Embryogenesis of the First Circulating Endothelial Cells

Abstract

Prior to this study, the earliest appearance of circulating endothelial cells in warm-blooded animals was unknown. Time-lapse imaging of germ-line transformed Tie1-YFP reporter quail embryos combined with the endothelial marker antibody QH1 provides definitive evidence for the existence of circulating endothelial cells – from the very beginning of blood flow. Blood-smear counts of circulating cells from Tie1-YFP embryos showed that up to 30% of blood-borne cells are Tie1 positive; though cells expressing low levels of YFP were also positive for benzidine, a hemoglobin stain, suggesting that these cells were differentiating into erythroblasts. Electroporation-based time-lapse experiments, exclusively targeting the intra-embryonic mesoderm were combined with QH1 immunostaining. The latter antibody marks quail endothelial cells. Together the optical data provide conclusive evidence that endothelial cells can enter blood flow from vessels of the embryo proper, as well as from extra-embryonic areas. When Tie1-YFP positive cells and tissues are transplanted to wild type host embryos, fluorescent cells emigrate from such transplants and join host vessels; subsequently a few YFP cells are shed into circulation. These data establish that entering circulation is a commonplace activity of embryonic vascular endothelial cells. We conclude that in the class of vertebrates most closely related to mammals a normal component of primary vasculogenesis is production of endothelial cells that enter circulation from all vessels, both intra- and extra-embryonic.

Erythro-myeloid progenitors can differentiate from endothelial cells and modulate embryonic vascular remodeling

“…One of the daughter cells enters circulation, whereas the other remains in the vessel wall (t = 8.3 hr, yellow arrowhead). We previously observed endothelial cell division frequently preceding cell entry into circulation in avian embryos38. Our results here clearly demonstrate that the cells that differentiate into EMPs are luminal and take up AcLDL before EMP commitment occurs but stop taking up AcLDL once they enter circulation.…”

Development of the Heart Endocardium at an Early Stage of Chick Embryos Evaluated at Light‐ and Electron‐Microscopic Levels

“…These findings indicate that erythroid commitment occurs outside the heart. Furthermore, a quail‐chick parabiosis model has shown that circulating cells are able to differentiate into cardiac and vascular cell types (Zhang et al, ; Cui et al, ; Jaffredo and Yvernogeau, ). In our present results, any progenitor cells of erythroid lineage were not detected within the heart at both light‐ and electron‐microscopic levels.…”

The development of coronary vascular system

“…В дефінітивному форматі судинна система серця складається з артеріальної, венозної ланок, мікроциркуляторного сегмента, лімфатичної мережі. Вінцева судинна система формується з клітин-попередників, джерело яких знаходиться поза серцем, мігрують з утворенням епікарду, диферен-цюються в ендотеліальні клітини, гладко -м'язові клітини та фібробласти, з утворенням первинної судинної мережі [2]. На початковому етапі кардіогенезу, коли камери серця мають трабекулярну будову, кардіоміоцити отримують кисень шляхом дифузії з порожнин серця.…”