RESUMO
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.
Assuntos
Proteínas de Ligação a DNA/genética , Hematopoese/genética , Proteínas com Domínio LIM/genética , Transdução de Sinais/genética , Saco Vitelino/metabolismo , Animais , Diferenciação Celular/genética , Proteínas de Ligação a DNA/metabolismo , Células-Tronco Embrionárias/citologia , Células-Tronco Embrionárias/metabolismo , Perfilação da Expressão Gênica , Regulação da Expressão Gênica no Desenvolvimento , Genoma/genética , Hemangioblastos/citologia , Hemangioblastos/metabolismo , Sistema Hematopoético/irrigação sanguínea , Sistema Hematopoético/embriologia , Sistema Hematopoético/metabolismo , Proteínas com Domínio LIM/metabolismo , Camundongos , Camundongos Knockout , Análise de Sequência com Séries de Oligonucleotídeos , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Saco Vitelino/irrigação sanguínea , Saco Vitelino/embriologiaRESUMO
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Assuntos
Humanos , Criança , Pediatria/ética , Pediatria/legislação & jurisprudência , Cordão Umbilical , Sangue Fetal/transplante , Sistema Hematopoético/irrigação sanguínea , Neutrófilos/transplante , Doadores não Relacionados/ética , Doadores não Relacionados/legislação & jurisprudênciaRESUMO
The first step in the homing of hematopoietic progenitor cells (HPCs) from the peripheral blood to the bone marrow involves an adhesion molecule-dependent contact with human bone marrow endothelial cells (HBMECs). In the present study we describe the constitutive expression of two of these molecules, E-selectin and vascular cell adhesion molecule-1 (VCAM-1), on endothelial cells of hematopoietic tissues. Immunophenotypic analysis of tissue sections of hematopoietically active (human adult and fetal bone marrow, fetal spleen, fetal liver, and adult spleen with extramedullary hematopoiesis) and inactive tissues (human adult spleen, lymph node, appendix, and liver; and fetal lung and fetal intestine) revealed that E-selectin and VCAM-1 are selectively expressed on endothelial cells of adult and fetal hematopoietic organs. These results were validated by means of reverse-transcriptase polymerase chain reaction. Adhesion studies revealed that binding of normal mobilized peripheral blood HPCs to HBMECs was completely inhibited by preincubation of HBMECs with anti-E-selectin (ENA2), whereas no effect of anti-VCAM-1 (1G11B1) was detected. These results suggest that E-selectin plays a role in the homing of HPCs and that its constitutive expression on endothelial cells of hematopoietic organs may be essential in the initial step of the homing process.
