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Brock University
Daniel Glenday

Vasculogenesis, Angiogenesis, Hematopoesis Vasculogenesis – de novo formation of blood vessels during fetal life 3 stages: 1) embryonic splanchnic mesoderm mesenchyme  angioblasts angioblasts angioblasts fuse to form ENDOTHELIAL CORDS endothelial cords differentiation involves VEGF expression by endoderm VEGF (extra-embryonic splanchnic mesoderm also forms HSC’s) 2) angioblasts in cords  endothelium (also requires VEGF) lumen forms 3) cords coalesce in yolk sac and embryo  primary endothelial plexus primary endothelial plexus Angiogenesis – can continue throughout life to meet metabolic needs sprouting, branching, pruning supporting cells: smooth muscle and pericytes recruitment – mesenchyme secretes angiopoietin-1 angiopoietin endothelium binds APO via TIE receptors TIE receptors activated endothelium secretes PDGF  recruits cells activated endothelium secretes TGF-B  stops prolif. and induces supporting cell diff. occurs in embryo for mature vasculature (TIE2 for capillary sprouting) later for wound healing and tumor growth Vasculogenesis, Angiogenesis, Hematopoesis PRENATAL HEMATOPOESIS 3 Stages: involve site and globin switching 1. Mesoblastic (blood cells from yolk sac, chorion) ζ2 2 develop within blood islands of developing vessels blood islands 2. Hepatic (1/2 of all liver cells are RBC precursors) αγ fetal hemoglobin – higher oxygen affinity than adult liver/spleen secrete erythropoetin 3. Myeloid (accounts for most blood cell production at birth) αδ, αβ begins lymphocyte production POSTNATAL HEMATOPOESIS proceeds from a single hematopoetic pluripotent stem cell (HSC) HSC characteristics: - unlimited self-renewal - asymmetric division - unidirectional division myeloid lineage formed in bone marrow evidence for existence: lethally irradiated mice rescued by injection of bone marrow - hematopoetic cell colonies count on spleen was proportional to amt. of marrow injected - ***selecting for u
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