Hipoxia/metabolismo , Etiquetado Corte-Fin in Situ , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Transgénicos , Embarazo , Especificidad de la Especie , Coloración y EtiquetadoRESUMEN
The North American freshwater limpet genus Laevapex (Walker, 1903) is a ubiquitous inhabitant of lentic and slow-moving lotic habitats east of the Rocky Mountains, but uncertainty clouds its systematic affinities, the phylogenetic validity of its constituent nominal species, and its degree of genetic connectivity among drainages. We addressed these issues by sampling the genus throughout much of its collective range and constructing representative nuclear and mitochondrial (mt) gene trees, in addition to performing morphometric analyses of shell shape variation. Our results identify neotropical Gundlachia and South American Uncancylus as sister lineages for Laevapex and reveal a pronounced sub-familial dichotomy within the Ancylidae, separating these three New World genera from a Holarctic (Ferrissia (Ancylus, Rhodacmea)) sister clade. Five nominal taxa (L. fuscus, L. diaphanus, L. peninsulae, L. sp., and "F."arkansasensis), indistinguishable in our morphometric analyses, were polyphyletic in the mt gene trees, exhibited modest levels (< 3.9%) of genetic divergence in the primary (103 of 109 individuals) mt clade and, with one minor exception, they appeared fixed for a single nuclear ITS-2 genotype. Although complicated by the presence of rare, highly divergent mt lineages (of either introgressive or persistent ancestral polymorphic origin) in some populations, the molecular data were consistent with a taxonomic conclusion that these five nominal taxa represent a single polymorphic lineage of the type species L. fuscus. AMOVA analyses indicated that 56% of the observed mt variation could be attributed to among population differences, only two of 36 haplotypes were detected in more than one sampling location, and estimates of among-population mt gene flow were generally low at both regional and continental scales. Unrooted network analyses revealed a number of mt tip clades, one restricted to the southwestern part of the range, the remainder having overlapping distributions in eastern North America. All of the eastern tip clades occurred in the Mid-Atlantic region, and these samples displayed by far the highest levels of collective mt diversity. However, directional gene flow estimates indicated that this region has been a recipient (especially from Alabama populations), rather than a source of haplotypic diversity, implying that it likely represents a center of overlap, not a primary ice age refugium, for this limpet species.
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Agua Dulce , Gastrópodos/genética , Filogenia , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Canadá , ADN Ribosómico/genética , Gastrópodos/anatomía & histología , Gastrópodos/química , Gastrópodos/clasificación , Genotipo , Haplotipos/genética , Datos de Secuencia Molecular , Alineación de Secuencia , Estados UnidosRESUMEN
Since rates of cardiomyocyte generation in the embryo are much higher than within the adult, we explored whether the embryonic heart would serve as useful experimental system for examining the myocardial potential of adult stem cells. Previously, we reported that the long-term culturing of adult mouse bone marrow produced a cell population that was both highly enriched for macrophages and cardiac competent. In this study, the myocardial potential of this cell population was analyzed in greater detail using the embryonic chick heart as recipient tissue. Experiments involving the co-incubation of labeled bone marrow cells with embryonic heart tissue showed that bone marrow (BM) cells incorporated into the myocardium and immunostained for myocyte proteins. Reverse transcription-polymerase chain reaction analysis demonstrated that the heart tissue induced bone marrow cells to express the differentiated cardiomyocyte marker alpha-cardiac myosin heavy chain. The cardiomyocyte conversion of the bone marrow cells was verified by harvesting donor cells from mice that were genetically labeled with a myocardial-specific beta-galactosidase reporter. Embryonic hearts exposed to the transgenic bone marrow in culture exhibited significant numbers of beta-galactosidase-positive cells, indicating the presence of bone marrow-derived cells that had converted to a myocardial phenotype. Furthermore, when transgenic mouse BM cells were injected into living chick embryos, donor cells incorporated into the developing heart and exhibited a myocardial phenotype. Immunofluorescence analysis demonstrated that donor BM cells exhibiting myocyte markers contained only nuclei from mouse cells, indicating that differentiation and not cell fusion was the predominant mechanism for the acquisition of a myocyte phenotype. These data confirm that adult mouse bone marrow contain cells with the ability to form cardiomyocytes. In addition, the predominance of the macrophage phenotype within the donor bone marrow cell population suggests that transdifferentiation of immune response cells may play a role in cellular regeneration in the adult.
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Células de la Médula Ósea/citología , Diferenciación Celular/fisiología , Proliferación Celular , Corazón/embriología , Miocardio/citología , Miocitos Cardíacos/citología , Animales , Trasplante de Médula Ósea , Embrión de Pollo , Medios de Cultivo Condicionados , Expresión Génica , Proteínas Fluorescentes Verdes/genética , Proteínas Fluorescentes Verdes/metabolismo , Macrófagos/citología , Ratones , Ratones Transgénicos , Trasplante HeterólogoRESUMEN
Most internal organs are situated in a coelomic cavity and are covered by a mesothelium. During heart development, epicardial cells (a mesothelium) move to and over the heart, undergo epithelial-mesenchymal transition (EMT), and subsequently differentiate into endothelial and vascular smooth muscle cells. This is thought to be a unique process in blood vessel formation. Still, structural and developmental similarities between the heart and gut led us to test the hypothesis that a conserved or related mechanism may regulate blood vessel development to the gut, which, similar to the heart, is housed in a coelomic cavity. By using a combination of molecular genetics, vital dye fate mapping, organ culture and immunohistochemistry, we demonstrate that the serosal mesothelium is the major source of vasculogenic cells in developing mouse gut. Our studies show that the gut is initially devoid of a mesothelium but that serosal mesothelial cells expressing the Wilm's tumor protein (Wt1) move to and over the gut. Subsequently, a subset of these cells undergoes EMT and migrates throughout the gut. Using Wt1-Cre genetic lineage marking of serosal cells and their progeny, we demonstrate that these cells differentiate to smooth muscle of all major blood vessels in the mesenteries and gut. Our data reveal a conserved mechanism in blood vessel formation to coelomic organs, and have major implications for our understanding of vertebrate organogenesis and vascular deficiencies of the gut.
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Inducción Embrionaria , Epitelio/fisiología , Intestinos/irrigación sanguínea , Miocitos del Músculo Liso/citología , Membrana Serosa/citología , Animales , Biomarcadores/análisis , Vasos Sanguíneos/embriología , Vasos Sanguíneos/crecimiento & desarrollo , Desarrollo Embrionario , Células Epiteliales/citología , Células Epiteliales/fisiología , Intestinos/embriología , Ratones , Ratones Transgénicos , Músculo Liso Vascular/citología , Organogénesis , Proteínas WT1/análisisRESUMEN
Endocardial cushions are precursors of mature atrioventricular (AV) valves. Their formation is induced by signaling molecules originating from the AV myocardium, including bone morphogenetic proteins (BMPs). Here, we hypothesized that BMP signaling plays an important role in the AV myocardium during the maturation of AV valves from the cushions. To test our hypothesis, we used a unique Cre/lox system to target the deletion of a floxed Alk3 allele, the type IA receptor for BMPs, to cardiac myocytes of the AV canal (AVC). Lineage analysis indicated that cardiac myocytes of the AVC contributed to the tricuspid mural and posterior leaflets, the mitral septal leaflet, and the atrial border of the annulus fibrosus. When Alk3 was deleted in these cells, defects were seen in the same leaflets, ie, the tricuspid mural leaflet and mitral septal leaflet were longer, the tricuspid posterior leaflet was displaced and adherent to the ventricular wall, and the annulus fibrosus was disrupted resulting in ventricular preexcitation. The defects seen in mice with AVC-targeted deletion of Alk3 provide strong support for a role of Alk3 in human congenital heart diseases, such as Ebstein's anomaly. In conclusion, our mouse model demonstrated critical roles for Alk3 signaling in the AV myocardium during the development of AV valves and the annulus fibrosus.
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Válvulas Cardíacas/embriología , Corazón/embriología , Proteínas Serina-Treonina Quinasas/fisiología , Receptores de Factores de Crecimiento/fisiología , Animales , Receptores de Proteínas Morfogenéticas Óseas de Tipo 1 , Proteínas de Unión al ADN/genética , Factor de Transcripción GATA6 , Válvulas Cardíacas/anomalías , Integrasas/genética , Ratones , Ratones Transgénicos , Miocitos Cardíacos/fisiología , Transducción de Señal , Factores de Transcripción/genéticaRESUMEN
GATA factors regulate critical events in hematopoietic lineages (GATA-1/2/3), the heart and gut (GATA-4/5/6) and various other tissues. Transgenic approaches have revealed that GATA genes are regulated in a modular fashion by sets of enhancers that govern distinct temporal and/or spatial facets of the overall expression patterns. Efforts are underway to resolve how these GATA gene enhancers are themselves regulated in order to elucidate the genetic and molecular hierarchies that govern GATA expression in particular developmental contexts. These enhancers also afford a raft of tools that can be used to selectively perturb and probe various developmental events in transgenic animals.
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Proteínas de Unión al ADN/genética , Regulación del Desarrollo de la Expresión Génica , Factores de Transcripción/genética , Vertebrados/crecimiento & desarrollo , Animales , Proteínas de Unión al ADN/metabolismo , Elementos de Facilitación Genéticos , Factores de Unión al ADN Específico de las Células Eritroides , Peces/crecimiento & desarrollo , Factor de Transcripción GATA2 , Factor de Transcripción GATA3 , Factor de Transcripción GATA4 , Factor de Transcripción GATA5 , Factor de Transcripción GATA6 , Corazón/crecimiento & desarrollo , Intestinos/crecimiento & desarrollo , Transactivadores/genética , Factores de Transcripción/metabolismo , Vertebrados/metabolismoRESUMEN
During folding of the embryo, lateroanterior visceral mesoderm forms the embryonic tubular heart at the midline, just ventral to the foregut. In mice, this nascent tube contains the future left ventricle and atrioventricular canal. Mesenchymal cells subsequently recruited to the cardiac lineage at the intake and the outflow of the tube will form the atria and the right ventricle and outflow tract, respectively. Shortly after its emergence, the embryonic heart tube starts to loop, and the first signs of left ventricular chamber differentiation become visible on the outer curvature of the middle portion of the tube. Subsequently, the right ventricle differentiates cranially, and the atria caudally, while the inflow tract, atrioventricular canal, inner curvatures, and outflow tract form recognizable components flanking the chambers. The latter, nonchamber regions in turn provide signals for the formation of the cushion mesenchyme, are involved in remodeling of the heart, and form the nodes of the conduction system. This review discusses how the patterning of the heart tube relates to the localized differentiation of atrial and ventricular chambers, why some parts of the heart do not form chambers, and how this relates to the formation of the conduction system.
Asunto(s)
Expresión Génica , Corazón/embriología , Ratones/embriología , Morfogénesis/genética , Animales , Atrios Cardíacos/embriología , Sistema de Conducción Cardíaco/embriología , Ventrículos Cardíacos/embriología , Humanos , Células Madre Mesenquimatosas , Morfogénesis/fisiología , Miocitos CardíacosRESUMEN
The cGATA-6 gene is flanked by an enhancer that selectively marks the atrioventricular conduction system (AVCS) in transgenic mice. This enhancer reads anterior/posterior and medial/lateral positional information very early in the cardiogenic program and remains active in progressively more restricted regions of primary myocardium leading up to the emergence of a histologically distinct AVCS. We undertook to parse this enhancer to resolve how the respective AVCS-specific transcription program is regulated at the molecular level. We determined that this AVCS enhancer includes a 102 bp module that is sufficient to restrict expression to primary nonchamber myocardium. This offers a novel tool to analyze the early molecular delineation of primary and chamber myocardium, which subsequently give rise to components of the central and peripheral conduction system, respectively. Furthermore, we show that this 102 bp module in turn contains a nested 47 bp core module that has the potential to direct expression specifically to the AVCS domain of primary myocardium, albeit with low efficiency. Accordingly, we show that a GATA site and a GC-rich site in the 102 bp region bolster the activity of the nested 47 bp AVCS core region even within the context of the parental 1,478 bp enhancer. These are the first functional elements to be reported for a cardiac conduction system-specific control region.
Asunto(s)
Nodo Atrioventricular/efectos de los fármacos , Proteínas de Unión al ADN/fisiología , Elementos de Facilitación Genéticos , Genes Reguladores , Miocardio/metabolismo , Factores de Transcripción/fisiología , Animales , Nodo Atrioventricular/embriología , Secuencia de Bases , Proteínas de Unión al ADN/genética , Ensayo de Cambio de Movilidad Electroforética , Factor de Transcripción GATA6 , Ratones , Ratones Transgénicos , Datos de Secuencia Molecular , Miocardio/citología , Regiones Promotoras Genéticas/genética , Factores de Transcripción/genética , Dedos de ZincRESUMEN
The mouse is the animal of choice for the study of molecular mechanisms involved in the regulation of cardiovascular morphogenesis and function. Recently, a series of genetically engineered mouse models have been reported (e.g. cGATA6/lacZ, MinK/lacZ knock-in/knock-out, engrailed2/lacZ, Cardiac troponin I/lacZ) that provide new and exciting information on the development of the atrioventricular conduction system (AVCS). On the basis of these and ongoing studies, concepts for the formation of the AVCS are continuously being adjusted. A proper understanding of the normal developmental mechanisms underlying the cardiac remodelling leading to the formation of the AVCS is imperative for the interpretation of cardiac abnormalities, including conduction disturbances, as observed in some genetically perturbed (knockout) mice. In this paper information on murine AVCS development will be integrated with published and unpublished results from studies in other vertebrates, including human and rabbit. We will illustrate that although many pieces of the puzzle still remain to be gathered, the outline of a very complex and critical event in cardiac morphogenesis is slowly emerging. Specifically, we will re-evaluate the concept of the 'primary ring' in the context of the new insights in the development of the AV junction as provided by the respective mouse models described above.