New morphological aspects of blood islands formation in the embryonic mouse hearts

Abstract

Vasculogenesis in embryonic hearts proceeds by formation of aggregates consisting of erythroblasts and endothelial cells. These aggregates are called blood-islands or blood-island-like structures. We aimed to characterize blood islands in mouse embryonic hearts at stages spanning from 11 dpc through 13 dpc, i.e. prior to the establishment of the coronary circulation. Our observations suggested that there are two types of blood islands. One formed by migrating nucleated erythroblasts, which associated with migrating endothelial cell and the second by in situ emergence of two kinds of cells belonging to separate populations: one resembling an erythroblast progenitor and the second resembling an endothelial-cell progenitor. The subepicardial blood islands contain nucleated erythroblasts, undifferentiated mesenchymal cells, platelets, and early lymphocytes. The subepicardial blood islands resemble vesicles with protruding prongs directed toward the myocardium. Ahead of the prongs, angiogenic sprouting and degradation of fibronectin is observed. Vesicles gradually change their shape from spherical to tubular at 13 dpc and grow and extend along the interventricular sulcuses forming vascular tubes. We presume that the vascular tubes located within the interventricular sulcuses are precursors of coronary veins. Our data seems to indicate that embryonic heart vasculogenesis is accompanied by hematopoiesis.

Insights into blood cell formation from hemogenic endothelium in lesser‐known anatomic sites

“…A third wave of hematopoiesis in the heart occurs between E11 and E14, and involves the formation of cardiac blood islands from the ventricular endocardium (Ratajska et al, ; Red‐Horse et al, ; Jankowska‐Steifer et al, ). Cardiac blood islands balloon out from the ventricular endocardium near the interventricular sulci and are associated with Runx1 + hematopoietic cells (Fig.…”

Extravascular endothelial and hematopoietic islands form through multiple pathways in midgestation mouse embryos

“…Between E11 and E14 ventricular endocardial cells near the interventricular sulci balloon outwards into the myocardium (Jankowska-Steifer et al, 2015, Red-Horse et al, 2010, Ratajska et al, 2009, Ratajska et al, 2006). These protrusions, called cardiac blood islands consist primarily of erythroblasts and megakaryocytes circumscribed by a single layer of endocardial cells (Jankowska-Steifer et al, 2015).…”

“…These protrusions, called cardiac blood islands consist primarily of erythroblasts and megakaryocytes circumscribed by a single layer of endocardial cells (Jankowska-Steifer et al, 2015). Cardiac blood islands are thought to pinch off from the ventricular endocardium and fuse with the coronary vessels, contributing to the development of the coronary vasculature (Ratajska et al, 2009, Red-Horse et al, 2010). We also noted the apparent merging of extravascular islands with the vasculature in the embryo proper.…”

Extending the knowledge in histochemistry and cell biology

“…Formation of so-called blood-islands containing erythroblasts and endothelial cells normally precedes vasculogenesis. Ratajska et al (2009) now characterized blood islands in mouse embryonic hearts from 11 dpc through 13 dpc, which is prior to the establishment of the coronary circulation. The authors found two types of blood islands: one formed by migrating nucleated erythroblasts and endothelial cells and the second one by emergence of erythroblast-like and endothelial-cell progenitors.…”