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Biological basis of angiogenesis and role of vascular endothelial growth factor-D
Published in A. R. Genazzani, Hormone Replacement Therapy and Cancer, 2020
Within the embryo, pluripotent embryonic precursors differentiate into hemangioblasts which form blood islands. Cells at the periphery of blood islands differentiate into endothelial cells, while the cells in the center differentiate into hemopoietic precursors. Recently, it has been pointed out that there could be a common precursor for endothelial and smooth muscle cell precursors4. Embryonic stem cells in vitro can be induced to differentiate toward hemopoietic cells, endothelial cells or mural cells. Non-adherent cells will generate hemopoietic cells while adherent cells can be forced to differentiate into endothelial cells or smooth muscle cells if treated with different growth factors (Figure 1). Interestingly, specific substrates induce different percentages of one or another cell type, suggesting that integrin expression plays an important role in the differentiation pathways. The common precursors express markers like CD31, CD34 and the receptor Flk1/vascular endothelial growth factor receptor-2. Vasculogenesis is not restricted to the embryo. Bone marrow-derived angioblasts circulating can, following an induction program not yet understood, initiate a vasculogenesis process5.
Tumor Angiogenesis
Published in Hans-Inge Peterson, Tumor Blood Circulation: Angiogenesis, Vascular Morphology and Blood Flow of Experimental and Human Tumors, 2020
In a consideration of the development of peripheral vessels, Arey6 considered that there were general principles of development which pertained to the following subjects: (1) the source of the angioblast, (2) the origin of embryonic vessels, (3) the formation of temporary capillary plexuses which were the forerunners of definitive vascular systems, (4) the emergence of larger pre-emptive channels within such provisional networks, (5) histogenetic advances in which additional tissue coats were laid down on certain channels, and (6) casual development. Arey considered that the primary tissue of blood vessels was endothelium, and that all else was auxilliary tissue. The first blood islands or earliest vascular primordia are clusters of cells arising on the yolk sac. These are at first compact masses between the splanchnic mesoderm and endoderm. Separation into peripheral cells (primitive endothelium) and more centrally located cells (primitive blood cells) soon occurs, and a plexus of vessels is formed. Progressive vascularization is observed. Although this tissue was originally considered to be the sole source of all blood vessels (the “angioblast theory"), later workers,7,8 took the position that mesenchyme throughout the embryo was able to differentiate into endothelium as needed, and eventually the concept of the local origin of blood vessel endothelium within the embryo was accepted.6 Once the initial circulation of the embryo is formed, the system is extended only by sprouting and subsequent transformation.
Hematopoietic System
Published in Pritam S. Sahota, James A. Popp, Jerry F. Hardisty, Chirukandath Gopinath, Page R. Bouchard, Toxicologic Pathology, 2018
Kristin Henson, Tanasa Osborne, Gregory S. Travlos
In the developing embryo, hematopoiesis initially occurs within the extraembryonic blood islands of the visceral yolk sac. Blood cells first appear in the blood islands at embryonic day (E) 7.0 to 7.5 in the mouse and human gestation day 16 and consist of a synchronously maturing wave of large erythroblasts (Golub and Cumano 2013; Lux et al. 2008; Oberlin et al. 2010; Palis et al. 1999). This initial wave of blood cell formation between E7.5 and E9.0 in the mouse is referred to as primitive hematopoiesis, including production of megakaryocytes from bipotential megakaryocyte-erythroid progenitor (MEP) cells as well as nonmonocyte-derived primitive macrophages (Frame et al. 2013; Shepard and Zon 2000; Tober et al. 2007). Primitive erythroid cells (EryP), large embryonic platelets, and primitive macrophages begin to circulate around E8.5 in the mouse and gestation day 21 in humans after the onset of cardiac contractions. EryP are large (400–700 fL) nucleated erythroid cells that mature and divide within the embryonic circulation. Maturation of EryP involves morphologic changes typical for adult erythroid maturation, including a decrease in cell size and volume, nuclear condensation, increasing amounts of hemoglobin, and ultimately, loss of nuclei (reviewed in Baron et al. 2012). Murine EryP contain low levels of adult α- and β-hemoglobins and embryonic hemoglobins (BH1-globin, ζ-globin, and εγ-globin), which have a high oxygen affinity to promote placental oxygen exchange (reviewed in Baron et al. 2012 and Palis et al. 2010). In addition to their role in tissue oxygenation, EryP may scavenge reactive oxygen species and are necessary to generate the shear forces within blood vessels needed for vascular remodeling (reviewed in Baron et al. 2013).
Incorporating placental tissue in cord blood banking for stem cell transplantation
Published in Expert Review of Hematology, 2018
Luciana Teofili, Antonietta R. Silini, Maria Bianchi, Caterina Giovanna Valentini, Ornella Parolini
The formation of the embryonic vascular system involves vasculogenesis and angiogenesis. Vasculogenesis, or blood vessel formation, occurs in the embryo and extraembryonic membranes during the third week when mesenchymal cells differentiate into vessel-forming, endothelial-cell precursors called angioblasts, which gather to form isolated cell clusters called blood islands, which are associated with the umbilical vesicle or endothelial cords within the embryo. The blood islands form small cavities and angioblasts flatten into endothelial cells that align along the cavities in the blood islands to form the endothelium. Vasculogenesis occurs when the endothelium-lined cavities fuse to form networks of endothelial channels. Angiogenesis takes place when vessels sprout into adjacent areas by endothelial budding and fuse with other vessels. The mesenchymal cells that surround the primitive blood vessels differentiate into the muscular and connective tissue elements of the vessels.
Hyalocyte origin, structure, and imaging
Published in Expert Review of Ophthalmology, 2022
Peter Wieghofer, Michael Engelbert, Toco YP Chui, Richard B Rosen, Taiji Sakamoto, J Sebag
Hematopoiesis can be subdivided into primitive hematopoiesis that is restricted to early embryonic development, and definitive hematopoiesis that takes place at later stages of development in the aorto-gonad-mesonephros (AGM) and the fetal liver (FL) as well as in the bone marrow established at the perinatal stages that remains active throughout life [52,53]. Primitive hematopoiesis is established in the hemogenic endothelium/hemangioblast of the extra-embryonic yolk sac that provides the blood island where precursors of both nucleated embryonic erythrocytes and primitive macrophages are created via the erythro-myeloid precursors (EMP) [54]. During development, EMPs further differentiate and their descendants colonize organs such as the brain or eye, before the intrinsic blood-brain or blood-retina barriers are formed, to become local tissue-resident macrophages including microglia [7,8,10,11,53,54]. Besides the developing organs that are reached via the embryonic circulation [3], they transiently colonize the fetal liver where progenitors of definitive hematopoiesis, derived from the AGM, can be found and establish the bone marrow later, prior to birth [53,55,56]. With regard to ciliary body macrophages, primitive hematopoiesis has been identified as the main source with only limited contribution from other hematopoietic organs including the fetal liver and the bone marrow [10]. With respect to hyalocytes, no embryonic fate mapping has been performed to date. However, human embryonic developmental stages have been investigated with respect to the local leukocyte populations by immunophenotyping [57]. The results suggest the presence of several markers that were attributed to hemangioblasts and suggested the existence of local blood islands remote from their well described localization in the yolk sac. Future experiments involving more contemporary methods including transcriptional profiling would help to decipher the former microscopic observations.