Abstract
Vasculogenesis and hematopoiesis are co-localized in the embryonic body, but precise phenotypes of the cells contributing to these processes are not defined. The aim of this study was to characterize phenotypic profiles and location of putative vasculogenic and hematopoietic cellular progenitors in the embryonic mouse heart. Confocal microscopy, as well as ultrastructural and stereomicroscopic analyses, was performed on immunohistochemical whole-mount-stained or sectioned hearts at stages 11.5–14 dpc. A FASC analysis was conducted to quantify putative vasculogenic and hematopoietic cells. We found subepicardial blood islands in the form of foci of accumulation of cells belonging to erythroblastic and megakaryocytic lineages at various stages of maturation, exhibiting phenotypes: GATA2+/CD41+, GATA2−/CD41+, GATA2+/CD71−, GATA2−/CD71+, Fli1+/CD71+, Fli1−/CD71+, with a majority of cells expressing the Ter119 antigen, but none of them expressing Flk1. The subepicardium and the outflow tract endothelium were recognized to be the areas where progenitor cells were scattered or adjoining the endothelial cells. These progenitor cells were characterized as possessing the following antigens: CD45+/Fli1+, CD41+/Flk1+, Flk1+/Fli1+. A FACS analysis demonstrated that the CD41/Flk1 double-positive population of cells constituted 2.68 % of total cell population isolated from 12.5 dpc hearts. Vessels and tubules were positive for CD31, Flk1, Fli1, Tie2, including blood islands endothelia. The endocardial wall endothelia were found to function as an anchoring apparatus for megakaryocytes releasing platelets into the cardiac cavities. Phenotypic characteristics of vasculogenic (Flk1+/Fli1+) and hematopoietic (GATA2+/CD71+, CD41+/GATA2+) progenitors, as well as the putative hemogenic endothelium (Flk1+/CD41+) in embryonic mouse hearts, have been presented. Cardiac blood islands, the subepicardium and endothelium of the outflow tract cushions have been defined as areas where these progenitor cells can be found.
Highlights
The cardiovascular system is the first one which develops and functions during the embryonic development
It has been reported that hematopoiesis takes place during the prenatal formation of blood vessels and that vascular endothelial cells and hematopoietic cells are in a close relationship during ontogeny
Due to close spatial and temporal relationships between the vasculogenesis and hematopoiesis and overlapping phenotypes of the endothelium involved in neovascularization and hematopoiesis, we propose to define the foci of these events by the use of multiple markers describing hematopoietic and vasculogenic activity in the developing heart in situ
Summary
The cardiovascular system is the first one which develops and functions during the embryonic development. The cardiovascular system develops via vasculogenesis, i.e., de novo formation of blood vessels from a precursor cell—angioblast, and via angiogenesis, i.e., sprouting from the preexisting vessels. Precursor cells are endothelial cells of an existing vessel. It has been reported that hematopoiesis takes place during the prenatal formation of blood vessels and that vascular endothelial cells and hematopoietic cells are in a close relationship during ontogeny. The first postulates the existence of a common precursor of hematopoietic and endothelial lineages, the hemangioblast. The second one assumes the presence of hemogenic endothelium, which arises by dedifferentiation of mature endothelium into hematopoietic lineage. These two models describing the embryonic origin of hematopoietic cells have been regarded as mutually exclusive for many years. Recent studies suggest that they may be combined and complement each other and that hemangioblasts may be linked to the hematopoietic cell progeny via a hemogenic endothelium (Lancrin et al 2009; Antas et al 2013)
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