title: The notch ligand delta-like 4 regulates multiple stages of early hemato-vascular development.
abstract: BACKGROUND
  In mouse embryos, homozygous or heterozygous deletions of the gene encoding the Notch ligand Dll4 result in early embryonic death due to major defects in endothelial remodeling in the yolk sac and embryo. Considering the close developmental relationship between endothelial and hematopoietic cell lineages, which share a common mesoderm-derived precursor, the hemangioblast, and many key regulatory molecules, we investigated whether Dll4 is also involved in the regulation of early embryonic hematopoiesis.
  
  
  RESULTS
  Using Embryoid Bodies (EBs) derived from embryonic stem cells harboring hetero- or homozygous Dll4 deletions, we observed that EBs from both genotypes exhibit an abnormal endothelial remodeling in the vascular sprouts that arise late during EB differentiation, indicating that this in vitro system recapitulates the angiogenic phenotype of Dll4 mutant embryos. However, analysis of EB development at early time points revealed that the absence of Dll4 delays the emergence of mesoderm and severely reduces the number of blast-colony forming cells (BL-CFCs), the in vitro counterpart of the hemangioblast, and of endothelial cells. Analysis of colony forming units (CFU) in EBs and yolk sacs from Dll4(+/-) and Dll4(-/-) embryos, showed that primitive erythropoiesis is specifically affected by Dll4 insufficiency. In Dll4 mutant EBs, smooth muscle cells (SMCs) were seemingly unaffected and cardiomyocyte differentiation was increased, indicating that SMC specification is Dll4-independent while a normal dose of this Notch ligand is essential for the quantitative regulation of cardiomyogenesis.
  
  
  CONCLUSIONS
  This study highlights a previously unnoticed role for Dll4 in the quantitative regulation of early hemato-vascular precursors, further indicating that it is also involved on the timely emergence of mesoderm in early embryogenesis.
authors.affiliation: Unidade de Biologia da Hematopoiese, Instituto de Histologia e Biologia do Desenvolvimento, Faculdade de Medicina, Universidade de Lisboa, Lisbon, Portugal.
authors.forename: Ricardo
authors.initials: R
authors.lastname: Laranjeiro
authors.forename: Isabel
authors.initials: I
authors.lastname: Alcobia
authors.forename: Hélia
authors.initials: H
authors.lastname: Neves
authors.forename: Andreia C
authors.initials: AC
authors.lastname: Gomes
authors.forename: Pedro
authors.initials: P
authors.lastname: Saavedra
authors.forename: Catarina C
authors.initials: CC
authors.lastname: Carvalho
authors.forename: António
authors.initials: A
authors.lastname: Duarte
authors.forename: António
authors.initials: A
authors.lastname: Cidadão
authors.forename: Leonor
authors.initials: L
authors.lastname: Parreira
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D002135:Calcium-Binding Proteins; D002460:Cell Line; D004622:Embryo, Mammalian / Q000166:cytology / Q000378:metabolism*; D042783:Endothelial Cells / Q000166:cytology / Q000378:metabolism*; D004920:Erythropoiesis / Q000235:genetics / Q000502:physiology; D007150:Immunohistochemistry; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D032389:Myocytes, Smooth Muscle / Q000166:cytology / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002135:Calcium-Binding Proteins; C519665:DLL4 protein, mouse; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins