RESUMEN
The first site exhibiting hematopoietic activity in mammalian development is the yolk-sac blood island, which originates from the hemangioblast. Here we performed differentiation assays, as well as genome-wide molecular and functional studies in blast colony-forming cells to gain insight into the function of the essential Ldb1 factor in early primitive hematopoietic development. We show that the previously reported lack of yolk-sac hematopoiesis and vascular development in Ldb1(-/-) mouse result from a decreased number of hemangioblasts and a block in their ability to differentiate into erythroid and endothelial progenitor cells. Transcriptome analysis and correlation with the genome-wide binding pattern of Ldb1 in hemangioblasts revealed a number of direct-target genes and pathways misregulated in the absence of Ldb1. The regulation of essential developmental factors by Ldb1 defines it as an upstream transcriptional regulator of hematopoietic/endothelial development. We show the complex interplay that exists between transcription factors and signaling pathways during the very early stages of hematopoietic/endothelial development and the specific signaling occurring in hemangioblasts in contrast to more advanced hematopoietic developmental stages. Finally, by revealing novel genes and pathways not previously associated with early development, our study provides novel candidate targets to manipulate the differentiation of hematopoietic and/or endothelial cells.
Asunto(s)
Proteínas de Unión al ADN/genética , Hematopoyesis/genética , Proteínas con Dominio LIM/genética , Transducción de Señal/genética , Saco Vitelino/metabolismo , Animales , Diferenciación Celular/genética , Proteínas de Unión al ADN/metabolismo , Células Madre Embrionarias/citología , Células Madre Embrionarias/metabolismo , Perfilación de la Expresión Génica , Regulación del Desarrollo de la Expresión Génica , Genoma/genética , Hemangioblastos/citología , Hemangioblastos/metabolismo , Sistema Hematopoyético/irrigación sanguínea , Sistema Hematopoyético/embriología , Sistema Hematopoyético/metabolismo , Proteínas con Dominio LIM/metabolismo , Ratones , Ratones Noqueados , Análisis de Secuencia por Matrices de Oligonucleótidos , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Saco Vitelino/irrigación sanguínea , Saco Vitelino/embriologíaRESUMEN
Genome-wide chromatin profiling efforts have shown that enhancers are often located at large distances from gene promoters within the noncoding genome. Whereas enhancers can stimulate transcription initiation by communicating with promoters via chromatin looping mechanisms, we propose that enhancers may also stimulate transcription elongation by physical interactions with intronic elements. We review here recent findings derived from the study of the hematopoietic system.
Asunto(s)
Elementos de Facilitación Genéticos , Regulación de la Expresión Génica , Transcripción Genética , Animales , Ensamble y Desensamble de Cromatina , Genoma , Humanos , Elongación de la Transcripción GenéticaRESUMEN
RUNX1 is known to be an essential transcription factor for generating hematopoietic stem cells (HSC), but much less is known about its role in the downstream process of hematopoietic differentiation. RUNX1 has been shown to be part of a large transcription factor complex, together with LDB1, GATA1, TAL1, and ETO2 (N. Meier et al., Development 133:4913-4923, 2006) in erythroid cells. We used a tagging strategy to show that RUNX1 interacts with two novel protein partners, LSD1 and MYEF2, in erythroid cells. MYEF2 is bound in undifferentiated cells and is lost upon differentiation, whereas LSD1 is bound in differentiated cells. Chromatin immunoprecipitation followed by sequencing (ChIP-seq) and microarray expression analysis were used to show that RUNX1 binds approximately 9,000 target sites in erythroid cells and is primarily active in the undifferentiated state. Functional analysis shows that a subset of the target genes is suppressed by RUNX1 via the newly identified partner MYEF2. Knockdown of Myef2 expression in developing zebrafish results in a reduced number of HSC.
Asunto(s)
Subunidad alfa 2 del Factor de Unión al Sitio Principal/metabolismo , Células Eritroides/metabolismo , Regulación del Desarrollo de la Expresión Génica , Hematopoyesis , Complejos Multiproteicos/metabolismo , Proteínas del Tejido Nervioso/metabolismo , Oxidorreductasas N-Desmetilantes/metabolismo , Proteínas Represoras/metabolismo , Proteínas de Pez Cebra/metabolismo , Animales , Línea Celular Tumoral , Subunidad alfa 2 del Factor de Unión al Sitio Principal/genética , ADN/metabolismo , Técnicas de Silenciamiento del Gen , Histona Demetilasas , Ratones , Morfolinos/administración & dosificación , Morfolinos/genética , Proteínas del Tejido Nervioso/genética , Unión Proteica , Proteínas Represoras/genética , Pez Cebra/embriología , Proteínas de Pez Cebra/genéticaRESUMEN
Hematopoietic stem cells (HSCs) are responsible for the life-long production of the blood system and are pivotal cells in hematologic transplantation therapies. During mouse and human development, the first HSCs are produced in the aorta-gonad-mesonephros region. Subsequent to this emergence, HSCs are found in other anatomical sites of the mouse conceptus. While the mouse placenta contains abundant HSCs at midgestation, little is known concerning whether HSCs or hematopoietic progenitors are present and supported in the human placenta during development. In this study we show, over a range of developmental times including term, that the human placenta contains hematopoietic progenitors and HSCs. Moreover, stromal cell lines generated from human placenta at several developmental time points are pericyte-like cells and support human hematopoiesis. Immunostaining of placenta sections during development localizes hematopoietic cells in close contact with pericytes/perivascular cells. Thus, the human placenta is a potent hematopoietic niche throughout development.